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Message-ID: <84144f020901050200h3fd6ce71qacd5e2dff282a9@mail.gmail.com>
Date: Mon, 5 Jan 2009 12:00:58 +0200
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
To: "Cyrill Gorcunov" <gorcunov@gmail.com>
Subject: Re: [PATCH] mm: __nr_to_section - make it safe against overflow
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
       "Nick Piggin" <npiggin@suse.de>, "Rik van Riel" <riel@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>, "Jiri Slaby" <jirislaby@gmail.com>
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Hi Cyrill,

On Mon, Jan 5, 2009 at 11:40 AM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> @@ -980,9 +986,12 @@ extern struct mem_section mem_section[NR
>
>  static inline struct mem_section *__nr_to_section(unsigned long nr)
>  {
> -       if (!mem_section[SECTION_NR_TO_ROOT(nr)])
> +       unsigned long idx = SECTION_NR_TO_ROOT(nr);
> +       WARN_ON_ONCE(idx >= NR_SECTION_ROOTS);
> +
> +       if (idx >=NR_SECTION_ROOTS || !mem_section[idx])
>                return NULL;

Looks good to me but I have minor nitpick. You might want to write the
above like this:

    if (WARN_ON_ONCE(idx >= NR_SECTION_ROOTS))
            return NULL;

to separate the error condition from the normal case where we don't
have a mem section.

> -       return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
> +       return &mem_section[idx][nr & SECTION_ROOT_MASK];
>  }