[Patch net] ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

[Cong Wang]

__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+8993c0fa96d57c399...@syzkaller.appspotmail.com
Fixes: 5d49de532002 ("ptr_ring: resize support")
Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: John Fastabend <john.fastab...@gmail.com>
Cc: Jason Wang <jasow...@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 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;
-- 
2.19.2