netdev - [PATCH net] dccp: check sk for closed state in dccp

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Message-Id: <1520366221-12350-1-git-send-email-alexey.kodanev@oracle.com>
Date:   Tue,  6 Mar 2018 22:57:01 +0300
From:   Alexey Kodanev <alexey.kodanev@...cle.com>
To:     netdev@...r.kernel.org
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kodanev <alexey.kodanev@...cle.com>
Subject: [PATCH net] dccp: check sk for closed state in dccp_sendmsg()

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@...kaller.appspotmail.com
Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>
---
 net/dccp/proto.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 15bdc00..84cd4e3 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -794,6 +794,11 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	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_from_msg(skb_put(skb, len), msg, len);
 	if (rc != 0)
-- 
1.8.3.1