linux-kernel - Re: [PATCH] apparmor: initialized returned struct aa

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Message-ID: <CAK8P3a2=SBu6p_xZ61Sv2nnCz2f4Bzv_jpTmGm2F7GGTMkEiow@mail.gmail.com>
Date:   Mon, 20 Nov 2017 17:05:36 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     John Johansen <john.johansen@...onical.com>
Cc:     James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Seth Arnold <seth.arnold@...onical.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] apparmor: initialized returned struct aa_perms

On Mon, Nov 20, 2017 at 4:47 PM, John Johansen
<john.johansen@...onical.com> wrote:
> On 11/20/2017 06:00 AM, Arnd Bergmann wrote:
>> On Mon, Sep 25, 2017 at 4:29 PM, John Johansen
>> <john.johansen@...onical.com> wrote:
>>> On 09/15/2017 03:55 PM, Arnd Bergmann wrote:
>>>> gcc-4.4 points out suspicious code in compute_mnt_perms, where
>>>> the aa_perms structure is only partially initialized before getting
>>>> returned:
>>>>
>>>> security/apparmor/mount.c: In function 'compute_mnt_perms':
>>>> security/apparmor/mount.c:227: error: 'perms.prompt' is used uninitialized in this function
>>>> security/apparmor/mount.c:227: error: 'perms.hide' is used uninitialized in this function
>>>> security/apparmor/mount.c:227: error: 'perms.cond' is used uninitialized in this function
>>>> security/apparmor/mount.c:227: error: 'perms.complain' is used uninitialized in this function
>>>> security/apparmor/mount.c:227: error: 'perms.stop' is used uninitialized in this function
>>>> security/apparmor/mount.c:227: error: 'perms.deny' is used uninitialized in this function
>>>>
>>>> Returning or assigning partially initialized structures is a bit tricky,
>>>> in particular it is explicitly allowed in c99 to assign a partially
>>>> intialized structure to another, as long as only members are read that
>>>> have been initialized earlier. Looking at what various compilers do here,
>>>> the version that produced the warning copied unintialized stack data,
>>>> while newer versions (and also clang) either set the other members to
>>>> zero or don't update the parts of the return buffer that are not modified
>>>> in the temporary structure, but they never warn about this.
>>>>
>>>> In case of apparmor, it seems better to be a little safer and always
>>>> initialize the aa_perms structure. Most users already do that, this
>>>> changes the remaining ones, including the one instance that I got the
>>>> warning for.
>>>>
>>>> Fixes: fa488437d0f9 ("apparmor: add mount mediation")
>>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>>
>>> I've pulled this into apparmor-next
>>
>> It apparently never made it into mainline. What happened?
>>
> Its in apparmor-next and is going with today's pull request

Ok, thanks for checking. I see it in linux-next now, but didn't see
it a linux-next tree from early last week, or in mainline.

      Arnd