On Tue, May 02, 2023 at 10:05:16AM -0700, Kuniyuki Iwashima wrote:
> From: Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>
> Date: Tue, 2 May 2023 13:03:24 +0000
> > The 'sched' index value must be checked before accessing an element
> > of the 'sctp_sched_ops' array. Otherwise, it can lead to buffer overflow.
>
> OOB access ?
My thought as well.
> But it's not true because it does not happen in the first place.
>
> >
> > Note that it's harmless since the 'sched' parameter is checked before
> > calling 'sctp_sched_set_sched'.
> >
> > Found by InfoTeCS on behalf of Linux Verification Center
> > (linuxtesting.org) with SVACE.
> >
> > Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
> > Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
> > Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@xxxxxxxxxxx>
> > ---
> > V2:
> > - Change the order of local variables
> > - Specify the target tree in the subject
> > net/sctp/stream_sched.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/sctp/stream_sched.c b/net/sctp/stream_sched.c
> > index 330067002deb..4d076a9b8592 100644
> > --- a/net/sctp/stream_sched.c
> > +++ b/net/sctp/stream_sched.c
> > @@ -146,18 +146,19 @@ static void sctp_sched_free_sched(struct sctp_stream *stream)
> > int sctp_sched_set_sched(struct sctp_association *asoc,
> > enum sctp_sched_type sched)
> > {
> > - struct sctp_sched_ops *n = sctp_sched_ops[sched];
> > struct sctp_sched_ops *old = asoc->outqueue.sched;
> > struct sctp_datamsg *msg = NULL;
> > + struct sctp_sched_ops *n;
> > struct sctp_chunk *ch;
> > int i, ret = 0;
> >
> > - if (old == n)
> > - return ret;
> > -
> > if (sched > SCTP_SS_MAX)
> > return -EINVAL;
>
> I'd just remove this check instead because the same test is done
> in the caller side, sctp_setsockopt_scheduler(), and this errno
> is never returned.
>
> This unnecessary test confuses a reader like sched could be over
> SCTP_SS_MAX here.
It's actualy better to keep the test here and remove it from the
callers: they don't need to know the specifics, and further new calls
will be protected already.
>
> Since the OOB access does not happen, I think this patch should
> go to net-next without the Fixes tag after the merge window.
Yup.
>
> Thanks,
> Kuniyuki
>
>
> >
> > + n = sctp_sched_ops[sched];
> > + if (old == n)
> > + return ret;
> > +
> > if (old)
> > sctp_sched_free_sched(&asoc->stream);
> >
> > --
> > 2.30.2
