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References: <20170915195620.1561044-1-arnd@arndb.de> <a94bac78-769a-e8bc-9a98-83a401534935@canonical.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 20 Nov 2017 15:00:37 +0100
Message-ID: <CAK8P3a2SFStvycD4CX+4xtogaoiDXWB0tpeCDKNsYfxD9nDQcw@mail.gmail.com>
Subject: Re: [PATCH] apparmor: initialized returned struct aa_perms
To:     John Johansen <john.johansen@canonical.com>
Cc:     James Morris <james.l.morris@oracle.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Kees Cook <keescook@chromium.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Seth Arnold <seth.arnold@canonical.com>,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        LSM List <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Sep 25, 2017 at 4:29 PM, John Johansen
<john.johansen@canonical.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@arndb.de>
>
> I've pulled this into apparmor-next

It apparently never made it into mainline. What happened?

        Arnd

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