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sctp: potential read out of bounds in sctp_ulpevent_type_enabled()

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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@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Dan Carpenter 2017-09-14 02:00:54 +03:00 committed by David S. Miller
parent 6fa9c623a0
commit fa5f7b51fc
1 changed files with 5 additions and 1 deletions
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6
include/net/sctp/ulpevent.h
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@ -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, static inline int sctp_ulpevent_type_enabled(__u16 sn_type,
struct sctp_event_subscribe *mask) struct sctp_event_subscribe *mask)
{ {
int offset = sn_type - SCTP_SN_TYPE_BASE;
char *amask = (char *) mask; 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? */ /* Given an event subscription, is this event enabled? */