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From:   Kees Cook <keescook@chromium.org>
Date:   Mon, 27 Aug 2018 07:08:22 -0700
Message-ID: <CAGXu5jJD++hegH4j0ajZNejg8mgcHjqVyjveWj9BFaXwRCV_dQ@mail.gmail.com>
Subject: Re: [PATCH] net: sched: Fix memory exposure from short TCA_U32_SEL
To:     Jamal Hadi Salim <jhs@mojatatu.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        LKML <linux-kernel@vger.kernel.org>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        "David S. Miller" <davem@davemloft.net>,
        Network Development <netdev@vger.kernel.org>
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On Mon, Aug 27, 2018 at 4:46 AM, Jamal Hadi Salim <jhs@mojatatu.com> wrote:
> On 2018-08-26 5:56 p.m., Kees Cook wrote:
>>
>> On Sun, Aug 26, 2018 at 10:30 AM, Jamal Hadi Salim <jhs@mojatatu.com>
>> wrote:
>>>
>>> We should add an nla_policy later.
>>
>>
>> What's the right way to do that for cases like this?
>
>
> Meant something like attached which you alluded-to in your comments
> would give an upper bound (Max allowed keys is 128).

The problem is that policy doesn't parse the contents: "nkeys"
determines the size, so we have to both validate minimum size (to be
sure the location of "nkeys" is valid) and check that the size is at
least nkeys * struct long. I don't think there is a way to do this
with the existing policy language.

-Kees

-- 
Kees Cook
Pixel Security