Re: [PATCH v1] vdpa: Complement vdpa_nl_policy for nlattr length check

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Lin Ma <linma@zju.edu.cn>
Cc: xuanzhuo@linux.alibaba.com, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v1] vdpa: Complement vdpa_nl_policy for nlattr length check
Date: Sun, 23 Jul 2023 05:55:33 -0400	[thread overview]
Message-ID: <20230723053613-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <729f5c17.e4079.18982192866.Coremail.linma@zju.edu.cn>

On Sun, Jul 23, 2023 at 05:33:54PM +0800, Lin Ma wrote:
> Hello Michael,
> 
> > >
> > > The vdpa_nl_policy structure is used to validate the nlattr when parsing
> > > the incoming nlmsg. It will ensure the attribute being described produces
> > > a valid nlattr pointer in info->attrs before entering into each handler
> > > in vdpa_nl_ops.
> > > 
> > > That is to say, the missing part in vdpa_nl_policy may lead to illegal
> > > nlattr after parsing, which could lead to OOB read just like CVE-2023-3773.
> > 
> > Hmm.
> > 
> > https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-3773
> > 
> > ** RESERVED ** This candidate has been reserved by an organization or individual that will use it when announcing a new security problem. When the candidate has been publicized, the details for this candidate will be provided.
> > 
> 
> Yeah, that CVE is assigned while fix not upstream yet. FYI, the fix is pending too. 
> See, https://marc.info/?l=linux-kernel&m=169009801131058&w=2.
> 
> > 
> > > This patch adds three missing nla_policy to avoid such bugs.
> > > 
> > > Fixes: 90fea5a800c3 ("vdpa: device feature provisioning")
> > > Fixes: 13b00b135665 ("vdpa: Add support for querying vendor statistics")
> > > Fixes: ad69dd0bf26b ("vdpa: Introduce query of device config layout")
> > > Signed-off-by: Lin Ma <linma@zju.edu.cn>
> > 
> > I don't know how OOB triggers but this duplication is problematic I
> > think: we are likely to forget again in the future.  Isn't there a way
> > to block everything that is not listed?
> > 
> 
> Sure, that is another undergoing task I'm working on. If the nlattr is parsed with
> NL_VALIDATE_UNSPEC, any forgotten nlattr will be rejected, therefore (which is the default
> for modern nla_parse). The problem here is that there are still consumers for
> nla_parse_deprecated. And we cannot simply replace all *_deprecated to modern ones
> as it may break userspace. See the commit message in 8cb081746c03 ("netlink: make
> validation more configurable for future strictness")
> 
> I believe if we can do enough test against userspace toolchains, we can ultimately
> upgrade all *_depprecated parsers to modern ones, which costs time and efforts. This
> send patch is a much simpler (but temporary) solution for now.
> 
> Regards
> Lin

Hmm but vdpa does not use nla_parse_deprecated does it? And in fact was
introduced after 8cb081746c031fb164089322e2336a0bf5b3070c.
So why is there an issue in vdpa?

-- 
MST

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