linux-kernel - Re: [Cocci] [RFC] coccicheck: add a test for repeat memory fetches

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Date:   Wed, 11 Jan 2017 10:53:53 +0530
From:   Vaishali Thakkar <vaishali.thakkar@...cle.com>
To:     Kees Cook <keescook@...omium.org>,
        Julia Lawall <julia.lawall@...6.fr>
Cc:     Vaishali Thakkar <vthakkar1994@...il.com>,
        Pengfei Wang <wpengfeinudt@...il.com>, cocci@...teme.lip6.fr,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Cocci] [RFC] coccicheck: add a test for repeat memory fetches

On Wednesday 11 January 2017 05:34 AM, Kees Cook wrote:
> On Tue, Jan 10, 2017 at 1:14 PM, Julia Lawall <julia.lawall@...6.fr> wrote:
>> OK, I have the impression that what you are looking for is the following,
>> that currently does not seem to work well. Still maybe it gives an idea.
>>
>> The basic pattern is the following sequence:
>>
>> 1. copy_from_user
>> 2. test on a field of the copied value
>> 3. another copy_from_user
>> 4. a use of the same field as tested in step 2 from the structure obtained
>> by the second copy_from_user or a function call with the structure as an
>> argument
>
> This looks pretty good!
>
>> In the case where the second copy_from_user stores the result in a
>> pointer, then a return with no reference of the tested field is also a
>> concern, unless, the pointer was already kfreed.
>
> I think sequence "2" above missing just looking at a direct value,
> like if instead of a field it was a u32. Also, should binop include
> "=="?
>
> And we need to add back in get_user() too... hmmm

May be having a separate script for get_user would be a good idea. 
get_user needs few more tests than copy_from_user. Also, for the both 
cases we can later add multi-function handling rules. And for the 
get_user, may be combinational usage rule as well.

> -Kees
>