netdev - Re: [PATCH net] sctp: hold transport before accessing its asoc in sctp_transport_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CADvbK_f7+UqMqm-ZzEwSz92Joxx_46a1kBrwNbpAi52Qkk=FuQ@mail.gmail.com>
Date:   Wed, 29 Aug 2018 00:08:40 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net] sctp: hold transport before accessing its asoc in sctp_transport_get_next

On Mon, Aug 27, 2018 at 9:08 PM Neil Horman <nhorman@...driver.com> wrote:
>
> On Mon, Aug 27, 2018 at 06:38:31PM +0800, Xin Long wrote:
> > As Marcelo noticed, in sctp_transport_get_next, it is iterating over
> > transports but then also accessing the association directly, without
> > checking any refcnts before that, which can cause an use-after-free
> > Read.
> >
> > So fix it by holding transport before accessing the association. With
> > that, sctp_transport_hold calls can be removed in the later places.
> >
> > Fixes: 626d16f50f39 ("sctp: export some apis or variables for sctp_diag and reuse some for proc")
> > Reported-by: syzbot+fe62a0c9aa6a85c6de16@...kaller.appspotmail.com
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/sctp/proc.c   |  4 ----
> >  net/sctp/socket.c | 22 +++++++++++++++-------
> >  2 files changed, 15 insertions(+), 11 deletions(-)
> >
> > diff --git a/net/sctp/proc.c b/net/sctp/proc.c
> > index ef5c9a8..4d6f1c8 100644
> > --- a/net/sctp/proc.c
> > +++ b/net/sctp/proc.c
> > @@ -264,8 +264,6 @@ static int sctp_assocs_seq_show(struct seq_file *seq, void *v)
> >       }
> >
> >       transport = (struct sctp_transport *)v;
> > -     if (!sctp_transport_hold(transport))
> > -             return 0;
> >       assoc = transport->asoc;
> >       epb = &assoc->base;
> >       sk = epb->sk;
> > @@ -322,8 +320,6 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
> >       }
> >
> >       transport = (struct sctp_transport *)v;
> > -     if (!sctp_transport_hold(transport))
> > -             return 0;
> >       assoc = transport->asoc;
> >
> >       list_for_each_entry_rcu(tsp, &assoc->peer.transport_addr_list,
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index e96b15a..aa76586 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -5005,9 +5005,14 @@ struct sctp_transport *sctp_transport_get_next(struct net *net,
> >                       break;
> >               }
> >
> > +             if (!sctp_transport_hold(t))
> > +                     continue;
> > +
> >               if (net_eq(sock_net(t->asoc->base.sk), net) &&
> >                   t->asoc->peer.primary_path == t)
> >                       break;
> > +
> > +             sctp_transport_put(t);
> >       }
> >
> >       return t;
> > @@ -5017,13 +5022,18 @@ struct sctp_transport *sctp_transport_get_idx(struct net *net,
> >                                             struct rhashtable_iter *iter,
> >                                             int pos)
> >  {
> > -     void *obj = SEQ_START_TOKEN;
> > +     struct sctp_transport *t;
> >
> > -     while (pos && (obj = sctp_transport_get_next(net, iter)) &&
> > -            !IS_ERR(obj))
> > -             pos--;
> > +     if (!pos)
> > +             return SEQ_START_TOKEN;
> >
> > -     return obj;
> > +     while ((t = sctp_transport_get_next(net, iter)) && !IS_ERR(t)) {
> > +             if (!--pos)
> > +                     break;
> > +             sctp_transport_put(t);
> > +     }
> > +
> > +     return t;
> >  }
> >
> >  int sctp_for_each_endpoint(int (*cb)(struct sctp_endpoint *, void *),
> > @@ -5082,8 +5092,6 @@ int sctp_for_each_transport(int (*cb)(struct sctp_transport *, void *),
> >
> >       tsp = sctp_transport_get_idx(net, &hti, *pos + 1);
> >       for (; !IS_ERR_OR_NULL(tsp); tsp = sctp_transport_get_next(net, &hti)) {
> > -             if (!sctp_transport_hold(tsp))
> > -                     continue;
> >               ret = cb(tsp, p);
> >               if (ret)
> >                       break;
> > --
> > 2.1.0
> >
> >
> Acked-by: Neil Horman <nhorman@...driver.com>
>
> Additionally, its not germaine to this particular fix, but why are we still
> using that pos variable in sctp_transport_get_idx?  With the conversion to
> rhashtables, it doesn't seem particularly useful anymore.
For proc, seems so, hti is saved into seq->private.
But for diag, "hti" in sctp_for_each_transport() is a local variable.
do you think where we can save it?