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SubjectRe: general protection fault in sctp_sched_prio_sched
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.
>
> 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
> }
>
> 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.
>
> 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, __u16 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;
+ }
+
+ return ret;
}

void sctp_stream_free(struct sctp_stream *stream)
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