[PATCH 5.1 09/70] packet: unconditionally free po->rollover

[Greg Kroah-Hartman]

From: Willem de Bruijn <will...@google.com>

[ Upstream commit afa0925c6fcc6a8f610e996ca09bc3215048033c ]

Rollover used to use a complex RCU mechanism for assignment, which had
a race condition. The below patch fixed the bug and greatly simplified
the logic.

The feature depends on fanout, but the state is private to the socket.
Fanout_release returns f only when the last member leaves and the
fanout struct is to be freed.

Destroy rollover unconditionally, regardless of fanout state.

Fixes: 57f015f5eccf2 ("packet: fix crash in fanout_demux_rollover()")
Reported-by: syzbot <syzkal...@googlegroups.com>
Diagnosed-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/packet/af_packet.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3016,8 +3016,8 @@ static int packet_release(struct socket
 
        synchronize_net();
 
+       kfree(po->rollover);
        if (f) {
-               kfree(po->rollover);
                fanout_release_data(f);
                kfree(f);
        }