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

[Lin Ma]

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@xxxxxxxxxx>
> 
> 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