linux-kernel - Re: [PATCH] hex2bin: fix access beyond string end

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Message-ID: <CAHp75VdHnvv6FH1BKcs8WgGF3nJpj77TsrmsQGBSpsAQU_S-bw@mail.gmail.com>
Date:   Tue, 26 Apr 2022 12:37:08 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Shevchenko <andy@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        device-mapper development <dm-devel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mike Snitzer <msnitzer@...hat.com>,
        Milan Broz <gmazyland@...il.com>
Subject: Re: [PATCH] hex2bin: fix access beyond string end

On Sun, Apr 24, 2022 at 10:48 PM Mikulas Patocka <mpatocka@...hat.com> wrote:
>
> If we pass too short string to "hex2bin" (and the string size without the
> terminating NUL character is even), "hex2bin" reads one byte after the
> terminating NUL character. This patch fixes it.
>
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> Cc: stable@...r.kernel.org

You need to provide a Fixes tag.

...

>         while (count--) {
> -               int hi = hex_to_bin(*src++);
> -               int lo = hex_to_bin(*src++);
> +               int hi, lo;
>
> -               if ((hi < 0) || (lo < 0))
> +               hi = hex_to_bin(*src++);
> +               if (hi < 0)
> +                       return -EINVAL;

return hi;

> +               lo = hex_to_bin(*src++);
> +               if (lo < 0)
>                         return -EINVAL;

return lo;

>                 *dst++ = (hi << 4) | lo;

And on top of that it would be nice to understand if we need to
support half-bytes, but in any case it's not a scope of the patch
right now.

-- 
With Best Regards,
Andy Shevchenko