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@syzkaller.appspotmail.com
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 @@
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)