| Message ID | 20170913092028.idzvduj7ran4li6b@mwanda |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net] sctp: potential read out of bounds in sctp_ulpevent_type_enabled() | expand |
On Wed, Sep 13, 2017 at 12:20:28PM +0300, Dan Carpenter wrote: > 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> > --- > I'm not terribly familiar with sctp and this is a static checker fix. > Please review it carefully. > > diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h > index 1060494ac230..e6873176bea7 100644 > --- a/include/net/sctp/ulpevent.h > +++ b/include/net/sctp/ulpevent.h > @@ -154,7 +154,11 @@ static inline int sctp_ulpevent_type_enabled(__u16 sn_type, > struct sctp_event_subscribe *mask) > { > char *amask = (char *) mask; > - return amask[sn_type - SCTP_SN_TYPE_BASE]; > + int offset = sn_type - SCTP_SN_TYPE_BASE; > + > + if (offset >= sizeof(struct sctp_event_subscribe)) > + return 0; > + return amask[offset]; > } Acked-by: Neil Horman <nhorman@tuxdriver.com> > > /* Given an event subscription, is this event enabled? */ > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
From: Dan Carpenter <dan.carpenter@oracle.com> Date: Wed, 13 Sep 2017 12:20:28 +0300 > @@ -154,7 +154,11 @@ static inline int sctp_ulpevent_type_enabled(__u16 sn_type, > struct sctp_event_subscribe *mask) > { > char *amask = (char *) mask; > - return amask[sn_type - SCTP_SN_TYPE_BASE]; > + int offset = sn_type - SCTP_SN_TYPE_BASE; Please use reverse-christmas-tree local variable ordering. Thank you.
diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h index 1060494ac230..e6873176bea7 100644 --- a/include/net/sctp/ulpevent.h +++ b/include/net/sctp/ulpevent.h @@ -154,7 +154,11 @@ static inline int sctp_ulpevent_type_enabled(__u16 sn_type, struct sctp_event_subscribe *mask) { char *amask = (char *) mask; - return amask[sn_type - SCTP_SN_TYPE_BASE]; + int offset = 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? */
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> --- I'm not terribly familiar with sctp and this is a static checker fix. Please review it carefully.