From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Subject: [PATCH net] sctp: potential read out of bounds in sctp_ulpevent_type_enabled() Date: Wed, 13 Sep 2017 12:20:28 +0300 Message-ID: <20170913092028.idzvduj7ran4li6b@mwanda> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Neil Horman , "David S. Miller" , linux-sctp@vger.kernel.org, netdev@vger.kernel.org, kernel-janitors@vger.kernel.org To: Vlad Yasevich Return-path: Content-Disposition: inline Sender: kernel-janitors-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 --- 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]; } /* Given an event subscription, is this event enabled? */