diff mbox series

[5.16,108/121] watch_queue: Fix to always request a pow-of-2 pipe ring size

Message ID 20220314112747.124927943@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

gregkh@linuxfoundation.org March 14, 2022, 11:54 a.m. UTC 
From: David Howells <dhowells@redhat.com>

commit 96a4d8912b28451cd62825fd7caa0e66e091d938 upstream.

The pipe ring size must always be a power of 2 as the head and tail
pointers are masked off by AND'ing with the size of the ring - 1.
watch_queue_set_size(), however, lets you specify any number of notes
between 1 and 511.  This number is passed through to pipe_resize_ring()
without checking/forcing its alignment.

Fix this by rounding the number of slots required up to the nearest
power of two.  The request is meant to guarantee that at least that many
notifications can be generated before the queue is full, so rounding
down isn't an option, but, alternatively, it may be better to give an
error if we aren't allowed to allocate that much ring space.

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>
---
 kernel/watch_queue.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -244,7 +244,7 @@  long watch_queue_set_size(struct pipe_in
 		goto error;
 	}
 
-	ret = pipe_resize_ring(pipe, nr_notes);
+	ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes));
 	if (ret < 0)
 		goto error;