linux-kernel - Re: [PATCH 1/2] ext4: fix warning about stack corruption

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Message-ID: <CAK8P3a05GOh87tGhnuUS_gYmQVjgTrC-e58KagVPG4hHSuFTgg@mail.gmail.com>
Date:   Tue, 22 Aug 2017 13:57:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Anton Blanchard <anton@...abs.org>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        linux-ext4@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ext4: fix warning about stack corruption

On Tue, Aug 22, 2017 at 1:08 PM, Anton Blanchard <anton@...abs.org> wrote:
> Hi Arnd,
>>
>> Note that while clang won't allow certain kinds of variable-length
>> arrays in structures, this particular instance is fine, as the array
>> is at the end of the structure, and the size is strictly bounded.
>
> Unfortunately it doesn't appear to work, at least with ppc64le clang:
>
> fs/ext4/mballoc.c:2303:17: error: fields must have a constant size: 'variable length array in structure' extension will never be supported
>         ext4_grpblk_t counters[blocksize_bits + 2];

My fix for this is in the ext4/dev branch in linux-next, I hope it still
makes it into v4.13.

       Arnd