linux-kernel - Re: net/sctp: slab-out-of-bounds in sctp_sf

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Date:   Tue, 25 Oct 2016 10:33:39 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: net/sctp: slab-out-of-bounds in sctp_sf_ootb

On Tue, Oct 25, 2016 at 02:23:48PM +0200, Andrey Konovalov wrote:
> Hi Marcelo,
> 
> I can confirm that your patch fixes the issue for me.
> 
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

Great, thanks Andrey!
I'll post the patch in a few.

> 
> On Mon, Oct 24, 2016 at 9:44 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> > Hi Andrey,
> >
> > On Mon, Oct 24, 2016 at 05:30:04PM +0200, Andrey Konovalov wrote:
> >> The problem is that sctp_walk_errors walks the chunk before its length
> >> is checked for overflow.
> >
> > Exactly. The check is done too late, for the 2nd and subsequent chunks
> > only.
> > Please try the following patch, thanks. Note: not even compile tested.
> >
> > ---8<---
> >
> > diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> > index 026e3bca4a94..8ec20a64a3f8 100644
> > --- a/net/sctp/sm_statefuns.c
> > +++ b/net/sctp/sm_statefuns.c
> > @@ -3422,6 +3422,12 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
> >                         return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
> >                                                   commands);
> >
> > +               /* Report violation if chunk len overflows */
> > +               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
> > +               if (ch_end > skb_tail_pointer(skb))
> > +                       return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
> > +                                                 commands);
> > +
> >                 /* Now that we know we at least have a chunk header,
> >                  * do things that are type appropriate.
> >                  */
> > @@ -3453,12 +3459,6 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
> >                         }
> >                 }
> >
> > -               /* Report violation if chunk len overflows */
> > -               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
> > -               if (ch_end > skb_tail_pointer(skb))
> > -                       return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
> > -                                                 commands);
> > -
> >                 ch = (sctp_chunkhdr_t *) ch_end;
> >         } while (ch_end < skb_tail_pointer(skb));
> >
> --
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