linux-kernel - Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from

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Date:   Mon, 9 Jan 2017 14:02:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     Vaishali Thakkar <vaishali.thakkar@...cle.com>,
        Pengfei Wang <wpengfeinudt@...il.com>,
        Vaishali Thakkar <vthakkar1994@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Marek <mmarek@...e.com>, cocci@...teme.lip6.fr
Subject: Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user

On Mon, Jan 9, 2017 at 12:56 PM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Jan 9, 2017 at 11:08 AM, Julia Lawall <julia.lawall@...6.fr> wrote:
>>
>> On Mon, 9 Jan 2017, Vaishali Thakkar wrote:
>>
>>> Here, may be we should add few more lines from Pengfei's
>>> script to avoid th potential FPs.
>>
>> Which lines (I don't have it handy)?
>
> I'm going to compare
> https://github.com/wpengfei/double_fetch_cocci/blob/master/pattern_match_linux.cocci
> to my original one, add your improvements and see what I get...

Okay, I finally had time to look at this. Pengfei added two other
logical cases that should be checked for, IIUC:

1) destination alias checking (with assignment either before or after
the first copy_from_user):

struct thing object;
struct thing *pointer = &object;

copy_from_user(..., &object);
...
copy_from_user(..., pointer);

2) field writes (via . or ->, instead of short writes):

struct thing object;

copy_from_user(..., &object.field);
...
copy_from_user(..., &object);


It'd probably better to convert Pengfei's into being able to run under
the coccicheck target.

-Kees

-- 
Kees Cook
Nexus Security