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

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Message-ID: <87139a89-4256-fceb-5ca2-c1077b036eef@redhat.com>
Date: Mon, 23 Sep 2024 17:09:53 +0200 (CEST)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Ming-Hung Tsai <mingnus@...il.com>
cc: Dipendra Khadka <kdipendra88@...il.com>, 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()



On Mon, 23 Sep 2024, Ming-Hung Tsai wrote:

> On Mon, Sep 23, 2024 at 12:47 AM Dipendra Khadka <kdipendra88@...il.com> 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);
> 
> 
> Could you please clarify how to reproduce unexpected results? From
> what I observe, the kernel's sscanf doesn't return -1 on an empty
> input. Even if a negative value other than -EINVAL is returned, it is
> handled by the callers.
> 
> Hank

I applied the patch, but I deleted the conditions "if (r == -1) return 
-EINVAL;"

sscanf in the kernel doesn't return negative numbers.

Mikulas