Subject: [PATCH 13/18] packet: unconditionally free po->rollover

From: Willem de Bruijn <[email-masked]>
Date: Fri, 31 May 2019 12:37:23 -0400

[ 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 <[email-masked]>
Diagnosed-by: Dmitry Vyukov <[email-masked]>
Signed-off-by: Willem de Bruijn <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/packet/af_packet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 18df3bce73da..d98fcf926166 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3017,8 +3017,8 @@ static int packet_release(struct socket *sock)
 
 	synchronize_net();
 
+	kfree(po->rollover);
 	if (f) {
-		kfree(po->rollover);
 		fanout_release_data(f);
 		kfree(f);
 	}
-- 
2.20.1