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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxx>
>
> /* Given an event subscription, is this event enabled? */
> --
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