Re: [PATCH] Return error code for failure input for sscanf in parse_cblock_range()

[Mikulas Patocka <mpatocka@redhat.com>]

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On Mon, 23 Sep 2024, Dipendra Khadka wrote:

> Hi,
> 
> On Mon, 23 Sept 2024 at 20:55, Mikulas Patocka <mpatocka@redhat.com> wrote:
> >
> >
> >
> > On Mon, 23 Sep 2024, Ming-Hung Tsai wrote:
> >
> > > On Mon, Sep 23, 2024 at 12:47 AM Dipendra Khadka <kdipendra88@gmail.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@gmail.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

You can do nothing :)

I fixed the patch and I'll send it to Linus in this merge window.

Mikulas