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Subject: Re: [PATCH 5.10 68/77] sctp: add vtag check in sctp_sf_violation
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Xin Long <lucien.xin@gmail.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>, ldv-project@linuxtesting.org
References: <20211101082511.254155853@linuxfoundation.org>
 <20211101082525.833757923@linuxfoundation.org>
 <a3059f52-54c6-6ab3-0f1d-a9b1566ff118@ispras.ru> <YYFevClqyJbASQXH@kroah.com>
 <YYjKd/UwdwrbnrNd@kroah.com>
From:   Alexey Khoroshilov <khoroshilov@ispras.ru>
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Date:   Mon, 8 Nov 2021 10:23:11 +0300
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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

Thank you,
Alexey