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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        syzbot+7b7b518b1228d2743963@syzkaller.appspotmail.com,
        "Marcelo Ricardo Leitner" <marcelo.leitner@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        "Neil Horman" <nhorman@tuxdriver.com>,
        "Xin Long" <lucien.xin@gmail.com>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
Message-ID: <lsq.1519831218.624177862@decadent.org.uk>
Subject: [PATCH 3.16 211/254] sctp: do not allow the v4 socket to bind a
 v4mapped v6 address
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: Xin Long <lucien.xin@gmail.com>

commit c5006b8aa74599ce19104b31d322d2ea9ff887cc upstream.

The check in sctp_sockaddr_af is not robust enough to forbid binding a
v4mapped v6 addr on a v4 socket.

The worse thing is that v4 socket's bind_verify would not convert this
v4mapped v6 addr to a v4 addr. syzbot even reported a crash as the v4
socket bound a v6 addr.

This patch is to fix it by doing the common sa.sa_family check first,
then AF_INET check for v4mapped v6 addrs.

Fixes: 7dab83de50c7 ("sctp: Support ipv6only AF_INET6 sockets.")
Reported-by: syzbot+7b7b518b1228d2743963@syzkaller.appspotmail.com
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/sctp/socket.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -303,16 +303,14 @@ static struct sctp_af *sctp_sockaddr_af(
 	if (len < sizeof (struct sockaddr))
 		return NULL;
 
+	if (!opt->pf->af_supported(addr->sa.sa_family, opt))
+		return NULL;
+
 	/* V4 mapped address are really of AF_INET family */
 	if (addr->sa.sa_family == AF_INET6 &&
-	    ipv6_addr_v4mapped(&addr->v6.sin6_addr)) {
-		if (!opt->pf->af_supported(AF_INET, opt))
-			return NULL;
-	} else {
-		/* Does this PF support this AF? */
-		if (!opt->pf->af_supported(addr->sa.sa_family, opt))
-			return NULL;
-	}
+	    ipv6_addr_v4mapped(&addr->v6.sin6_addr) &&
+	    !opt->pf->af_supported(AF_INET, opt))
+		return NULL;
 
 	/* If we get this far, af is valid. */
 	af = sctp_get_af_specific(addr->sa.sa_family);