ptr_ring: wrap back ->producer in __ptr_ring_swap_queue()

BugLink: https://bugs.launchpad.net/bugs/1837257
[ 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@syzkaller.appspotmail.com
Fixes: 5d49de532002 ("ptr_ring: resize support")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index d0bd988aff7082db32bf05dde7bfb3b8f506342c..ed65d6628941c313904cbe43dcd32364185532ed 100644 (file)
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -557,6 +557,8 @@ 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;