linux-kernel - [PATCH 4.20 017/145] ptr_ring: wrap back ->producer in __ptr_ring_swap

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Date:   Mon,  7 Jan 2019 13:30:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+8993c0fa96d57c399735@...kaller.appspotmail.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jason Wang <jasowang@...hat.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.20 017/145] ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

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

------------------

From: Cong Wang <xiyou.wangcong@...il.com>

[ 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@...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>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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)
 			destroy(ptr);
 
+	if (producer >= size)
+		producer = 0;
 	__ptr_ring_set_size(r, size);
 	r->producer = producer;
 	r->consumer_head = 0;