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

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Message-ID: <CAEKBCKMv4-dhWU=a2UnX2rBcQjVTJcF+wg6z6f3qtjA4td-62Q@mail.gmail.com>
Date: Mon, 23 Sep 2024 21:20:33 +0545
From: Dipendra Khadka <kdipendra88@...il.com>
To: Mikulas Patocka <mpatocka@...hat.com>
Cc: Ming-Hung Tsai <mingnus@...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()

Hi,

On Mon, 23 Sept 2024 at 20:55, Mikulas Patocka <mpatocka@...hat.com> wrote:
>
>
>
> 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.
>

Do I have to send v2 with
if (r != 2)
 return -EINVAL;

or what should I do now?
> Mikulas

Best Regards,
Dipendra