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[PATCH] sanitize unshare_files/reset_files_struct

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* let unshare_files() give caller the displaced files_struct
* don't bother with grabbing reference only to drop it in the
  caller if it hadn't been shared in the first place
* in that form unshare_files() is trivially implemented via
  unshare_fd(), so we eliminate the duplicate logics in fork.c
* reset_files_struct() is not just only called for current;
  it will break the system if somebody ever calls it for anything
  else (we can't modify ->files of somebody else).  Lose the
  task_struct * argument.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2008-04-22 05:31:30 -04:00
parent fd8328be87
commit 3b1253880b
5 changed files with 34 additions and 47 deletions
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54
kernel/fork.c
View file

@ -840,36 +840,6 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
return 0;
}
/*
* Helper to unshare the files of the current task.
* We don't want to expose copy_files internals to
* the exec layer of the kernel.
*/
int unshare_files(void)
{
struct files_struct *files = current->files;
struct files_struct *newf;
int error = 0;
BUG_ON(!files);
/* This can race but the race causes us to copy when we don't
need to and drop the copy */
if(atomic_read(&files->count) == 1)
{
atomic_inc(&files->count);
return 0;
}
newf = dup_fd(files, &error);
if (newf) {
task_lock(current);
current->files = newf;
task_unlock(current);
}
return error;
}
static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
{
struct sighand_struct *sig;
@ -1807,3 +1777,27 @@ bad_unshare_cleanup_thread:
bad_unshare_out:
return err;
}
/*
* Helper to unshare the files of the current task.
* We don't want to expose copy_files internals to
* the exec layer of the kernel.
*/
int unshare_files(struct files_struct **displaced)
{
struct task_struct *task = current;
struct files_struct *copy;
int error;
error = unshare_fd(CLONE_FILES, &copy);
if (error || !copy) {
*displaced = NULL;
return error;
}
*displaced = task->files;
task_lock(task);
task->files = copy;
task_unlock(task);
return 0;
}