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Commit 5b0c1dd3 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Linus Torvalds
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[PATCH] proc: optimize proc_check_dentry_visible 



The code doesn't need to sleep to when making this check so I can just do the
comparison and not worry about the reference counts.

TODO: While looking at this I realized that my original cleanup did not push
the permission check far enough down into the stack.  The call of
proc_check_dentry_visible needs to move out of the generic proc
readlink/follow link code and into the individual get_link instances.
Otherwise the shared resources checks are not quite correct (shared
files_struct does not require a shared fs_struct), and there are races with
unshare.

Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 13b41b09

fs/proc/base.c

+16 −13
Original line number Diff line number Diff line
@@ -1074,24 +1074,27 @@ static int proc_check_dentry_visible(struct inode *inode, 
	 * namespace, or are simply process local (like pipes).

	 */

	struct task_struct *task;

	struct files_struct *task_files, *files;

	int error = -EACCES;



	/* See if the the two tasks share a commone set of

	 * file descriptors.  If so everything is visible.

	 */

	task = get_proc_task(inode);

	if (!task)

		goto out;

	files = get_files_struct(current);

	task_files = get_files_struct(task);

	if (files && task_files && (files == task_files))

	rcu_read_lock();

	task = tref_task(proc_tref(inode));

	if (task) {

		struct files_struct *task_files, *files;

		/* This test answeres the question:

		 * Is there a point in time since we looked up the

		 * file descriptor where the two tasks share the

		 * same files struct?

		 */

		rmb();

		files = current->files;

		task_files = task->files;

		if (files && (files == task_files))

			error = 0;

	if (task_files)

		put_files_struct(task_files);

	if (files)

		put_files_struct(files);

	put_task_struct(task);

	}

	rcu_read_unlock();

	if (!error)

		goto out;