netdev - Re: [Patch net] net_sched: add max len check for TCA

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Message-ID: <CAM_iQpUomr7PkWahew9WkhNnKB7QGg0gTjurccLEwkgh24TARw@mail.gmail.com>
Date:   Fri, 4 Oct 2019 16:23:40 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        David Ahern <dsahern@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        syzbot <syzbot+618aacd49e8c8b8486bd@...kaller.appspotmail.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net] net_sched: add max len check for TCA_KIND

On Fri, Oct 4, 2019 at 3:54 PM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Thu, 3 Oct 2019 16:45:25 -0300, Marcelo Ricardo Leitner wrote:
> > On Sat, Sep 21, 2019 at 07:24:34PM -0700, Jakub Kicinski wrote:
> > > Applied, queued for 4.14+, thanks!
> >
> > Ahm, this breaks some user applications.
> >
> > I'm getting "Attribute failed policy validation" extack error while
> > adding ingress qdisc on an app using libmnl, because it just doesn't
> > pack the null byte there if it uses mnl_attr_put_str():
> > https://git.netfilter.org/libmnl/tree/src/attr.c#n481
> > Unless it uses mnl_attr_put_strz() instead.
> >
> > Though not sure who's to blame here, as one could argue that the
> > app should have been using the latter in the first place, but well..
> > it worked and produced the right results.
> >
> > Ditto for 199ce850ce11 ("net_sched: add policy validation for action
> > attributes") on TCA_ACT_KIND.
>
> Thanks for the report Marcelo! This netlink validation stuff is always
> super risky I figured better find out if something breaks sooner than
> later, hence the backport.
>
> So if I'm understanding this would be the fix?

Of course not, you just break KMSAN again. Please read the original
report.

I will send a patch to use nla_strlcpy() instead, I think it will make
everyone happy here.

Thanks.