From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 10 Dec 2017 15:40:51 +0800
Subject: sctp: make sure stream nums can match optlen in sctp_setsockopt_reset_streams
Patch-mainline: v4.15-rc4
Git-commit: 2342b8d95bcae5946e1b9b8d58645f37500ef2e7
References: bsc#1076830

Now in sctp_setsockopt_reset_streams, it only does the check
optlen < sizeof(*params) for optlen. But it's not enough, as
params->srs_number_streams should also match optlen.

If the streams in params->srs_stream_list are less than stream
nums in params->srs_number_streams, later when dereferencing
the stream list, it could cause a slab-out-of-bounds crash, as
reported by syzbot.

This patch is to fix it by also checking the stream numbers in
sctp_setsockopt_reset_streams to make sure at least it's not
greater than the streams in the list.

Fixes: 7f9d68ac944e ("sctp: implement sender-side procedures for SSN Reset Request Parameter")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/sctp/socket.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 19630459712d..26b3de0d826f 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3835,13 +3835,17 @@ static int sctp_setsockopt_reset_streams(struct sock *sk,
 	struct sctp_association *asoc;
 	int retval = -EINVAL;
 
-	if (optlen < sizeof(struct sctp_reset_streams))
+	if (optlen < sizeof(*params))
 		return -EINVAL;
 
 	params = memdup_user(optval, optlen);
 	if (IS_ERR(params))
 		return PTR_ERR(params);
 
+	if (params->srs_number_streams * sizeof(__u16) >
+	    optlen - sizeof(*params))
+		goto out;
+
 	asoc = sctp_id2assoc(sk, params->srs_assoc_id);
 	if (!asoc)
 		goto out;
-- 
2.15.1