[PATCH] dccp: fix freeing skb too early for IPV6_RECVPKTINFO

[PATCH] dccp: fix freeing skb too early for IPV6_RECVPKTINFO

[Andrey Konovalov]

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@google.com>
---
 net/dccp/input.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/dccp/input.c b/net/dccp/input.c
index ba347184bda9..8fedc2d49770 100644
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -606,7 +606,8 @@ int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 			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;
-- 
2.11.0.483.g087da7b7c-goog

Re: [PATCH] dccp: fix freeing skb too early for IPV6_RECVPKTINFO

[Eric Dumazet]

On Thu, 2017-02-16 at 17:22 +0100, Andrey Konovalov wrote:
> 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.
> 
> 			goto discard;

Thanks a lot Andrey !

Acked-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH] dccp: fix freeing skb too early for IPV6_RECVPKTINFO

[David Miller]

From: Andrey Konovalov <andreyknvl@google.com>
Date: Thu, 16 Feb 2017 17:22:46 +0100

> 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@google.com>

Applied and queued up for -stable, thanks.