linux-kernel - Re: [PATCH] lib/bitmap.c: return -EINVAL for grouping errors in __bitmap

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Date:	Mon, 29 Jun 2015 16:39:01 +0300
From:	Yury Norov <yury.norov@...il.com>
To:	Pan Xinhui <xinhuix.pan@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>, tj@...nel.org,
	peterz@...radead.org, sudeep.holla@....com, mina86@...a86.com,
	"mnipxh@....com" <mnipxh@....com>,
	Alexey Klimov <klimov.linux@...il.com>
Subject: Re: [PATCH] lib/bitmap.c: return -EINVAL for grouping errors in __bitmap_parselist

> Sometimes the input from user may cause an unexpected result.

Could you please provide specific example?

>
> just like __bitmap_parse, we return -EINVAL if there is no avaiable digit in each
> parsing procedures.
>
> Signed-off-by: Pan Xinhui <xinhuix.pan@...el.com>

Hello, Pan.

(Adding Alexey Klimov, Rasmus Villemoes)

> ---
>   lib/bitmap.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 64c0926..995fca2 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -504,7 +504,7 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>           int nmaskbits)
>   {
>       unsigned a, b;
> -    int c, old_c, totaldigits;
> +    int c, old_c, totaldigits, ndigits;
>       const char __user __force *ubuf = (const char __user __force *)buf;
>       int exp_digit, in_range;
>
> @@ -514,6 +514,7 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>           exp_digit = 1;
>           in_range = 0;
>           a = b = 0;
> +        ndigits = 0;
>
>           /* Get the next cpu# or a range of cpu#'s */
>           while (buflen) {
> @@ -555,8 +556,10 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>               if (!in_range)
>                   a = b;
>               exp_digit = 0;
> -            totaldigits++;
> +            ndigits++; totaldigits++;

I'm not happy with joining two statements to a single line.
Maybe sometimes it's OK for loop iterators like

    while (a[i][j]) {
        i++; j++;
    }

But here it looks nasty. Anyway, it's minor.

>           }
> +        if (ndigits == 0)
> +            return -EINVAL;

You can avoid in-loop incrementation of ndigits if you'll
save current totaldigits to ndigits before loop, and check
ndigits against totaldigits after the loop:

    ndigits = totaldigits;
    while (...) {
         ...
        totaldigits++;
    }

    if (ndigits == totaldigits)
        return -EINVAL;

Maybe it's a good point to rework initial __bitmap_parse() similar way...

>           if (!(a <= b))
>               return -EINVAL;
>           if (b >= nmaskbits)
> --
> 1.9.1
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