Commit 9e6b7cd7 authored Sep 17, 2015 by Dmitry Vyukov Committed by Greg Kroah-Hartman Oct 04, 2015

tty: fix data race in tty_buffer_flush



tty_buffer_flush frees not acquired buffers.
As the result, for example, read of b->size in tty_buffer_free
can return garbage value which will lead to a huge buffer
hanging in the freelist. This is just the benignest
manifestation of freeing of a not acquired object.
If the object is passed to kfree, heap can be corrupted.

Acquire visibility over the buffer before freeing it.

The data race was found with KernelThreadSanitizer (KTSAN).

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 7098296a

drivers/tty/tty_buffer.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -242,7 +242,10 @@ void tty_buffer_flush(struct tty_struct tty, struct tty_ldisc ld)
		atomic_inc(&buf->priority);

		mutex_lock(&buf->lock);
		while ((next = buf->head->next) != NULL) {
		/* paired w/ release in __tty_buffer_request_room; ensures there are
		* no pending memory accesses to the freed buffer
		*/
		while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
		tty_buffer_free(port, buf->head);
		buf->head = next;
		}

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