Patch "sctp: potential read out of bounds in sctp_ulpevent_type_enabled()" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

sctp: potential read out of bounds in sctp_ulpevent_type_enabled()

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sctp-potential-read-out-of-bounds-in-sctp_ulpevent_type_enabled.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dan Carpenter <[email protected]>
Date: Thu, 14 Sep 2017 02:00:54 +0300
Subject: sctp: potential read out of bounds in sctp_ulpevent_type_enabled()

From: Dan Carpenter <[email protected]>

[ Upstream commit fa5f7b51fc3080c2b195fa87c7eca7c05e56f673 ]

This code causes a static checker warning because Smatch doesn't trust anything that comes from skb->data. I've reviewed this code and I do think skb->data can be controlled by the user here.

The sctp_event_subscribe struct has 13 __u8 fields and we want to see if ours is non-zero. sn_type can be any value in the 0-USHRT_MAX range. We're subtracting SCTP_SN_TYPE_BASE which is 1 << 15 so we could read either before the start of the struct or after the end.

This is a very old bug and it's surprising that it would go undetected for so long but my theory is that it just doesn't have a big impact so it would be hard to notice.

---
 include/net/sctp/ulpevent.h |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -141,8 +141,12 @@ __u16 sctp_ulpevent_get_notification_typ
 static inline int sctp_ulpevent_type_enabled(__u16 sn_type,
 					     struct sctp_event_subscribe *mask)
 {
+	int offset = sn_type - SCTP_SN_TYPE_BASE;
 	char *amask = (char *) mask;
-	return amask[sn_type - SCTP_SN_TYPE_BASE];
+
+	if (offset >= sizeof(struct sctp_event_subscribe))
+		return 0;
+	return amask[offset];
 }
 
 /* Given an event subscription, is this event enabled? */

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/sctp-potential-read-out-of-bounds-in-sctp_ulpevent_type_enabled.patch