From db8facfc9fafacefe8a835416a6b77c838088f8b Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 11 Mar 2022 13:23:38 +0000 Subject: watch_queue, pipe: Free watchqueue state after clearing pipe ring In free_pipe_info(), free the watchqueue state after clearing the pipe ring as each pipe ring descriptor has a release function, and in the case of a notification message, this is watch_queue_pipe_buf_release() which tries to mark the allocation bitmap that was previously released. Fix this by moving the put of the pipe's ref on the watch queue to after the ring has been cleared. We still need to call watch_queue_clear() before doing that to make sure that the pipe is disconnected from any notification sources first. Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-by: Jann Horn Signed-off-by: David Howells Signed-off-by: Linus Torvalds --- fs/pipe.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'fs/pipe.c') diff --git a/fs/pipe.c b/fs/pipe.c index cc28623a67b6..4eb88bc138bb 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -831,10 +831,8 @@ void free_pipe_info(struct pipe_inode_info *pipe) int i; #ifdef CONFIG_WATCH_QUEUE - if (pipe->watch_queue) { + if (pipe->watch_queue) watch_queue_clear(pipe->watch_queue); - put_watch_queue(pipe->watch_queue); - } #endif (void) account_pipe_buffers(pipe->user, pipe->nr_accounted, 0); @@ -844,6 +842,10 @@ void free_pipe_info(struct pipe_inode_info *pipe) if (buf->ops) pipe_buf_release(pipe, buf); } +#ifdef CONFIG_WATCH_QUEUE + if (pipe->watch_queue) + put_watch_queue(pipe->watch_queue); +#endif if (pipe->tmp_page) __free_page(pipe->tmp_page); kfree(pipe->bufs); -- cgit v1.2.3-70-g09d2 From 2ed147f015af2b48f41c6f0b6746aa9ea85c19f3 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 11 Mar 2022 13:24:36 +0000 Subject: watch_queue: Fix lack of barrier/sync/lock between post and read 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 Signed-off-by: David Howells Signed-off-by: Linus Torvalds --- fs/pipe.c | 3 ++- kernel/watch_queue.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) (limited to 'fs/pipe.c') diff --git a/fs/pipe.c b/fs/pipe.c index 4eb88bc138bb..2667db9506e2 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -253,7 +253,8 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) */ 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; diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index c12267ccc70e..37bcd900fd77 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -113,7 +113,7 @@ static bool post_one_notification(struct watch_queue *wqueue, 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); -- cgit v1.2.3-70-g09d2