linux-kernel - Re: [PATCH 5/7] lib: rework bitmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Mon, 9 Sep 2019 13:06:08 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Tobin C . Harding" <tobin@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Vineet Gupta <vineet.gupta1@...opsys.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH 5/7] lib: rework bitmap_parse()

On Sun, Sep 08, 2019 at 08:30:19PM -0700, Yury Norov wrote:
> bitmap_parse() is ineffective and full of opaque variables and opencoded
> parts. It leads to hard understanding and usage of it. This rework
> includes:
>  - remove bitmap_shift_left() call from the cycle. Now it makes the
>    complexity of the algorithm as O(nbits^2). In the suggested approach
>    the input string is parsed in reverse direction, so no shifts needed;
>  - relax requirement on a single comma and no white spaces between chunks.
>    It is considered useful in scripting, and it aligns with
>    bitmap_parselist();
>  - split bitmap_parse() to small readable helpers;
>  - make an explicit calculation of the end of input line at the
>    beginning, so users of the bitmap_parse() won't bother doing this.

> +static const char *bitmap_get_x32_reverse(const char *start,
> +					const char *end, u32 *num)
> +{
> +	u32 ret = 0;
> +	int c, i;
> +

> +	if (!isxdigit(*end))
> +		return ERR_PTR(-EINVAL);

This seems redundant...

> +
> +	for (i = 0; i < 32; i += 4) {

> +		c = hex_to_bin(*end--);
> +		if (c < 0)
> +			return ERR_PTR(-EINVAL);

...because this will do the same check.

Am I right?

> +
> +		ret |= c << i;
> +
> +		if (start > end || __end_of_region(*end))
> +			goto out;
> +	}
> +

> +	if (isxdigit(*end))
> +		return ERR_PTR(-EOVERFLOW);

hex_to_bin() doesn't rely on ctype array, won't drain caches.
I guess it's not a fast path, so, either will work.

> +out:
> +	*num = ret;
> +	return end;
> +}

-- 
With Best Regards,
Andy Shevchenko