netdev - [Patch net] ptr_ring: wrap back ->producer in __ptr_ring_swap

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Message-Id: <20181230204342.22699-1-xiyou.wangcong@gmail.com>
Date:   Sun, 30 Dec 2018 12:43:42 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jason Wang <jasowang@...hat.com>
Subject: [Patch net] ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

__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@...kaller.appspotmail.com
Fixes: 5d49de532002 ("ptr_ring: resize support")
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Jason Wang <jasowang@...hat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.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