From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <jongk@linux-m68k.org>
MIME-Version: 1.0
References: <20180627012421.80B8F24E094@nmr-admin> <1530509350-25410-1-git-send-email-schmitzmic@gmail.com>
In-Reply-To: <1530509350-25410-1-git-send-email-schmitzmic@gmail.com>
From: Kars de Jong <jongk@linux-m68k.org>
Date: Mon, 2 Jul 2018 08:38:55 +0200
Message-ID: <CACz-3rgcLekJq6ou_KCur_KD1Vk7dRGDjXv5oF8C0giMjypFSA@mail.gmail.com>
Subject: Re: [PATCH] block: fix Amiga partition support for disks >= 1 TB
To: schmitzmic@gmail.com
Cc: linux-block@vger.kernel.org, linux-m68k@vger.kernel.org, axboe@kernel.dk,
	geert@linux-m68k.org, jdow@earthlink.net, martin@lichtvoll.de
Content-Type: text/plain; charset="UTF-8"
List-ID: <linux-block@vger.kernel.org>

Op ma 2 jul. 2018 om 07:29 schreef Michael Schmitz <schmitzmic@gmail.com>:
> @@ -98,6 +101,79 @@ int amiga_partition(struct parsed_partitions *state)
>                 if (checksum_block((__be32 *)pb, be32_to_cpu(pb->pb_SummedLongs) & 0x7F) != 0 )
>                         continue;
>
> +               /* RDB gives us more than enough rope to hang ourselves with,
> +                * many times over (2^128 bytes if all fields max out).
> +                * Some careful checks are in order.
> +                */
> +
> +               /* CylBlocks is total number of blocks per cylinder */
> +               cylblk = be32_to_cpu(pb->pb_Environment[3]) *
> +                        be32_to_cpu(pb->pb_Environment[5]);
> +

Could you please create #defines for all these magic offsets in pb_Environment?
Below are a few more.
This makes the code much more readable.
Thanks!

> +               /* check for consistency with RDB defined CylBlocks */
> +               if (cylblk > be32_to_cpu(rdb->rdb_CylBlocks)) {
> +                       pr_err("Dev %s: cylblk 0x%lx > rdb_CylBlocks 0x%x!\n",
> +                               bdevname(state->bdev, b),
> +                               (unsigned long) cylblk,
> +                               be32_to_cpu(rdb->rdb_CylBlocks));
> +               }
> +
> +               /* check for potential overflows - we are going to multiply
> +                * three 32 bit numbers to one 64 bit result later!
> +                * Condition 1: nr_heads * sects_per_track must fit u32!
> +                * NB: This is a HARD limit for AmigaDOS. We don't care much.
> +                */
> +
> +               if (cylblk > UINT_MAX) {
> +                       pr_err("Dev %s: hds*sects 0x%lx > UINT_MAX!\n",
> +                               bdevname(state->bdev, b),
> +                               (unsigned long) cylblk);
> +
> +                       /* lop off low 32 bits */
> +                       cylblk_res = cylblk >> 32;
> +
> +                       /* check for further overflow in end result */
> +                       if (be32_to_cpu(pb->pb_Environment[9]) *
> +                               cylblk_res * blksize > UINT_MAX) {
> +                               pr_err("Dev %s: start_sect overflows u64!\n",
> +                                       bdevname(state->bdev, b));
> +                               res = -1;
> +                               goto rdb_done;
> +                       }
> +
> +                       if (be32_to_cpu(pb->pb_Environment[10]) *
> +                          cylblk_res * blksize > UINT_MAX) {
> +                               pr_err("Dev %s: end_sect overflows u64!\n",
> +                                       bdevname(state->bdev, b));
> +                               res = -1;
> +                               goto rdb_done;
> +                       }
> +               }
> +
> +               /* Condition 2: even if CylBlocks did not overflow, the end
> +                * result must still fit u64!
> +                */
> +
> +               /* how many bits above 32 in cylblk * blksize ? */
> +               if (cylblk*blksize > (u64) UINT_MAX)
> +                       blk_shift = ilog2(cylblk*blksize) - 32;
> +
> +               if (be32_to_cpu(pb->pb_Environment[9])
> +                       > (u64) UINT_MAX>>blk_shift) {
> +                       pr_err("Dev %s: start_sect overflows u64!\n",
> +                               bdevname(state->bdev, b));
> +                       res = -1;
> +                       goto rdb_done;
> +               }
> +
> +               if (be32_to_cpu(pb->pb_Environment[10])
> +                       > (u64) UINT_MAX>>blk_shift) {
> +                       pr_err("Dev %s: end_sect overflows u64!\n",
> +                               bdevname(state->bdev, b));
> +                       res = -1;
> +                       goto rdb_done;
> +               }
> +
>                 /* Tell Kernel about it */
>
>                 nr_sects = (be32_to_cpu(pb->pb_Environment[10]) + 1 -