Re: [PATCH 5.10 68/77] sctp: add vtag check in sctp_sf_violation

Greg Kroah-Hartman
2021-11-08T07:43:30Z

On Mon, Nov 08, 2021 at 10:23:11AM +0300, Alexey Khoroshilov wrote:
> On 08.11.2021 09:57, Greg Kroah-Hartman wrote:
> > On Tue, Nov 02, 2021 at 04:52:28PM +0100, Greg Kroah-Hartman wrote:
> >> On Tue, Nov 02, 2021 at 05:12:16PM +0300, Alexey Khoroshilov wrote:
> >>> Hello!
> >>>
> >>> It seems the patch may lead to NULL pointer dereference.
> >>>
> >>>
> >>> 1. sctp_sf_violation_chunk() calls sctp_sf_violation() with asoc arg
> >>> equal to NULL.
> >>>
> >>> static enum sctp_disposition sctp_sf_violation_chunk(
> >>> ...
> >>> {
> >>> ...
> >>> if (!asoc)
> >>> return sctp_sf_violation(net, ep, asoc, type, arg, commands);
> >>> ...
> >>>
> >>> 2. Newly added code of sctp_sf_violation() calls to sctp_vtag_verify()
> >>> with asoc arg equal to NULL.
> >>>
> >>> enum sctp_disposition sctp_sf_violation(struct net *net,
> >>> ...
> >>> {
> >>> struct sctp_chunk *chunk = arg;
> >>>
> >>> if (!sctp_vtag_verify(chunk, asoc))
> >>> return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
> >>> ...
> >>>
> >>> 3. sctp_vtag_verify() dereferences asoc without any check.
> >>>
> >>> /* Check VTAG of the packet matches the sender's own tag. */
> >>> static inline int
> >>> sctp_vtag_verify(const struct sctp_chunk *chunk,
> >>> const struct sctp_association *asoc)
> >>> {
> >>> /* RFC 2960 Sec 8.5 When receiving an SCTP packet, the endpoint
> >>> * MUST ensure that the value in the Verification Tag field of
> >>> * the received SCTP packet matches its own Tag. If the received
> >>> * Verification Tag value does not match the receiver's own
> >>> * tag value, the receiver shall silently discard the packet...
> >>> */
> >>> if (ntohl(chunk->sctp_hdr->vtag) != asoc->c.my_vtag)
> >>> return 0;
> >>>
> >>>
> >>> Found by Linux Verification Center (linuxtesting.org) with SVACE tool.
> >>
> >> These issues should all be the same with Linus's tree, so can you please
> >> submit patches to the normal netdev developers and mailing list to
> >> resolve the above issues?
> >
> > Given a lack of response, I am going to assume that these are not real
> > issues. If you think they are, please submit patches to the network
> > developers to resolve them.
> >
> > thanks,
> >
> > greg k-h
>
> Hi Greg,
>
> During discussion with the network developers it was defined that the
> code is unreachable and should be removed. The corresponding patch is
> already in network tree:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=e7ea51cd879c

Great, thanks for letting me know.

greg k-h