[PATCH] tty: fix data race in tty_buffer_flush

From: Dmitry Vyukov
Date: Mon Sep 07 2015 - 08:26:32 EST

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@xxxxxxxxxx>
drivers/tty/tty_buffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 5a3fa89..7dab1b3 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -242,7 +242,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)

- while ((next = buf->head->next) != NULL) {
+ while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/