Unverified Commit f13abc1e authored by Eric Sandeen's avatar Eric Sandeen Committed by Christian Brauner
Browse files

watch_queue: fix pipe accounting mismatch 



Currently, watch_queue_set_size() modifies the pipe buffers charged to
user->pipe_bufs without updating the pipe->nr_accounted on the pipe
itself, due to the if (!pipe_has_watch_queue()) test in
pipe_resize_ring(). This means that when the pipe is ultimately freed,
we decrement user->pipe_bufs by something other than what than we had
charged to it, potentially leading to an underflow. This in turn can
cause subsequent too_many_pipe_buffers_soft() tests to fail with -EPERM.

To remedy this, explicitly account for the pipe usage in
watch_queue_set_size() to match the number set via account_pipe_buffers()

(It's unclear why watch_queue_set_size() does not update nr_accounted;
it may be due to intentional overprovisioning in watch_queue_set_size()?)

Fixes: e95aada4 ("pipe: wakeup wr_wait after setting max_usage")
Signed-off-by: default avatarEric Sandeen <sandeen@redhat.com>
Link: https://lore.kernel.org/r/206682a8-0604-49e5-8224-fdbe0c12b460@redhat.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent e249056c

kernel/watch_queue.c

+9 −0
Original line number Diff line number Diff line
@@ -269,6 +269,15 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) 
	if (ret < 0)

		goto error;



	/*

	 * pipe_resize_ring() does not update nr_accounted for watch_queue

	 * pipes, because the above vastly overprovisions. Set nr_accounted on

	 * and max_usage this pipe to the number that was actually charged to

	 * the user above via account_pipe_buffers.

	 */

	pipe->max_usage = nr_pages;

	pipe->nr_accounted = nr_pages;



	ret = -ENOMEM;

	pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);

	if (!pages)