Subject: [PATCH 26/58] ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

From: Cong Wang <[email-masked]>
Date: Sun, 30 Dec 2018 12:43:42 -0800

[ Upstream commit aff6db454599d62191aabc208930e891748e4322 ]

__ptr_ring_swap_queue() tries to move pointers from the old
ring to the new one, but it forgets to check if ->producer
is beyond the new size at the end of the operation. This leads
to an out-of-bound access in __ptr_ring_produce() as reported
by syzbot.

Reported-by: [email-masked]
Fixes: 5d49de532002 ("ptr_ring: resize support")
Cc: "Michael S. Tsirkin" <[email-masked]>
Cc: John Fastabend <[email-masked]>
Cc: Jason Wang <[email-masked]>
Signed-off-by: Cong Wang <[email-masked]>
Acked-by: Michael S. Tsirkin <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 include/linux/ptr_ring.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 6894976b54e3..186cd8e970c7 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -573,6 +573,8 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
 		else if (destroy)
 			destroy(ptr);
 
+	if (producer >= size)
+		producer = 0;
 	__ptr_ring_set_size(r, size);
 	r->producer = producer;
 	r->consumer_head = 0;
-- 
2.20.1