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exec.c

/*
 *  linux/fs/exec.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * #!-checking implemented by tytso.
 */
/*
 * Demand-loading implemented 01.12.91 - no need to read anything but
 * the header into memory. The inode of the executable is put into
 * "current->executable", and page faults do the actual loading. Clean.
 *
 * Once more I can proudly say that linux stood up to being changed: it
 * was less than 2 hours work to get demand-loading completely implemented.
 *
 * Demand loading changed July 1993 by Eric Youngdale.   Use mmap instead,
 * current->executable is only used by the procfs.  This allows a dispatch
 * table to check for several different types  of binary formats.  We keep
 * trying until we recognize the file or we run out of supported binary
 * formats. 
 */

#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/swap.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/perf_event.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/proc_fs.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/tracehook.h>
#include <linux/kmod.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>

#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/tlb.h>
#include "internal.h"

int core_uses_pid;
char core_pattern[CORENAME_MAX_SIZE] = "core";
unsigned int core_pipe_limit;
int suid_dumpable = 0;

00069 struct core_name {
      char *corename;
      int used, size;
};
static atomic_t call_count = ATOMIC_INIT(1);

/* The maximal length of core_pattern is also specified in sysctl.c */

static LIST_HEAD(formats);
static DEFINE_RWLOCK(binfmt_lock);

int __register_binfmt(struct linux_binfmt * fmt, int insert)
{
      if (!fmt)
            return -EINVAL;
      write_lock(&binfmt_lock);
      insert ? list_add(&fmt->lh, &formats) :
             list_add_tail(&fmt->lh, &formats);
      write_unlock(&binfmt_lock);
      return 0;   
}

EXPORT_SYMBOL(__register_binfmt);

void unregister_binfmt(struct linux_binfmt * fmt)
{
      write_lock(&binfmt_lock);
      list_del(&fmt->lh);
      write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(unregister_binfmt);

static inline void put_binfmt(struct linux_binfmt * fmt)
{
      module_put(fmt->module);
}

/*
 * Note that a shared library must be both readable and executable due to
 * security reasons.
 *
 * Also note that we take the address to load from from the file itself.
 */
SYSCALL_DEFINE1(uselib, const char __user *, library)
{
      struct file *file;
      char *tmp = getname(library);
      int error = PTR_ERR(tmp);

      if (IS_ERR(tmp))
            goto out;

      file = do_filp_open(AT_FDCWD, tmp,
                        O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
                        MAY_READ | MAY_EXEC | MAY_OPEN);
      putname(tmp);
      error = PTR_ERR(file);
      if (IS_ERR(file))
            goto out;

      error = -EINVAL;
      if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
            goto exit;

      error = -EACCES;
      if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
            goto exit;

      fsnotify_open(file);

      error = -ENOEXEC;
      if(file->f_op) {
            struct linux_binfmt * fmt;

            read_lock(&binfmt_lock);
            list_for_each_entry(fmt, &formats, lh) {
                  if (!fmt->load_shlib)
                        continue;
                  if (!try_module_get(fmt->module))
                        continue;
                  read_unlock(&binfmt_lock);
                  error = fmt->load_shlib(file);
                  read_lock(&binfmt_lock);
                  put_binfmt(fmt);
                  if (error != -ENOEXEC)
                        break;
            }
            read_unlock(&binfmt_lock);
      }
exit:
      fput(file);
out:
      return error;
}

#ifdef CONFIG_MMU

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
            int write)
{
      struct page *page;
      int ret;

#ifdef CONFIG_STACK_GROWSUP
      if (write) {
            ret = expand_stack_downwards(bprm->vma, pos);
            if (ret < 0)
                  return NULL;
      }
#endif
      ret = get_user_pages(current, bprm->mm, pos,
                  1, write, 1, &page, NULL);
      if (ret <= 0)
            return NULL;

      if (write) {
            unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
            struct rlimit *rlim;

            /*
             * We've historically supported up to 32 pages (ARG_MAX)
             * of argument strings even with small stacks
             */
            if (size <= ARG_MAX)
                  return page;

            /*
             * Limit to 1/4-th the stack size for the argv+env strings.
             * This ensures that:
             *  - the remaining binfmt code will not run out of stack space,
             *  - the program will have a reasonable amount of stack left
             *    to work from.
             */
            rlim = current->signal->rlim;
            if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) {
                  put_page(page);
                  return NULL;
            }
      }

      return page;
}

static void put_arg_page(struct page *page)
{
      put_page(page);
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
}

static void free_arg_pages(struct linux_binprm *bprm)
{
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
            struct page *page)
{
      flush_cache_page(bprm->vma, pos, page_to_pfn(page));
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
      int err;
      struct vm_area_struct *vma = NULL;
      struct mm_struct *mm = bprm->mm;

      bprm->vma = vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
      if (!vma)
            return -ENOMEM;

      down_write(&mm->mmap_sem);
      vma->vm_mm = mm;

      /*
       * Place the stack at the largest stack address the architecture
       * supports. Later, we'll move this to an appropriate place. We don't
       * use STACK_TOP because that can depend on attributes which aren't
       * configured yet.
       */
      BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
      vma->vm_end = STACK_TOP_MAX;
      vma->vm_start = vma->vm_end - PAGE_SIZE;
      vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
      vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
      INIT_LIST_HEAD(&vma->anon_vma_chain);
      err = insert_vm_struct(mm, vma);
      if (err)
            goto err;

      mm->stack_vm = mm->total_vm = 1;
      up_write(&mm->mmap_sem);
      bprm->p = vma->vm_end - sizeof(void *);
      return 0;
err:
      up_write(&mm->mmap_sem);
      bprm->vma = NULL;
      kmem_cache_free(vm_area_cachep, vma);
      return err;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
      return len <= MAX_ARG_STRLEN;
}

#else

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
            int write)
{
      struct page *page;

      page = bprm->page[pos / PAGE_SIZE];
      if (!page && write) {
            page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
            if (!page)
                  return NULL;
            bprm->page[pos / PAGE_SIZE] = page;
      }

      return page;
}

static void put_arg_page(struct page *page)
{
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
      if (bprm->page[i]) {
            __free_page(bprm->page[i]);
            bprm->page[i] = NULL;
      }
}

static void free_arg_pages(struct linux_binprm *bprm)
{
      int i;

      for (i = 0; i < MAX_ARG_PAGES; i++)
            free_arg_page(bprm, i);
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
            struct page *page)
{
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
      bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
      return 0;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
      return len <= bprm->p;
}

#endif /* CONFIG_MMU */

/*
 * Create a new mm_struct and populate it with a temporary stack
 * vm_area_struct.  We don't have enough context at this point to set the stack
 * flags, permissions, and offset, so we use temporary values.  We'll update
 * them later in setup_arg_pages().
 */
int bprm_mm_init(struct linux_binprm *bprm)
{
      int err;
      struct mm_struct *mm = NULL;

      bprm->mm = mm = mm_alloc();
      err = -ENOMEM;
      if (!mm)
            goto err;

      err = init_new_context(current, mm);
      if (err)
            goto err;

      err = __bprm_mm_init(bprm);
      if (err)
            goto err;

      return 0;

err:
      if (mm) {
            bprm->mm = NULL;
            mmdrop(mm);
      }

      return err;
}

/*
 * count() counts the number of strings in array ARGV.
 */
static int count(const char __user * const __user * argv, int max)
{
      int i = 0;

      if (argv != NULL) {
            for (;;) {
                  const char __user * p;

                  if (get_user(p, argv))
                        return -EFAULT;
                  if (!p)
                        break;
                  argv++;
                  if (i++ >= max)
                        return -E2BIG;

                  if (fatal_signal_pending(current))
                        return -ERESTARTNOHAND;
                  cond_resched();
            }
      }
      return i;
}

/*
 * 'copy_strings()' copies argument/environment strings from the old
 * processes's memory to the new process's stack.  The call to get_user_pages()
 * ensures the destination page is created and not swapped out.
 */
static int copy_strings(int argc, const char __user *const __user *argv,
                  struct linux_binprm *bprm)
{
      struct page *kmapped_page = NULL;
      char *kaddr = NULL;
      unsigned long kpos = 0;
      int ret;

      while (argc-- > 0) {
            const char __user *str;
            int len;
            unsigned long pos;

            if (get_user(str, argv+argc) ||
                        !(len = strnlen_user(str, MAX_ARG_STRLEN))) {
                  ret = -EFAULT;
                  goto out;
            }

            if (!valid_arg_len(bprm, len)) {
                  ret = -E2BIG;
                  goto out;
            }

            /* We're going to work our way backwords. */
            pos = bprm->p;
            str += len;
            bprm->p -= len;

            while (len > 0) {
                  int offset, bytes_to_copy;

                  if (fatal_signal_pending(current)) {
                        ret = -ERESTARTNOHAND;
                        goto out;
                  }
                  cond_resched();

                  offset = pos % PAGE_SIZE;
                  if (offset == 0)
                        offset = PAGE_SIZE;

                  bytes_to_copy = offset;
                  if (bytes_to_copy > len)
                        bytes_to_copy = len;

                  offset -= bytes_to_copy;
                  pos -= bytes_to_copy;
                  str -= bytes_to_copy;
                  len -= bytes_to_copy;

                  if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                        struct page *page;

                        page = get_arg_page(bprm, pos, 1);
                        if (!page) {
                              ret = -E2BIG;
                              goto out;
                        }

                        if (kmapped_page) {
                              flush_kernel_dcache_page(kmapped_page);
                              kunmap(kmapped_page);
                              put_arg_page(kmapped_page);
                        }
                        kmapped_page = page;
                        kaddr = kmap(kmapped_page);
                        kpos = pos & PAGE_MASK;
                        flush_arg_page(bprm, kpos, kmapped_page);
                  }
                  if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
                        ret = -EFAULT;
                        goto out;
                  }
            }
      }
      ret = 0;
out:
      if (kmapped_page) {
            flush_kernel_dcache_page(kmapped_page);
            kunmap(kmapped_page);
            put_arg_page(kmapped_page);
      }
      return ret;
}

/*
 * Like copy_strings, but get argv and its values from kernel memory.
 */
int copy_strings_kernel(int argc, const char *const *argv,
                  struct linux_binprm *bprm)
{
      int r;
      mm_segment_t oldfs = get_fs();
      set_fs(KERNEL_DS);
      r = copy_strings(argc, (const char __user *const  __user *)argv, bprm);
      set_fs(oldfs);
      return r;
}
EXPORT_SYMBOL(copy_strings_kernel);

#ifdef CONFIG_MMU

/*
 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
 * the binfmt code determines where the new stack should reside, we shift it to
 * its final location.  The process proceeds as follows:
 *
 * 1) Use shift to calculate the new vma endpoints.
 * 2) Extend vma to cover both the old and new ranges.  This ensures the
 *    arguments passed to subsequent functions are consistent.
 * 3) Move vma's page tables to the new range.
 * 4) Free up any cleared pgd range.
 * 5) Shrink the vma to cover only the new range.
 */
static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
{
      struct mm_struct *mm = vma->vm_mm;
      unsigned long old_start = vma->vm_start;
      unsigned long old_end = vma->vm_end;
      unsigned long length = old_end - old_start;
      unsigned long new_start = old_start - shift;
      unsigned long new_end = old_end - shift;
      struct mmu_gather *tlb;

      BUG_ON(new_start > new_end);

      /*
       * ensure there are no vmas between where we want to go
       * and where we are
       */
      if (vma != find_vma(mm, new_start))
            return -EFAULT;

      /*
       * cover the whole range: [new_start, old_end)
       */
      if (vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL))
            return -ENOMEM;

      /*
       * move the page tables downwards, on failure we rely on
       * process cleanup to remove whatever mess we made.
       */
      if (length != move_page_tables(vma, old_start,
                               vma, new_start, length))
            return -ENOMEM;

      lru_add_drain();
      tlb = tlb_gather_mmu(mm, 0);
      if (new_end > old_start) {
            /*
             * when the old and new regions overlap clear from new_end.
             */
            free_pgd_range(tlb, new_end, old_end, new_end,
                  vma->vm_next ? vma->vm_next->vm_start : 0);
      } else {
            /*
             * otherwise, clean from old_start; this is done to not touch
             * the address space in [new_end, old_start) some architectures
             * have constraints on va-space that make this illegal (IA64) -
             * for the others its just a little faster.
             */
            free_pgd_range(tlb, old_start, old_end, new_end,
                  vma->vm_next ? vma->vm_next->vm_start : 0);
      }
      tlb_finish_mmu(tlb, new_end, old_end);

      /*
       * Shrink the vma to just the new range.  Always succeeds.
       */
      vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);

      return 0;
}

/*
 * Finalizes the stack vm_area_struct. The flags and permissions are updated,
 * the stack is optionally relocated, and some extra space is added.
 */
int setup_arg_pages(struct linux_binprm *bprm,
                unsigned long stack_top,
                int executable_stack)
{
      unsigned long ret;
      unsigned long stack_shift;
      struct mm_struct *mm = current->mm;
      struct vm_area_struct *vma = bprm->vma;
      struct vm_area_struct *prev = NULL;
      unsigned long vm_flags;
      unsigned long stack_base;
      unsigned long stack_size;
      unsigned long stack_expand;
      unsigned long rlim_stack;

#ifdef CONFIG_STACK_GROWSUP
      /* Limit stack size to 1GB */
      stack_base = rlimit_max(RLIMIT_STACK);
      if (stack_base > (1 << 30))
            stack_base = 1 << 30;

      /* Make sure we didn't let the argument array grow too large. */
      if (vma->vm_end - vma->vm_start > stack_base)
            return -ENOMEM;

      stack_base = PAGE_ALIGN(stack_top - stack_base);

      stack_shift = vma->vm_start - stack_base;
      mm->arg_start = bprm->p - stack_shift;
      bprm->p = vma->vm_end - stack_shift;
#else
      stack_top = arch_align_stack(stack_top);
      stack_top = PAGE_ALIGN(stack_top);

      if (unlikely(stack_top < mmap_min_addr) ||
          unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr))
            return -ENOMEM;

      stack_shift = vma->vm_end - stack_top;

      bprm->p -= stack_shift;
      mm->arg_start = bprm->p;
#endif

      if (bprm->loader)
            bprm->loader -= stack_shift;
      bprm->exec -= stack_shift;

      down_write(&mm->mmap_sem);
      vm_flags = VM_STACK_FLAGS;

      /*
       * Adjust stack execute permissions; explicitly enable for
       * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
       * (arch default) otherwise.
       */
      if (unlikely(executable_stack == EXSTACK_ENABLE_X))
            vm_flags |= VM_EXEC;
      else if (executable_stack == EXSTACK_DISABLE_X)
            vm_flags &= ~VM_EXEC;
      vm_flags |= mm->def_flags;
      vm_flags |= VM_STACK_INCOMPLETE_SETUP;

      ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
                  vm_flags);
      if (ret)
            goto out_unlock;
      BUG_ON(prev != vma);

      /* Move stack pages down in memory. */
      if (stack_shift) {
            ret = shift_arg_pages(vma, stack_shift);
            if (ret)
                  goto out_unlock;
      }

      /* mprotect_fixup is overkill to remove the temporary stack flags */
      vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;

      stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
      stack_size = vma->vm_end - vma->vm_start;
      /*
       * Align this down to a page boundary as expand_stack
       * will align it up.
       */
      rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
#ifdef CONFIG_STACK_GROWSUP
      if (stack_size + stack_expand > rlim_stack)
            stack_base = vma->vm_start + rlim_stack;
      else
            stack_base = vma->vm_end + stack_expand;
#else
      if (stack_size + stack_expand > rlim_stack)
            stack_base = vma->vm_end - rlim_stack;
      else
            stack_base = vma->vm_start - stack_expand;
#endif
      current->mm->start_stack = bprm->p;
      ret = expand_stack(vma, stack_base);
      if (ret)
            ret = -EFAULT;

out_unlock:
      up_write(&mm->mmap_sem);
      return ret;
}
EXPORT_SYMBOL(setup_arg_pages);

#endif /* CONFIG_MMU */

struct file *open_exec(const char *name)
{
      struct file *file;
      int err;

      file = do_filp_open(AT_FDCWD, name,
                        O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
                        MAY_EXEC | MAY_OPEN);
      if (IS_ERR(file))
            goto out;

      err = -EACCES;
      if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
            goto exit;

      if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
            goto exit;

      fsnotify_open(file);

      err = deny_write_access(file);
      if (err)
            goto exit;

out:
      return file;

exit:
      fput(file);
      return ERR_PTR(err);
}
EXPORT_SYMBOL(open_exec);

int kernel_read(struct file *file, loff_t offset,
            char *addr, unsigned long count)
{
      mm_segment_t old_fs;
      loff_t pos = offset;
      int result;

      old_fs = get_fs();
      set_fs(get_ds());
      /* The cast to a user pointer is valid due to the set_fs() */
      result = vfs_read(file, (void __user *)addr, count, &pos);
      set_fs(old_fs);
      return result;
}

EXPORT_SYMBOL(kernel_read);

static int exec_mmap(struct mm_struct *mm)
{
      struct task_struct *tsk;
      struct mm_struct * old_mm, *active_mm;

      /* Notify parent that we're no longer interested in the old VM */
      tsk = current;
      old_mm = current->mm;
      sync_mm_rss(tsk, old_mm);
      mm_release(tsk, old_mm);

      if (old_mm) {
            /*
             * Make sure that if there is a core dump in progress
             * for the old mm, we get out and die instead of going
             * through with the exec.  We must hold mmap_sem around
             * checking core_state and changing tsk->mm.
             */
            down_read(&old_mm->mmap_sem);
            if (unlikely(old_mm->core_state)) {
                  up_read(&old_mm->mmap_sem);
                  return -EINTR;
            }
      }
      task_lock(tsk);
      active_mm = tsk->active_mm;
      tsk->mm = mm;
      tsk->active_mm = mm;
      activate_mm(active_mm, mm);
      if (old_mm && tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
            atomic_dec(&old_mm->oom_disable_count);
            atomic_inc(&tsk->mm->oom_disable_count);
      }
      task_unlock(tsk);
      arch_pick_mmap_layout(mm);
      if (old_mm) {
            up_read(&old_mm->mmap_sem);
            BUG_ON(active_mm != old_mm);
            mm_update_next_owner(old_mm);
            mmput(old_mm);
            return 0;
      }
      mmdrop(active_mm);
      return 0;
}

/*
 * This function makes sure the current process has its own signal table,
 * so that flush_signal_handlers can later reset the handlers without
 * disturbing other processes.  (Other processes might share the signal
 * table via the CLONE_SIGHAND option to clone().)
 */
static int de_thread(struct task_struct *tsk)
{
      struct signal_struct *sig = tsk->signal;
      struct sighand_struct *oldsighand = tsk->sighand;
      spinlock_t *lock = &oldsighand->siglock;

      if (thread_group_empty(tsk))
            goto no_thread_group;

      /*
       * Kill all other threads in the thread group.
       */
      spin_lock_irq(lock);
      if (signal_group_exit(sig)) {
            /*
             * Another group action in progress, just
             * return so that the signal is processed.
             */
            spin_unlock_irq(lock);
            return -EAGAIN;
      }

      sig->group_exit_task = tsk;
      sig->notify_count = zap_other_threads(tsk);
      if (!thread_group_leader(tsk))
            sig->notify_count--;

      while (sig->notify_count) {
            __set_current_state(TASK_UNINTERRUPTIBLE);
            spin_unlock_irq(lock);
            schedule();
            spin_lock_irq(lock);
      }
      spin_unlock_irq(lock);

      /*
       * At this point all other threads have exited, all we have to
       * do is to wait for the thread group leader to become inactive,
       * and to assume its PID:
       */
      if (!thread_group_leader(tsk)) {
            struct task_struct *leader = tsk->group_leader;

            sig->notify_count = -1; /* for exit_notify() */
            for (;;) {
                  write_lock_irq(&tasklist_lock);
                  if (likely(leader->exit_state))
                        break;
                  __set_current_state(TASK_UNINTERRUPTIBLE);
                  write_unlock_irq(&tasklist_lock);
                  schedule();
            }

            /*
             * The only record we have of the real-time age of a
             * process, regardless of execs it's done, is start_time.
             * All the past CPU time is accumulated in signal_struct
             * from sister threads now dead.  But in this non-leader
             * exec, nothing survives from the original leader thread,
             * whose birth marks the true age of this process now.
             * When we take on its identity by switching to its PID, we
             * also take its birthdate (always earlier than our own).
             */
            tsk->start_time = leader->start_time;

            BUG_ON(!same_thread_group(leader, tsk));
            BUG_ON(has_group_leader_pid(tsk));
            /*
             * An exec() starts a new thread group with the
             * TGID of the previous thread group. Rehash the
             * two threads with a switched PID, and release
             * the former thread group leader:
             */

            /* Become a process group leader with the old leader's pid.
             * The old leader becomes a thread of the this thread group.
             * Note: The old leader also uses this pid until release_task
             *       is called.  Odd but simple and correct.
             */
            detach_pid(tsk, PIDTYPE_PID);
            tsk->pid = leader->pid;
            attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
            transfer_pid(leader, tsk, PIDTYPE_PGID);
            transfer_pid(leader, tsk, PIDTYPE_SID);

            list_replace_rcu(&leader->tasks, &tsk->tasks);
            list_replace_init(&leader->sibling, &tsk->sibling);

            tsk->group_leader = tsk;
            leader->group_leader = tsk;

            tsk->exit_signal = SIGCHLD;

            BUG_ON(leader->exit_state != EXIT_ZOMBIE);
            leader->exit_state = EXIT_DEAD;
            write_unlock_irq(&tasklist_lock);

            release_task(leader);
      }

      sig->group_exit_task = NULL;
      sig->notify_count = 0;

no_thread_group:
      if (current->mm)
            setmax_mm_hiwater_rss(&sig->maxrss, current->mm);

      exit_itimers(sig);
      flush_itimer_signals();

      if (atomic_read(&oldsighand->count) != 1) {
            struct sighand_struct *newsighand;
            /*
             * This ->sighand is shared with the CLONE_SIGHAND
             * but not CLONE_THREAD task, switch to the new one.
             */
            newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
            if (!newsighand)
                  return -ENOMEM;

            atomic_set(&newsighand->count, 1);
            memcpy(newsighand->action, oldsighand->action,
                   sizeof(newsighand->action));

            write_lock_irq(&tasklist_lock);
            spin_lock(&oldsighand->siglock);
            rcu_assign_pointer(tsk->sighand, newsighand);
            spin_unlock(&oldsighand->siglock);
            write_unlock_irq(&tasklist_lock);

            __cleanup_sighand(oldsighand);
      }

      BUG_ON(!thread_group_leader(tsk));
      return 0;
}

/*
 * These functions flushes out all traces of the currently running executable
 * so that a new one can be started
 */
static void flush_old_files(struct files_struct * files)
{
      long j = -1;
      struct fdtable *fdt;

      spin_lock(&files->file_lock);
      for (;;) {
            unsigned long set, i;

            j++;
            i = j * __NFDBITS;
            fdt = files_fdtable(files);
            if (i >= fdt->max_fds)
                  break;
            set = fdt->close_on_exec->fds_bits[j];
            if (!set)
                  continue;
            fdt->close_on_exec->fds_bits[j] = 0;
            spin_unlock(&files->file_lock);
            for ( ; set ; i++,set >>= 1) {
                  if (set & 1) {
                        sys_close(i);
                  }
            }
            spin_lock(&files->file_lock);

      }
      spin_unlock(&files->file_lock);
}

char *get_task_comm(char *buf, struct task_struct *tsk)
{
      /* buf must be at least sizeof(tsk->comm) in size */
      task_lock(tsk);
      strncpy(buf, tsk->comm, sizeof(tsk->comm));
      task_unlock(tsk);
      return buf;
}

void set_task_comm(struct task_struct *tsk, char *buf)
{
      task_lock(tsk);

      /*
       * Threads may access current->comm without holding
       * the task lock, so write the string carefully.
       * Readers without a lock may see incomplete new
       * names but are safe from non-terminating string reads.
       */
      memset(tsk->comm, 0, TASK_COMM_LEN);
      wmb();
      strlcpy(tsk->comm, buf, sizeof(tsk->comm));
      task_unlock(tsk);
      perf_event_comm(tsk);
}

int flush_old_exec(struct linux_binprm * bprm)
{
      int retval;

      /*
       * Make sure we have a private signal table and that
       * we are unassociated from the previous thread group.
       */
      retval = de_thread(current);
      if (retval)
            goto out;

      set_mm_exe_file(bprm->mm, bprm->file);

      /*
       * Release all of the old mmap stuff
       */
      retval = exec_mmap(bprm->mm);
      if (retval)
            goto out;

      bprm->mm = NULL;        /* We're using it now */

      current->flags &= ~(PF_RANDOMIZE | PF_KTHREAD);
      flush_thread();
      current->personality &= ~bprm->per_clear;

      return 0;

out:
      return retval;
}
EXPORT_SYMBOL(flush_old_exec);

void setup_new_exec(struct linux_binprm * bprm)
{
      int i, ch;
      const char *name;
      char tcomm[sizeof(current->comm)];

      arch_pick_mmap_layout(current->mm);

      /* This is the point of no return */
      current->sas_ss_sp = current->sas_ss_size = 0;

      if (current_euid() == current_uid() && current_egid() == current_gid())
            set_dumpable(current->mm, 1);
      else
            set_dumpable(current->mm, suid_dumpable);

      name = bprm->filename;

      /* Copies the binary name from after last slash */
      for (i=0; (ch = *(name++)) != '\0';) {
            if (ch == '/')
                  i = 0; /* overwrite what we wrote */
            else
                  if (i < (sizeof(tcomm) - 1))
                        tcomm[i++] = ch;
      }
      tcomm[i] = '\0';
      set_task_comm(current, tcomm);

      /* Set the new mm task size. We have to do that late because it may
       * depend on TIF_32BIT which is only updated in flush_thread() on
       * some architectures like powerpc
       */
      current->mm->task_size = TASK_SIZE;

      /* install the new credentials */
      if (bprm->cred->uid != current_euid() ||
          bprm->cred->gid != current_egid()) {
            current->pdeath_signal = 0;
      } else if (file_permission(bprm->file, MAY_READ) ||
               bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) {
            set_dumpable(current->mm, suid_dumpable);
      }

      /*
       * Flush performance counters when crossing a
       * security domain:
       */
      if (!get_dumpable(current->mm))
            perf_event_exit_task(current);

      /* An exec changes our domain. We are no longer part of the thread
         group */

      current->self_exec_id++;
                  
      flush_signal_handlers(current, 0);
      flush_old_files(current->files);
}
EXPORT_SYMBOL(setup_new_exec);

/*
 * Prepare credentials and lock ->cred_guard_mutex.
 * install_exec_creds() commits the new creds and drops the lock.
 * Or, if exec fails before, free_bprm() should release ->cred and
 * and unlock.
 */
int prepare_bprm_creds(struct linux_binprm *bprm)
{
      if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
            return -ERESTARTNOINTR;

      bprm->cred = prepare_exec_creds();
      if (likely(bprm->cred))
            return 0;

      mutex_unlock(&current->signal->cred_guard_mutex);
      return -ENOMEM;
}

void free_bprm(struct linux_binprm *bprm)
{
      free_arg_pages(bprm);
      if (bprm->cred) {
            mutex_unlock(&current->signal->cred_guard_mutex);
            abort_creds(bprm->cred);
      }
      kfree(bprm);
}

/*
 * install the new credentials for this executable
 */
void install_exec_creds(struct linux_binprm *bprm)
{
      security_bprm_committing_creds(bprm);

      commit_creds(bprm->cred);
      bprm->cred = NULL;
      /*
       * cred_guard_mutex must be held at least to this point to prevent
       * ptrace_attach() from altering our determination of the task's
       * credentials; any time after this it may be unlocked.
       */
      security_bprm_committed_creds(bprm);
      mutex_unlock(&current->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);

/*
 * determine how safe it is to execute the proposed program
 * - the caller must hold ->cred_guard_mutex to protect against
 *   PTRACE_ATTACH
 */
int check_unsafe_exec(struct linux_binprm *bprm)
{
      struct task_struct *p = current, *t;
      unsigned n_fs;
      int res = 0;

      bprm->unsafe = tracehook_unsafe_exec(p);

      n_fs = 1;
      spin_lock(&p->fs->lock);
      rcu_read_lock();
      for (t = next_thread(p); t != p; t = next_thread(t)) {
            if (t->fs == p->fs)
                  n_fs++;
      }
      rcu_read_unlock();

      if (p->fs->users > n_fs) {
            bprm->unsafe |= LSM_UNSAFE_SHARE;
      } else {
            res = -EAGAIN;
            if (!p->fs->in_exec) {
                  p->fs->in_exec = 1;
                  res = 1;
            }
      }
      spin_unlock(&p->fs->lock);

      return res;
}

/* 
 * Fill the binprm structure from the inode. 
 * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
 *
 * This may be called multiple times for binary chains (scripts for example).
 */
int prepare_binprm(struct linux_binprm *bprm)
{
      umode_t mode;
      struct inode * inode = bprm->file->f_path.dentry->d_inode;
      int retval;

      mode = inode->i_mode;
      if (bprm->file->f_op == NULL)
            return -EACCES;

      /* clear any previous set[ug]id data from a previous binary */
      bprm->cred->euid = current_euid();
      bprm->cred->egid = current_egid();

      if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) {
            /* Set-uid? */
            if (mode & S_ISUID) {
                  bprm->per_clear |= PER_CLEAR_ON_SETID;
                  bprm->cred->euid = inode->i_uid;
            }

            /* Set-gid? */
            /*
             * If setgid is set but no group execute bit then this
             * is a candidate for mandatory locking, not a setgid
             * executable.
             */
            if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
                  bprm->per_clear |= PER_CLEAR_ON_SETID;
                  bprm->cred->egid = inode->i_gid;
            }
      }

      /* fill in binprm security blob */
      retval = security_bprm_set_creds(bprm);
      if (retval)
            return retval;
      bprm->cred_prepared = 1;

      memset(bprm->buf, 0, BINPRM_BUF_SIZE);
      return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
}

EXPORT_SYMBOL(prepare_binprm);

/*
 * Arguments are '\0' separated strings found at the location bprm->p
 * points to; chop off the first by relocating brpm->p to right after
 * the first '\0' encountered.
 */
int remove_arg_zero(struct linux_binprm *bprm)
{
      int ret = 0;
      unsigned long offset;
      char *kaddr;
      struct page *page;

      if (!bprm->argc)
            return 0;

      do {
            offset = bprm->p & ~PAGE_MASK;
            page = get_arg_page(bprm, bprm->p, 0);
            if (!page) {
                  ret = -EFAULT;
                  goto out;
            }
            kaddr = kmap_atomic(page, KM_USER0);

            for (; offset < PAGE_SIZE && kaddr[offset];
                        offset++, bprm->p++)
                  ;

            kunmap_atomic(kaddr, KM_USER0);
            put_arg_page(page);

            if (offset == PAGE_SIZE)
                  free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
      } while (offset == PAGE_SIZE);

      bprm->p++;
      bprm->argc--;
      ret = 0;

out:
      return ret;
}
EXPORT_SYMBOL(remove_arg_zero);

/*
 * cycle the list of binary formats handler, until one recognizes the image
 */
int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
{
      unsigned int depth = bprm->recursion_depth;
      int try,retval;
      struct linux_binfmt *fmt;

      retval = security_bprm_check(bprm);
      if (retval)
            return retval;

      /* kernel module loader fixup */
      /* so we don't try to load run modprobe in kernel space. */
      set_fs(USER_DS);

      retval = audit_bprm(bprm);
      if (retval)
            return retval;

      retval = -ENOENT;
      for (try=0; try<2; try++) {
            read_lock(&binfmt_lock);
            list_for_each_entry(fmt, &formats, lh) {
                  int (*fn)(struct linux_binprm *, struct pt_regs *) = fmt->load_binary;
                  if (!fn)
                        continue;
                  if (!try_module_get(fmt->module))
                        continue;
                  read_unlock(&binfmt_lock);
                  retval = fn(bprm, regs);
                  /*
                   * Restore the depth counter to its starting value
                   * in this call, so we don't have to rely on every
                   * load_binary function to restore it on return.
                   */
                  bprm->recursion_depth = depth;
                  if (retval >= 0) {
                        if (depth == 0)
                              tracehook_report_exec(fmt, bprm, regs);
                        put_binfmt(fmt);
                        allow_write_access(bprm->file);
                        if (bprm->file)
                              fput(bprm->file);
                        bprm->file = NULL;
                        current->did_exec = 1;
                        proc_exec_connector(current);
                        return retval;
                  }
                  read_lock(&binfmt_lock);
                  put_binfmt(fmt);
                  if (retval != -ENOEXEC || bprm->mm == NULL)
                        break;
                  if (!bprm->file) {
                        read_unlock(&binfmt_lock);
                        return retval;
                  }
            }
            read_unlock(&binfmt_lock);
            if (retval != -ENOEXEC || bprm->mm == NULL) {
                  break;
#ifdef CONFIG_MODULES
            } else {
#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
                  if (printable(bprm->buf[0]) &&
                      printable(bprm->buf[1]) &&
                      printable(bprm->buf[2]) &&
                      printable(bprm->buf[3]))
                        break; /* -ENOEXEC */
                  request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
#endif
            }
      }
      return retval;
}

EXPORT_SYMBOL(search_binary_handler);

/*
 * sys_execve() executes a new program.
 */
int do_execve(const char * filename,
      const char __user *const __user *argv,
      const char __user *const __user *envp,
      struct pt_regs * regs)
{
      struct linux_binprm *bprm;
      struct file *file;
      struct files_struct *displaced;
      bool clear_in_exec;
      int retval;

      retval = unshare_files(&displaced);
      if (retval)
            goto out_ret;

      retval = -ENOMEM;
      bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
      if (!bprm)
            goto out_files;

      retval = prepare_bprm_creds(bprm);
      if (retval)
            goto out_free;

      retval = check_unsafe_exec(bprm);
      if (retval < 0)
            goto out_free;
      clear_in_exec = retval;
      current->in_execve = 1;

      file = open_exec(filename);
      retval = PTR_ERR(file);
      if (IS_ERR(file))
            goto out_unmark;

      sched_exec();

      bprm->file = file;
      bprm->filename = filename;
      bprm->interp = filename;

      retval = bprm_mm_init(bprm);
      if (retval)
            goto out_file;

      bprm->argc = count(argv, MAX_ARG_STRINGS);
      if ((retval = bprm->argc) < 0)
            goto out;

      bprm->envc = count(envp, MAX_ARG_STRINGS);
      if ((retval = bprm->envc) < 0)
            goto out;

      retval = prepare_binprm(bprm);
      if (retval < 0)
            goto out;

      retval = copy_strings_kernel(1, &bprm->filename, bprm);
      if (retval < 0)
            goto out;

      bprm->exec = bprm->p;
      retval = copy_strings(bprm->envc, envp, bprm);
      if (retval < 0)
            goto out;

      retval = copy_strings(bprm->argc, argv, bprm);
      if (retval < 0)
            goto out;

      retval = search_binary_handler(bprm,regs);
      if (retval < 0)
            goto out;

      /* execve succeeded */
      current->fs->in_exec = 0;
      current->in_execve = 0;
      acct_update_integrals(current);
      free_bprm(bprm);
      if (displaced)
            put_files_struct(displaced);
      return retval;

out:
      if (bprm->mm)
            mmput (bprm->mm);

out_file:
      if (bprm->file) {
            allow_write_access(bprm->file);
            fput(bprm->file);
      }

out_unmark:
      if (clear_in_exec)
            current->fs->in_exec = 0;
      current->in_execve = 0;

out_free:
      free_bprm(bprm);

out_files:
      if (displaced)
            reset_files_struct(displaced);
out_ret:
      return retval;
}

void set_binfmt(struct linux_binfmt *new)
{
      struct mm_struct *mm = current->mm;

      if (mm->binfmt)
            module_put(mm->binfmt->module);

      mm->binfmt = new;
      if (new)
            __module_get(new->module);
}

EXPORT_SYMBOL(set_binfmt);

static int expand_corename(struct core_name *cn)
{
      char *old_corename = cn->corename;

      cn->size = CORENAME_MAX_SIZE * atomic_inc_return(&call_count);
      cn->corename = krealloc(old_corename, cn->size, GFP_KERNEL);

      if (!cn->corename) {
            kfree(old_corename);
            return -ENOMEM;
      }

      return 0;
}

static int cn_printf(struct core_name *cn, const char *fmt, ...)
{
      char *cur;
      int need;
      int ret;
      va_list arg;

      va_start(arg, fmt);
      need = vsnprintf(NULL, 0, fmt, arg);
      va_end(arg);

      if (likely(need < cn->size - cn->used - 1))
            goto out_printf;

      ret = expand_corename(cn);
      if (ret)
            goto expand_fail;

out_printf:
      cur = cn->corename + cn->used;
      va_start(arg, fmt);
      vsnprintf(cur, need + 1, fmt, arg);
      va_end(arg);
      cn->used += need;
      return 0;

expand_fail:
      return ret;
}

/* format_corename will inspect the pattern parameter, and output a
 * name into corename, which must have space for at least
 * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 */
static int format_corename(struct core_name *cn, long signr)
{
      const struct cred *cred = current_cred();
      const char *pat_ptr = core_pattern;
      int ispipe = (*pat_ptr == '|');
      int pid_in_pattern = 0;
      int err = 0;

      cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
      cn->corename = kmalloc(cn->size, GFP_KERNEL);
      cn->used = 0;

      if (!cn->corename)
            return -ENOMEM;

      /* Repeat as long as we have more pattern to process and more output
         space */
      while (*pat_ptr) {
            if (*pat_ptr != '%') {
                  if (*pat_ptr == 0)
                        goto out;
                  err = cn_printf(cn, "%c", *pat_ptr++);
            } else {
                  switch (*++pat_ptr) {
                  /* single % at the end, drop that */
                  case 0:
                        goto out;
                  /* Double percent, output one percent */
                  case '%':
                        err = cn_printf(cn, "%c", '%');
                        break;
                  /* pid */
                  case 'p':
                        pid_in_pattern = 1;
                        err = cn_printf(cn, "%d",
                                    task_tgid_vnr(current));
                        break;
                  /* uid */
                  case 'u':
                        err = cn_printf(cn, "%d", cred->uid);
                        break;
                  /* gid */
                  case 'g':
                        err = cn_printf(cn, "%d", cred->gid);
                        break;
                  /* signal that caused the coredump */
                  case 's':
                        err = cn_printf(cn, "%ld", signr);
                        break;
                  /* UNIX time of coredump */
                  case 't': {
                        struct timeval tv;
                        do_gettimeofday(&tv);
                        err = cn_printf(cn, "%lu", tv.tv_sec);
                        break;
                  }
                  /* hostname */
                  case 'h':
                        down_read(&uts_sem);
                        err = cn_printf(cn, "%s",
                                    utsname()->nodename);
                        up_read(&uts_sem);
                        break;
                  /* executable */
                  case 'e':
                        err = cn_printf(cn, "%s", current->comm);
                        break;
                  /* core limit size */
                  case 'c':
                        err = cn_printf(cn, "%lu",
                                    rlimit(RLIMIT_CORE));
                        break;
                  default:
                        break;
                  }
                  ++pat_ptr;
            }

            if (err)
                  return err;
      }

      /* Backward compatibility with core_uses_pid:
       *
       * If core_pattern does not include a %p (as is the default)
       * and core_uses_pid is set, then .%pid will be appended to
       * the filename. Do not do this for piped commands. */
      if (!ispipe && !pid_in_pattern && core_uses_pid) {
            err = cn_printf(cn, ".%d", task_tgid_vnr(current));
            if (err)
                  return err;
      }
out:
      return ispipe;
}

static int zap_process(struct task_struct *start, int exit_code)
{
      struct task_struct *t;
      int nr = 0;

      start->signal->flags = SIGNAL_GROUP_EXIT;
      start->signal->group_exit_code = exit_code;
      start->signal->group_stop_count = 0;

      t = start;
      do {
            if (t != current && t->mm) {
                  sigaddset(&t->pending.signal, SIGKILL);
                  signal_wake_up(t, 1);
                  nr++;
            }
      } while_each_thread(start, t);

      return nr;
}

static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
                        struct core_state *core_state, int exit_code)
{
      struct task_struct *g, *p;
      unsigned long flags;
      int nr = -EAGAIN;

      spin_lock_irq(&tsk->sighand->siglock);
      if (!signal_group_exit(tsk->signal)) {
            mm->core_state = core_state;
            nr = zap_process(tsk, exit_code);
      }
      spin_unlock_irq(&tsk->sighand->siglock);
      if (unlikely(nr < 0))
            return nr;

      if (atomic_read(&mm->mm_users) == nr + 1)
            goto done;
      /*
       * We should find and kill all tasks which use this mm, and we should
       * count them correctly into ->nr_threads. We don't take tasklist
       * lock, but this is safe wrt:
       *
       * fork:
       *    None of sub-threads can fork after zap_process(leader). All
       *    processes which were created before this point should be
       *    visible to zap_threads() because copy_process() adds the new
       *    process to the tail of init_task.tasks list, and lock/unlock
       *    of ->siglock provides a memory barrier.
       *
       * do_exit:
       *    The caller holds mm->mmap_sem. This means that the task which
       *    uses this mm can't pass exit_mm(), so it can't exit or clear
       *    its ->mm.
       *
       * de_thread:
       *    It does list_replace_rcu(&leader->tasks, &current->tasks),
       *    we must see either old or new leader, this does not matter.
       *    However, it can change p->sighand, so lock_task_sighand(p)
       *    must be used. Since p->mm != NULL and we hold ->mmap_sem
       *    it can't fail.
       *
       *    Note also that "g" can be the old leader with ->mm == NULL
       *    and already unhashed and thus removed from ->thread_group.
       *    This is OK, __unhash_process()->list_del_rcu() does not
       *    clear the ->next pointer, we will find the new leader via
       *    next_thread().
       */
      rcu_read_lock();
      for_each_process(g) {
            if (g == tsk->group_leader)
                  continue;
            if (g->flags & PF_KTHREAD)
                  continue;
            p = g;
            do {
                  if (p->mm) {
                        if (unlikely(p->mm == mm)) {
                              lock_task_sighand(p, &flags);
                              nr += zap_process(p, exit_code);
                              unlock_task_sighand(p, &flags);
                        }
                        break;
                  }
            } while_each_thread(g, p);
      }
      rcu_read_unlock();
done:
      atomic_set(&core_state->nr_threads, nr);
      return nr;
}

static int coredump_wait(int exit_code, struct core_state *core_state)
{
      struct task_struct *tsk = current;
      struct mm_struct *mm = tsk->mm;
      struct completion *vfork_done;
      int core_waiters = -EBUSY;

      init_completion(&core_state->startup);
      core_state->dumper.task = tsk;
      core_state->dumper.next = NULL;

      down_write(&mm->mmap_sem);
      if (!mm->core_state)
            core_waiters = zap_threads(tsk, mm, core_state, exit_code);
      up_write(&mm->mmap_sem);

      if (unlikely(core_waiters < 0))
            goto fail;

      /*
       * Make sure nobody is waiting for us to release the VM,
       * otherwise we can deadlock when we wait on each other
       */
      vfork_done = tsk->vfork_done;
      if (vfork_done) {
            tsk->vfork_done = NULL;
            complete(vfork_done);
      }

      if (core_waiters)
            wait_for_completion(&core_state->startup);
fail:
      return core_waiters;
}

static void coredump_finish(struct mm_struct *mm)
{
      struct core_thread *curr, *next;
      struct task_struct *task;

      next = mm->core_state->dumper.next;
      while ((curr = next) != NULL) {
            next = curr->next;
            task = curr->task;
            /*
             * see exit_mm(), curr->task must not see
             * ->task == NULL before we read ->next.
             */
            smp_mb();
            curr->task = NULL;
            wake_up_process(task);
      }

      mm->core_state = NULL;
}

/*
 * set_dumpable converts traditional three-value dumpable to two flags and
 * stores them into mm->flags.  It modifies lower two bits of mm->flags, but
 * these bits are not changed atomically.  So get_dumpable can observe the
 * intermediate state.  To avoid doing unexpected behavior, get get_dumpable
 * return either old dumpable or new one by paying attention to the order of
 * modifying the bits.
 *
 * dumpable |   mm->flags (binary)
 * old  new | initial interim  final
 * ---------+-----------------------
 *  0    1  |   00      01      01
 *  0    2  |   00      10(*)   11
 *  1    0  |   01      00      00
 *  1    2  |   01      11      11
 *  2    0  |   11      10(*)   00
 *  2    1  |   11      11      01
 *
 * (*) get_dumpable regards interim value of 10 as 11.
 */
void set_dumpable(struct mm_struct *mm, int value)
{
      switch (value) {
      case 0:
            clear_bit(MMF_DUMPABLE, &mm->flags);
            smp_wmb();
            clear_bit(MMF_DUMP_SECURELY, &mm->flags);
            break;
      case 1:
            set_bit(MMF_DUMPABLE, &mm->flags);
            smp_wmb();
            clear_bit(MMF_DUMP_SECURELY, &mm->flags);
            break;
      case 2:
            set_bit(MMF_DUMP_SECURELY, &mm->flags);
            smp_wmb();
            set_bit(MMF_DUMPABLE, &mm->flags);
            break;
      }
}

static int __get_dumpable(unsigned long mm_flags)
{
      int ret;

      ret = mm_flags & MMF_DUMPABLE_MASK;
      return (ret >= 2) ? 2 : ret;
}

int get_dumpable(struct mm_struct *mm)
{
      return __get_dumpable(mm->flags);
}

static void wait_for_dump_helpers(struct file *file)
{
      struct pipe_inode_info *pipe;

      pipe = file->f_path.dentry->d_inode->i_pipe;

      pipe_lock(pipe);
      pipe->readers++;
      pipe->writers--;

      while ((pipe->readers > 1) && (!signal_pending(current))) {
            wake_up_interruptible_sync(&pipe->wait);
            kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
            pipe_wait(pipe);
      }

      pipe->readers--;
      pipe->writers++;
      pipe_unlock(pipe);

}


/*
 * uhm_pipe_setup
 * helper function to customize the process used
 * to collect the core in userspace.  Specifically
 * it sets up a pipe and installs it as fd 0 (stdin)
 * for the process.  Returns 0 on success, or
 * PTR_ERR on failure.
 * Note that it also sets the core limit to 1.  This
 * is a special value that we use to trap recursive
 * core dumps
 */
static int umh_pipe_setup(struct subprocess_info *info)
{
      struct file *rp, *wp;
      struct fdtable *fdt;
      struct coredump_params *cp = (struct coredump_params *)info->data;
      struct files_struct *cf = current->files;

      wp = create_write_pipe(0);
      if (IS_ERR(wp))
            return PTR_ERR(wp);

      rp = create_read_pipe(wp, 0);
      if (IS_ERR(rp)) {
            free_write_pipe(wp);
            return PTR_ERR(rp);
      }

      cp->file = wp;

      sys_close(0);
      fd_install(0, rp);
      spin_lock(&cf->file_lock);
      fdt = files_fdtable(cf);
      FD_SET(0, fdt->open_fds);
      FD_CLR(0, fdt->close_on_exec);
      spin_unlock(&cf->file_lock);

      /* and disallow core files too */
      current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};

      return 0;
}

void do_coredump(long signr, int exit_code, struct pt_regs *regs)
{
      struct core_state core_state;
      struct core_name cn;
      struct mm_struct *mm = current->mm;
      struct linux_binfmt * binfmt;
      const struct cred *old_cred;
      struct cred *cred;
      int retval = 0;
      int flag = 0;
      int ispipe;
      static atomic_t core_dump_count = ATOMIC_INIT(0);
      struct coredump_params cprm = {
            .signr = signr,
            .regs = regs,
            .limit = rlimit(RLIMIT_CORE),
            /*
             * We must use the same mm->flags while dumping core to avoid
             * inconsistency of bit flags, since this flag is not protected
             * by any locks.
             */
            .mm_flags = mm->flags,
      };

      audit_core_dumps(signr);

      binfmt = mm->binfmt;
      if (!binfmt || !binfmt->core_dump)
            goto fail;
      if (!__get_dumpable(cprm.mm_flags))
            goto fail;

      cred = prepare_creds();
      if (!cred)
            goto fail;
      /*
       *    We cannot trust fsuid as being the "true" uid of the
       *    process nor do we know its entire history. We only know it
       *    was tainted so we dump it as root in mode 2.
       */
      if (__get_dumpable(cprm.mm_flags) == 2) {
            /* Setuid core dump mode */
            flag = O_EXCL;          /* Stop rewrite attacks */
            cred->fsuid = 0;  /* Dump root private */
      }

      retval = coredump_wait(exit_code, &core_state);
      if (retval < 0)
            goto fail_creds;

      old_cred = override_creds(cred);

      /*
       * Clear any false indication of pending signals that might
       * be seen by the filesystem code called to write the core file.
       */
      clear_thread_flag(TIF_SIGPENDING);

      ispipe = format_corename(&cn, signr);

      if (ispipe == -ENOMEM) {
            printk(KERN_WARNING "format_corename failed\n");
            printk(KERN_WARNING "Aborting core\n");
            goto fail_corename;
      }

      if (ispipe) {
            int dump_count;
            char **helper_argv;

            if (cprm.limit == 1) {
                  /*
                   * Normally core limits are irrelevant to pipes, since
                   * we're not writing to the file system, but we use
                   * cprm.limit of 1 here as a speacial value. Any
                   * non-1 limit gets set to RLIM_INFINITY below, but
                   * a limit of 0 skips the dump.  This is a consistent
                   * way to catch recursive crashes.  We can still crash
                   * if the core_pattern binary sets RLIM_CORE =  !1
                   * but it runs as root, and can do lots of stupid things
                   * Note that we use task_tgid_vnr here to grab the pid
                   * of the process group leader.  That way we get the
                   * right pid if a thread in a multi-threaded
                   * core_pattern process dies.
                   */
                  printk(KERN_WARNING
                        "Process %d(%s) has RLIMIT_CORE set to 1\n",
                        task_tgid_vnr(current), current->comm);
                  printk(KERN_WARNING "Aborting core\n");
                  goto fail_unlock;
            }
            cprm.limit = RLIM_INFINITY;

            dump_count = atomic_inc_return(&core_dump_count);
            if (core_pipe_limit && (core_pipe_limit < dump_count)) {
                  printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
                         task_tgid_vnr(current), current->comm);
                  printk(KERN_WARNING "Skipping core dump\n");
                  goto fail_dropcount;
            }

            helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
            if (!helper_argv) {
                  printk(KERN_WARNING "%s failed to allocate memory\n",
                         __func__);
                  goto fail_dropcount;
            }

            retval = call_usermodehelper_fns(helper_argv[0], helper_argv,
                              NULL, UMH_WAIT_EXEC, umh_pipe_setup,
                              NULL, &cprm);
            argv_free(helper_argv);
            if (retval) {
                  printk(KERN_INFO "Core dump to %s pipe failed\n",
                         cn.corename);
                  goto close_fail;
            }
      } else {
            struct inode *inode;

            if (cprm.limit < binfmt->min_coredump)
                  goto fail_unlock;

            cprm.file = filp_open(cn.corename,
                         O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
                         0600);
            if (IS_ERR(cprm.file))
                  goto fail_unlock;

            inode = cprm.file->f_path.dentry->d_inode;
            if (inode->i_nlink > 1)
                  goto close_fail;
            if (d_unhashed(cprm.file->f_path.dentry))
                  goto close_fail;
            /*
             * AK: actually i see no reason to not allow this for named
             * pipes etc, but keep the previous behaviour for now.
             */
            if (!S_ISREG(inode->i_mode))
                  goto close_fail;
            /*
             * Dont allow local users get cute and trick others to coredump
             * into their pre-created files.
             */
            if (inode->i_uid != current_fsuid())
                  goto close_fail;
            if (!cprm.file->f_op || !cprm.file->f_op->write)
                  goto close_fail;
            if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
                  goto close_fail;
      }

      retval = binfmt->core_dump(&cprm);
      if (retval)
            current->signal->group_exit_code |= 0x80;

      if (ispipe && core_pipe_limit)
            wait_for_dump_helpers(cprm.file);
close_fail:
      if (cprm.file)
            filp_close(cprm.file, NULL);
fail_dropcount:
      if (ispipe)
            atomic_dec(&core_dump_count);
fail_unlock:
      kfree(cn.corename);
fail_corename:
      coredump_finish(mm);
      revert_creds(old_cred);
fail_creds:
      put_cred(cred);
fail:
      return;
}

/*
 * Core dumping helper functions.  These are the only things you should
 * do on a core-file: use only these functions to write out all the
 * necessary info.
 */
int dump_write(struct file *file, const void *addr, int nr)
{
      return access_ok(VERIFY_READ, addr, nr) && file->f_op->write(file, addr, nr, &file->f_pos) == nr;
}
EXPORT_SYMBOL(dump_write);

int dump_seek(struct file *file, loff_t off)
{
      int ret = 1;

      if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
            if (file->f_op->llseek(file, off, SEEK_CUR) < 0)
                  return 0;
      } else {
            char *buf = (char *)get_zeroed_page(GFP_KERNEL);

            if (!buf)
                  return 0;
            while (off > 0) {
                  unsigned long n = off;

                  if (n > PAGE_SIZE)
                        n = PAGE_SIZE;
                  if (!dump_write(file, buf, n)) {
                        ret = 0;
                        break;
                  }
                  off -= n;
            }
            free_page((unsigned long)buf);
      }
      return ret;
}
EXPORT_SYMBOL(dump_seek);

/*
 * check-name: Full text of fs/exec.c from Linux v2.6.37-rc1-542-g0143832
 * check-output-start
I: loaded rsf model for alpha
I: loaded rsf model for arm
I: loaded rsf model for avr32
I: loaded rsf model for blackfin
I: loaded rsf model for cris
I: loaded rsf model for frv
I: loaded rsf model for h8300
I: loaded rsf model for ia64
I: loaded rsf model for m32r
I: loaded rsf model for m68k
I: loaded rsf model for m68knommu
I: loaded rsf model for microblaze
I: loaded rsf model for mips
I: loaded rsf model for mn10300
I: loaded rsf model for parisc
I: loaded rsf model for powerpc
I: loaded rsf model for s390
I: loaded rsf model for score
I: loaded rsf model for sh
I: loaded rsf model for sparc
I: loaded rsf model for tile
I: loaded rsf model for x86
I: loaded rsf model for xtensa
I: found 23 rsf models
I: Using x86 as primary model
I: creating exec.c.B3.x86.missing.dead
I: creating exec.c.B11.x86.missing.dead
I: creating exec.c.B13.x86.missing.undead
I: creating exec.c.B16.x86.missing.dead
I: creating exec.c.B18.x86.missing.undead
 * check-output-end
 */

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