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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+f99ab3887ab65d70f816@syzkaller.appspotmail.com,
        "Alexey Kodanev" <alexey.kodanev@oracle.com>,
        "David S. Miller" <davem@davemloft.net>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.209117817@decadent.org.uk>
Subject: [PATCH 3.16 021/410] dccp: check sk for closed state in
 dccp_sendmsg()
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Alexey Kodanev <alexey.kodanev@oracle.com>

commit 67f93df79aeefc3add4e4b31a752600f834236e2 upstream.

dccp_disconnect() sets 'dp->dccps_hc_tx_ccid' tx handler to NULL,
therefore if DCCP socket is disconnected and dccp_sendmsg() is
called after it, it will cause a NULL pointer dereference in
dccp_write_xmit().

This crash and the reproducer was reported by syzbot. Looks like
it is reproduced if commit 69c64866ce07 ("dccp: CVE-2017-8824:
use-after-free in DCCP code") is applied.

Reported-by: syzbot+f99ab3887ab65d70f816@syzkaller.appspotmail.com
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/dccp/proto.c | 5 +++++
 1 file changed, 5 insertions(+)

--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -785,6 +785,11 @@ int dccp_sendmsg(struct kiocb *iocb, str
 	if (skb == NULL)
 		goto out_release;
 
+	if (sk->sk_state == DCCP_CLOSED) {
+		rc = -ENOTCONN;
+		goto out_discard;
+	}
+
 	skb_reserve(skb, sk->sk_prot->max_header);
 	rc = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
 	if (rc != 0)