[PATCH 4.19 026/170] ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

From: Greg Kroah-Hartman
Date: Mon Jan 07 2019 - 07:49:15 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

[ 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: syzbot+8993c0fa96d57c399735@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 5d49de532002 ("ptr_ring: resize support")
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
include/linux/ptr_ring.h | 2 ++
1 file changed, 2 insertions(+)

--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -573,6 +573,8 @@ static inline void **__ptr_ring_swap_que
else if (destroy)

+ if (producer >= size)
+ producer = 0;
__ptr_ring_set_size(r, size);
r->producer = producer;
r->consumer_head = 0;