linux-kernel - Re: [PATCH 5.10 68/77] sctp: add vtag check in sctp_sf

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Message-ID: <YYjVHMpu7lfYYHOR@kroah.com>
Date:   Mon, 8 Nov 2021 08:43:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alexey Khoroshilov <khoroshilov@...ras.ru>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Xin Long <lucien.xin@...il.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>, ldv-project@...uxtesting.org
Subject: Re: [PATCH 5.10 68/77] sctp: add vtag check in sctp_sf_violation

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