Re: [PATCH v5 1/2] block: fix signed int overflow in Amiga partition support

[Michael Schmitz <schmitzmic@xxxxxxxxx>]

Hi Geert,

Am 12.10.2018 um 21:59 schrieb Geert Uytterhoeven:

> > Changes from v4:
> >
> > Andreas Schwab:
> > - correct cast to sector_t in sector address calculations
>
> Which you only did for the first case...
>
> > --- a/block/partitions/amiga.c
> > +++ b/block/partitions/amiga.c
>
> > @@ -100,14 +101,14 @@ int amiga_partition(struct parsed_partitions *state)
> >
> >                 /* Tell Kernel about it */
> >
> > -               nr_sects = (be32_to_cpu(pb->pb_Environment[10]) + 1 -
> > -                           be32_to_cpu(pb->pb_Environment[9])) *
> > +               nr_sects = ((sector_t) be32_to_cpu(pb->pb_Environment[10])
>
> ...here ...
>
> > +                          + 1 - be32_to_cpu(pb->pb_Environment[9])) *
> >                            be32_to_cpu(pb->pb_Environment[3]) *
> >                            be32_to_cpu(pb->pb_Environment[5]) *
> >                            blksize;
> >                 if (!nr_sects)
> >                         continue;
> > -               start_sect = be32_to_cpu(pb->pb_Environment[9]) *
> > +               start_sect = (sector_t) be32_to_cpu(pb->pb_Environment[9]) *
>
> ... but not here?

I meant to cast the first operand to sector_t here?

Using

int main(int argc, char *argv) {
  unsigned int a, b;
  unsigned long long c, d;

  a = 0xffffffff;
  b = 0xffffffff;

  c = a * b;
  d = (unsigned long long) a * b;

  fprintf(stdout, "%llx %llx\n", c, d);
}

I get this:

1 fffffffe00000001

But I can add brackets if you think the compiler might get this wrong.

Cheers,

	Michael

> >                              be32_to_cpu(pb->pb_Environment[3]) *
> >                              be32_to_cpu(pb->pb_Environment[5]) *
> >                              blksize;
>
> Gr{oetje,eeting}s,
>
>                         Geert