linux-kernel - Re: [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

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Date:   Mon, 19 Sep 2016 19:52:11 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Colin King <colin.king@...onical.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when
 decrementing index i

On Sat, Sep 17, 2016 at 11:17:50AM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Change predecrement compare to post decrement compare to avoid an
> unsigned integer wrap-around comparisomn when decrementing in the while
> loop.
> 
> For example, if the debugfs_create_file fails when i is zero, the
> current situation will predecrement i in the while loop, wrapping i
> to the maximum signed integer and cause multiple out of bounds reads
> on dfs_fls[i].d as the loop interates to zero.
> 
> Also, as Borislav Petkov suggested, return -ENODEV rather than -ENOMEM
> on the error condition.
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  arch/x86/ras/mce_amd_inj.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
> index cd318d9..20b227f 100644
> --- a/arch/x86/ras/mce_amd_inj.c
> +++ b/arch/x86/ras/mce_amd_inj.c
> @@ -464,13 +464,13 @@ static int __init init_mce_inject(void)
>  	return 0;
>  
>  err_dfs_add:
> -	while (--i >= 0)
> +	while (i-- > 0)

Even better.

Applied,
thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--