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.
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
---
v2: Use reverse-christmas-tree local variable ordering.
diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h
index 1060494ac230..b8c86ec1a8f5 100644
--- a/include/net/sctp/ulpevent.h
+++ b/include/net/sctp/ulpevent.h
@@ -153,8 +153,12 @@ __u16 sctp_ulpevent_get_notification_type(const struct sctp_ulpevent *event);
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? */
--
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