Hi,
On Tue, Jun 18, 2019 at 04:04:01PM +0800, Hillf Danton wrote:
>
> Hello Marcelo
>
> On Mon, 17 Jun 2019 22:43:38 +0800 Marcelo Ricardo Leitner wrote:
> > On Mon, Jun 17, 2019 at 10:49:13AM -0300, Marcelo Ricardo Leitner wrote:
> > > Hi,
> > >
> > > On Sun, Jun 16, 2019 at 11:38:03PM +0800, Hillf Danton wrote:
> > > >
> > > > Hello Syzbot
> > > >
> > > > On Sat, 15 Jun 2019 16:36:06 -0700 (PDT) syzbot wrote:
> > > > > Hello,
> > > > >
> > > > > syzbot found the following crash on:
> > > > >
> > > ...
> > > > Check prio_head and bail out if it is not valid.
> > > >
> > > > Thanks
> > > > Hillf
> > > > ----->8---
> > > > ---
> > > > net/sctp/stream_sched_prio.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/net/sctp/stream_sched_prio.c b/net/sctp/stream_sched_prio.c
> > > > index 2245083..db25a43 100644
> > > > --- a/net/sctp/stream_sched_prio.c
> > > > +++ b/net/sctp/stream_sched_prio.c
> > > > @@ -135,6 +135,8 @@ static void sctp_sched_prio_sched(struct sctp_stream *stream,
> > > > struct sctp_stream_priorities *prio, *prio_head;
> > > >
> > > > prio_head = soute->prio_head;
> > > > + if (!prio_head)
> > > > + return;
> > > >
> > > > /* Nothing to do if already scheduled */
> > > > if (!list_empty(&soute->prio_list))
> > > > --
> > >
> > > Thanks but this is not a good fix for this. It will cause the stream
> > > to never be scheduled.
> > >
> Thanks very much for the light you are casting.
>
> > > The problem happens because of the fault injection that happened a bit
> > > before the crash, in here:
> > >
> > > int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)
> > > {
> > > struct sctp_stream_out_ext *soute;
> > >
> > > soute = kzalloc(sizeof(*soute), GFP_KERNEL);
> > > if (!soute)
> > > return -ENOMEM;
> > > SCTP_SO(stream, sid)->ext = soute; <---- [A]
> > >
> > > return sctp_sched_init_sid(stream, sid, GFP_KERNEL);
> > > ^^^^^^^^^^^^---- [B] failed
> > > }
> > >
> Eagle eye.
>
> > > This causes the 1st sendmsg to bail out with the error. When the 2nd
> > > one gets in, it will:
> > >
> > > sctp_sendmsg_to_asoc()
> > > {
> > > ...
> > > if (unlikely(!SCTP_SO(&asoc->stream, sinfo->sinfo_stream)->ext)) {
> > > ^^^^^--- [C]
> > > err = sctp_stream_init_ext(&asoc->stream, sinfo->sinfo_stream);
> > > if (err)
> > > goto err;
> > > }
> > >
> > > [A] leaves ext initialized, despite the failed in [B]. Then in [C], it
> > > will not try to initialize again.
> > >
> Fairly concise.
>
> > > We need to either uninitialize ->ext as error handling for [B], or
> > > improve the check on [C].
> >
> > The former one, please. This should be enough (untested):
> >
> > diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> > index 93ed07877337..25946604af85 100644
> > --- a/net/sctp/stream.c
> > +++ b/net/sctp/stream.c
> > @@ -153,13 +153,20 @@ int sctp_stream_init(struct sctp_stream *stream, __u1=
> > 6 outcnt, __u16 incnt,
> > int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)
> > {
> > struct sctp_stream_out_ext *soute;
> > + int ret;
> >
> > soute = kzalloc(sizeof(*soute), GFP_KERNEL);
> > if (!soute)
> > return -ENOMEM;
> > SCTP_SO(stream, sid)->ext = soute;
> >
> > - return sctp_sched_init_sid(stream, sid, GFP_KERNEL);
> > + ret = sctp_sched_init_sid(stream, sid, GFP_KERNEL);
> > + if (ret) {
> > + kfree(SCTP_SO(stream, sid)->ext);
> > + SCTP_SO(stream, sid)->ext = NULL;
[D]
> > + }
> > +
> > + return ret;
> > }
> >
> Definitely nice.
>
> > void sctp_stream_free(struct sctp_stream *stream)
> >
> Hmmm, ->ext will be valid, provided it is loaded with a valid slab in
> sctp_stream_init_ext() regardless of whether sid is successfully
> initialised, until it is released, for instance, in sctp_stream_free(),
> and based on that assumption, it looks hardly likely that ->ext has a
> chance to create a gfp in sctp_sched_prio_sched().
I'm not sure I follow you. Anyway, with the patch above, after calling
sctp_stream_init_ext() ->ext will be either completely valid, or it
will not be present at all as it is seting ->ext to NULL if sid
initialization ended up failing.
Marcelo
