linux-kernel - Re: [PATCH] Return error code for failure input for sscanf in parse_cblock

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Message-ID: <5c258e04-10b4-749d-6f15-94a432ab652e@redhat.com>
Date: Mon, 23 Sep 2024 15:26:56 +0200 (CEST)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Dipendra Khadka <kdipendra88@...il.com>
cc: agk@...hat.com, snitzer@...nel.org, dm-devel@...ts.linux.dev, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Return error code for failure input for sscanf in
 parse_cblock_range()

Hi

I skimmed through the sscanf source code and it seems that it can't return 
a negative value at all.

I think, this should be:
	r = sscanf(str, "%llu-%llu%c", &b, &e, &dummy);
	if (r != 2)
		return -EINVAL;

Mikulas

On Sun, 22 Sep 2024, Dipendra Khadka wrote:

> Smatch reported following:
> '''
> drivers/md/dm-cache-target.c:3204 parse_cblock_range() warn: sscanf doesn't return error codes
> drivers/md/dm-cache-target.c:3217 parse_cblock_range() warn: sscanf doesn't return error codes
> '''
> 
> Since, the only negative value that is returned by sscanf is -1.
> Returning -ENVAL when sscanf returns -1.
> 
> Signed-off-by: Dipendra Khadka <kdipendra88@...il.com>
> ---
>  drivers/md/dm-cache-target.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
> index 17f0fab1e254..c35d65e310d6 100644
> --- a/drivers/md/dm-cache-target.c
> +++ b/drivers/md/dm-cache-target.c
> @@ -3200,8 +3200,8 @@ static int parse_cblock_range(struct cache *cache, const char *str,
>  	 * Try and parse form (ii) first.
>  	 */
>  	r = sscanf(str, "%llu-%llu%c", &b, &e, &dummy);
> -	if (r < 0)
> -		return r;
> +	if (r == -1)
> +		return -EINVAL;
>  
>  	if (r == 2) {
>  		result->begin = to_cblock(b);
> @@ -3213,8 +3213,8 @@ static int parse_cblock_range(struct cache *cache, const char *str,
>  	 * That didn't work, try form (i).
>  	 */
>  	r = sscanf(str, "%llu%c", &b, &dummy);
> -	if (r < 0)
> -		return r;
> +	if (r == -1)
> +		return -EINVAL;
>  
>  	if (r == 1) {
>  		result->begin = to_cblock(b);
> -- 
> 2.43.0
>