[PATCH net] sctp: make sure stream nums can match optlen in sctp_setsockopt_reset_streams

[Xin Long]

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 <dvyu...@google.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 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 014847e..dbf140d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3891,13 +3891,17 @@ 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;
-- 
2.1.0