From: David Howells dhowells@redhat.com
commit 2ed147f015af2b48f41c6f0b6746aa9ea85c19f3 upstream.
There's nothing to synchronise post_one_notification() versus pipe_read(). Whilst posting is done under pipe->rd_wait.lock, the reader only takes pipe->mutex which cannot bar notification posting as that may need to be made from contexts that cannot sleep.
Fix this by setting pipe->head with a barrier in post_one_notification() and reading pipe->head with a barrier in pipe_read().
If that's not sufficient, the rd_wait.lock will need to be taken, possibly in a ->confirm() op so that it only applies to notifications. The lock would, however, have to be dropped before copy_page_to_iter() is invoked.
Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-by: Jann Horn jannh@google.com Signed-off-by: David Howells dhowells@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/pipe.c | 3 ++- kernel/watch_queue.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-)
--- a/fs/pipe.c +++ b/fs/pipe.c @@ -252,7 +252,8 @@ pipe_read(struct kiocb *iocb, struct iov */ was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage); for (;;) { - unsigned int head = pipe->head; + /* Read ->head with a barrier vs post_one_notification() */ + unsigned int head = smp_load_acquire(&pipe->head); unsigned int tail = pipe->tail; unsigned int mask = pipe->ring_size - 1;
--- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -113,7 +113,7 @@ static bool post_one_notification(struct buf->offset = offset; buf->len = len; buf->flags = PIPE_BUF_FLAG_WHOLE; - pipe->head = head + 1; + smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */
if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { spin_unlock_irq(&pipe->rd_wait.lock);