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

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

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.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@googlegroups.com>
Diagnosed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.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

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

[David Miller]

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Fri, 31 May 2019 12:37:23 -0400

> From: Willem de Bruijn <willemb@google.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@googlegroups.com>
> Diagnosed-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Applied and queued up for -stable.