Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain; charset="UTF-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Christoph Paasch" <cpaasch@apple.com>,
        "David S. Miller" <davem@davemloft.net>,
        "Eric Dumazet" <edumazet@google.com>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
Message-ID: <lsq.1519831218.554100668@decadent.org.uk>
Subject: [PATCH 3.16 090/254] tcp md5sig: Use skb's saddr when replying to
 an incoming segment
In-Reply-To: <lsq.1519831217.271785318@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

From: Christoph Paasch <cpaasch@apple.com>

commit 30791ac41927ebd3e75486f9504b6d2280463bf0 upstream.

The MD5-key that belongs to a connection is identified by the peer's
IP-address. When we are in tcp_v4(6)_reqsk_send_ack(), we are replying
to an incoming segment from tcp_check_req() that failed the seq-number
checks.

Thus, to find the correct key, we need to use the skb's saddr and not
the daddr.

This bug seems to have been there since quite a while, but probably got
unnoticed because the consequences are not catastrophic. We will call
tcp_v4_reqsk_send_ack only to send a challenge-ACK back to the peer,
thus the connection doesn't really fail.

Fixes: 9501f9722922 ("tcp md5sig: Let the caller pass appropriate key for tcp_v{4,6}_do_calc_md5_hash().")
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/ipv4/tcp_ipv4.c | 2 +-
 net/ipv6/tcp_ipv6.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -809,7 +809,7 @@ static void tcp_v4_reqsk_send_ack(struct
 			tcp_time_stamp,
 			req->ts_recent,
 			0,
-			tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,
+			tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->saddr,
 					  AF_INET),
 			inet_rsk(req)->no_srccheck ? IP_REPLY_ARG_NOSRCCHECK : 0,
 			ip_hdr(skb)->tos);
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -941,7 +941,7 @@ static void tcp_v6_reqsk_send_ack(struct
 			tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,
 			tcp_rsk(req)->rcv_nxt,
 			req->rcv_wnd, tcp_time_stamp, req->ts_recent, sk->sk_bound_dev_if,
-			tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->daddr),
+			tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->saddr),
 			0, 0);
 }