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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, syzbot <syzkaller@googlegroups.com>,
        Willem de Bruijn <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH 4.19 12/51] packet: unconditionally free po->rollover
Date:   Sun,  9 Jun 2019 18:41:53 +0200
Message-Id: <20190609164127.826684331@linuxfoundation.org>
In-Reply-To: <20190609164127.123076536@linuxfoundation.org>
References: <20190609164127.123076536@linuxfoundation.org>
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From: Willem de Bruijn <willemb@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 <syzkaller@googlegroups.com>
Diagnosed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@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
@@ -3017,8 +3017,8 @@ static int packet_release(struct socket
 
 	synchronize_net();
 
+	kfree(po->rollover);
 	if (f) {
-		kfree(po->rollover);
 		fanout_release_data(f);
 		kfree(f);
 	}