Re: Subject: [PATCH RFC] block: fix Amiga RDB partition support for disks >= 2 TB

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Michael,

Thanks for your patch!

On Wed, Jun 27, 2018 at 4:47 AM <schmitzmic@gmail.com> wrote:
> From 5299e0e64dfb33ac3a1f3137b42178734ce20087 Mon Sep 17 00:00:00 2001

??

> The Amiga RDB partition parser module uses int for partition sector
> address and count, which will overflow for disks 2 TB and larger.
>
> Use sector_t as type for sector address and size (as expected by
> put_partition) to allow using such disks without danger of data
> corruption.

Note that sector_t is not guaranteed to be 64-bit:

    #ifdef CONFIG_LBDAF
    typedef u64 sector_t;
    typedef u64 blkcnt_t;
    #else
    typedef unsigned long sector_t;
    typedef unsigned long blkcnt_t;
    #endif

And it seems CONFIG_LBDAF can still be disabled on 32-bit...

> This bug was reported originally in 2012 by Martin Steigerwald
> <Martin@lichtvoll.de>, and the fix was created by the RDB author,
> Joanne Dow <jdow@earthlink.net>. The patch had been discussed and
> reviewed on linux-m68k at that time but never officially submitted.
>
> Following a stern warning by Joanne, a warning is printed if any
> partition is found to overflow the old 32 bit calculations, on the
> grounds that such a partition would be misparses on legacy 32 bit
> systems (other than Linux).
>
> Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=43511
> Reported-by: Martin Steigerwald <Martin@lichtvoll.de>
> Message-ID: <201206192146.09327.Martin@lichtvoll.de>
> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
> Tested-by: Martin Steigerwald <Martin@lichtvoll.de>
> Tested-by: Michael Schmitz <schmitzmic@gmail.com>
> ---
>  block/partitions/amiga.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/block/partitions/amiga.c b/block/partitions/amiga.c
> index 5609366..42c3f38 100644
> --- a/block/partitions/amiga.c
> +++ b/block/partitions/amiga.c
> @@ -32,7 +32,8 @@ int amiga_partition(struct parsed_partitions *state)
>         unsigned char *data;
>         struct RigidDiskBlock *rdb;
>         struct PartitionBlock *pb;
> -       int start_sect, nr_sects, blk, part, res = 0;
> +       sector_t start_sect, nr_sects;

As sector_t can still be 32-bit, I think you should use an explicit u64 here.

> +       int blk, part, res = 0;
>         int blksize = 1;        /* Multiplier for disk block size */
>         int slot = 1;
>         char b[BDEVNAME_SIZE];
> @@ -111,6 +112,16 @@ int amiga_partition(struct parsed_partitions *state)
>                              be32_to_cpu(pb->pb_Environment[3]) *
>                              be32_to_cpu(pb->pb_Environment[5]) *
>                              blksize;

Without adding any unsigned long long or ULL stuff to the calculations
for start_sect and nr_sects above, the math will still be done using 32-bit
arithmetic. Or am I missing something?

> +               if (start_sect > INT_MAX || nr_sects > INT_MAX
> +                       || (start_sect + nr_sects) > INT_MAX) {
> +                       pr_err("%s: Warning: RDB partition overflow!\n",
> +                               bdevname(state->bdev, b));
> +                       pr_err("%s: start 0x%llX size 0x%llX\n",
> +                               bdevname(state->bdev, b), start_sect,
> +                               nr_sects);
> +                       pr_err("%s: partition incompatible with 32 bit OS\n",
> +                               bdevname(state->bdev, b));
> +               }

I don't know if the check above is really needed here.
There's also int vs. unsigned int. But see below.

>                 put_partition(state,slot++,start_sect,nr_sects);

Given sector_t may be 32-bit, values may be truncated when calling
put_partition(), so you need to check for that.

Interestingly, even partition parsers that do use u64 (efi, ldm) or loff_t
(ibm) do not have such checks.

Perhaps put_partition() should take u64, and print a warning and ignore the
partition if conversion to sector_t involves truncation?

>                 {
>                         /* Be even more informative to aid mounting */

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds