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

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Date:   Tue, 10 Jan 2017 16:04:06 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     cocci@...teme.lip6.fr, Pengfei Wang <wpengfeinudt@...il.com>,
        Vaishali Thakkar <vthakkar1994@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] coccicheck: add a test for repeat memory fetches

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

-Kees

-- 
Kees Cook
Nexus Security