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Date: Wed, 1 Nov 2017 22:26:19 +0100 From: Willy Tarreau <w@....eu> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, linux@...ck-us.net Cc: Dan Carpenter <dan.carpenter@...cle.com>, "David S . Miller" <davem@...emloft.net>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Willy Tarreau <w@....eu> Subject: [PATCH 3.10 078/139] sctp: potential read out of bounds in sctp_ulpevent_type_enabled() From: Dan Carpenter <dan.carpenter@...cle.com> commit fa5f7b51fc3080c2b195fa87c7eca7c05e56f673 upstream. 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@...cle.com> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Signed-off-by: Willy Tarreau <w@....eu> --- include/net/sctp/ulpevent.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h index ca4693b..00c0e5b 100644 --- a/include/net/sctp/ulpevent.h +++ b/include/net/sctp/ulpevent.h @@ -143,8 +143,12 @@ __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? */ -- 2.8.0.rc2.1.gbe9624a
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