linux-kernel - [PATCH 3.16 11/12] dccp: fix freeing skb too early for IPV6

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Message-ID: <lsq.1487938201.934279598@decadent.org.uk>
Date:   Fri, 24 Feb 2017 12:10:01 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Andrey Konovalov" <andreyknvl@...gle.com>
Subject: [PATCH 3.16 11/12] dccp: fix freeing skb too early for
 IPV6_RECVPKTINFO

3.16.41-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Konovalov <andreyknvl@...gle.com>

commit 5edabca9d4cff7f1f2b68f0bac55ef99d9798ba4 upstream.

In the current DCCP implementation an skb for a DCCP_PKT_REQUEST packet
is forcibly freed via __kfree_skb in dccp_rcv_state_process if
dccp_v6_conn_request successfully returns.

However, if IPV6_RECVPKTINFO is set on a socket, the address of the skb
is saved to ireq->pktopts and the ref count for skb is incremented in
dccp_v6_conn_request, so skb is still in use. Nevertheless, it gets freed
in dccp_rcv_state_process.

Fix by calling consume_skb instead of doing goto discard and therefore
calling __kfree_skb.

Similar fixes for TCP:

fb7e2399ec17f1004c0e0ccfd17439f8759ede01 [TCP]: skb is unexpectedly freed.
0aea76d35c9651d55bbaf746e7914e5f9ae5a25d tcp: SYN packets are now
simply consumed

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/dccp/input.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -606,7 +606,8 @@ int dccp_rcv_state_process(struct sock *
 			if (inet_csk(sk)->icsk_af_ops->conn_request(sk,
 								    skb) < 0)
 				return 1;
-			goto discard;
+			consume_skb(skb);
+			return 0;
 		}
 		if (dh->dccph_type == DCCP_PKT_RESET)
 			goto discard;