linux-kernel - Re: [PATCH] net: sched: Fix memory exposure from short TCA_U32

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Date:   Mon, 27 Aug 2018 10:26:03 -0400
From:   Roman Mashak <mrv@...atatu.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sched: Fix memory exposure from short TCA_U32_SEL

Kees Cook <keescook@...omium.org> writes:

> On Mon, Aug 27, 2018 at 4:46 AM, Jamal Hadi Salim <jhs@...atatu.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@...atatu.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.

While at these changes, could you also add and export in UAPI max
allowed keys count, which is currently 128? For example,
TCA_U32_NKEYS_MAX in pkt_cls.h