[PATCH net v4] sctp: fix a potential OOB access in sctp_sched_set_sched()

[Gavrilov Ilia]

The 'sched' index value must be checked before accessing an element
of the 'sctp_sched_ops' array. Otherwise, it can lead to OOB access.

Note that it's harmless since the 'sched' parameter is checked before
calling 'sctp_sched_set_sched'.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Reviewed-by: Xin Long <lucien.xin@xxxxxxxxx>
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@xxxxxxxxxxx>
---
V2:
 - Change the order of local variables 
 - Specify the target tree in the subject
V3:
 - Change description
 - Remove 'fixes'
V4:
 - revert to V2
 net/sctp/stream_sched.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/sctp/stream_sched.c b/net/sctp/stream_sched.c
index 330067002deb..4d076a9b8592 100644
--- a/net/sctp/stream_sched.c
+++ b/net/sctp/stream_sched.c
@@ -146,18 +146,19 @@ static void sctp_sched_free_sched(struct sctp_stream *stream)
 int sctp_sched_set_sched(struct sctp_association *asoc,
 			 enum sctp_sched_type sched)
 {
-	struct sctp_sched_ops *n = sctp_sched_ops[sched];
 	struct sctp_sched_ops *old = asoc->outqueue.sched;
 	struct sctp_datamsg *msg = NULL;
+	struct sctp_sched_ops *n;
 	struct sctp_chunk *ch;
 	int i, ret = 0;
 
-	if (old == n)
-		return ret;
-
 	if (sched > SCTP_SS_MAX)
 		return -EINVAL;
 
+	n = sctp_sched_ops[sched];
+	if (old == n)
+		return ret;
+
 	if (old)
 		sctp_sched_free_sched(&asoc->stream);
 
-- 
2.30.2