netdev - [PATCH net] packet: unconditionally free po->rollover

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Message-Id: <20190531163723.191617-1-willemdebruijn.kernel@gmail.com>
Date:   Fri, 31 May 2019 12:37:23 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, Willem de Bruijn <willemb@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH net] packet: unconditionally free po->rollover

From: Willem de Bruijn <willemb@...gle.com>

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 <syzkaller@...glegroups.com>
Diagnosed-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 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 fbc775fbf7128..d4889bf7248e1 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3014,8 +3014,8 @@ static int packet_release(struct socket *sock)
 
 	synchronize_net();
 
+	kfree(po->rollover);
 	if (f) {
-		kfree(po->rollover);
 		fanout_release_data(f);
 		kfree(f);
 	}
-- 
2.22.0.rc1.257.g3120a18244-goog