On Tue, Dec 04, 2018 at 02:39:46PM -0500, Neil Horman wrote:
> On Tue, Dec 04, 2018 at 08:27:41PM +0100, Jakub Audykowicz wrote:
> > If for some reason an association's fragmentation point is zero,
> > sctp_datamsg_from_user will try to endlessly try to divide a message
> > into zero-sized chunks. This eventually causes kernel panic due to
> > running out of memory.
> >
> > Although this situation is quite unlikely, it has occurred before as
> > reported. I propose to add this simple last-ditch sanity check due to
> > the severity of the potential consequences.
> >
> > Signed-off-by: Jakub Audykowicz <jakub.audykowicz@xxxxxxxxx>
> > ---
> > include/net/sctp/sctp.h | 5 +++++
> > net/sctp/chunk.c | 6 ++++++
> > net/sctp/socket.c | 3 +--
> > 3 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> > index ab9242e51d9e..2abbc15824af 100644
> > --- a/include/net/sctp/sctp.h
> > +++ b/include/net/sctp/sctp.h
> > @@ -620,4 +620,9 @@ static inline bool sctp_transport_pmtu_check(struct sctp_transport *t)
> > return false;
> > }
> >
> > +static inline __u32 sctp_min_frag_point(struct sctp_sock *sp, __u16 datasize)
> > +{
> > + return sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT, datasize);
> > +}
> > +
> > #endif /* __net_sctp_h__ */
> > diff --git a/net/sctp/chunk.c b/net/sctp/chunk.c
> > index ce8087846f05..d5b91bc8a377 100644
> > --- a/net/sctp/chunk.c
> > +++ b/net/sctp/chunk.c
> > @@ -191,6 +191,12 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
> > * the packet
> > */
> > max_data = asoc->frag_point;
> > + if (unlikely(!max_data)) {
> > + max_data = sctp_min_frag_point(sctp_sk(asoc->base.sk),
> > + sctp_datachk_len(&asoc->stream));
> > + pr_warn_ratelimited("%s: asoc:%p frag_point is zero, forcing max_data to default minimum (%d)",
> > + __func__, asoc, max_data);
> > + }
> >
> > /* If the the peer requested that we authenticate DATA chunks
> > * we need to account for bundling of the AUTH chunks along with
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index bf618d1b41fd..b8cebd5a87e5 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -3324,8 +3324,7 @@ static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned
> > __u16 datasize = asoc ? sctp_datachk_len(&asoc->stream) :
> > sizeof(struct sctp_data_chunk);
> >
> > - min_len = sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT,
> > - datasize);
> > + min_len = sctp_min_frag_point(sp, datasize);
> > max_len = SCTP_MAX_CHUNK_LEN - datasize;
> >
> > if (val < min_len || val > max_len)
> > --
> > 2.17.1
> >
> >
> Why not just prevent the frag point from ever going below
> SCTP_DEFAULT_MINSEGMENT in the first place in sctp_assoc_update_frag_point?
> Something like:
>
> asoc->frag_point = SCTP_TRUNC4(frag) < SCTP_DEFAILT_MINSEGMENT) ? \
> SCTP_DEFAILT_MINSEGMENT : SCTP_TRUNC4(frag);
>
> Should do the trick I would think
> Neil
This is in the light of "sctp: update frag_point when
stream_interleave is set".
Because of
https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg256575.html
This wouldn't have helped because sctp_assoc_update_frag_point()
didn't get called. The issue is not that the calc issued a bad value,
but that it wasn't done.
Marcelo
