[U-Boot] [PATCH 1/1] fat: FAT sector offsets overflow on large disks and/or FAT partitions

[Anatolij Gustschin]

Hello,

On Wed, 02 May 2012 19:17:41 -0700
Aaron Williams <Aaron.Williams at cavium.com> wrote:

> This patch fixes several issues where sector offsets can overflow due to
> being limited to 16-bits.  There are many cases which can cause an
> overflow, including large FAT32 partitions and partitions that start at
> a sufficiently large offset on the storage device.

For large FAT32 partitions only changing of fatlength, rootdir_sect and
data_begin is needed to avoid overflows. Changing of fat_sect shouldn't
be needed.

What do you mean exactly by "partitions starting at a sufficiently large
offset on the storage device"? How do you create such partition?
I've tested with a 210 GB FAT32 partition as the fourth primary partition
on a 2 TB disk. This partition is the last partition on the disk, so its
offset is sufficiently large. For this test only fatlength, rootdir_sect
and data_begin was changed to __u32 and int and I do not see issues when
listing or loading the files from this partition.

> Numerous issues were observed and fixed when a 64GB FAT32 filesystem was
> accessed due to truncation.
> 
> Signed-off-by: Aaron Williams <aaron.williams at caviumnetworks.com>
> ---
>  include/fat.h |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/fat.h b/include/fat.h
> index 4c92442..7215628 100644
> --- a/include/fat.h
> +++ b/include/fat.h
> @@ -178,12 +178,12 @@ typedef struct dir_slot {
>  typedef struct {
>         __u8    *fatbuf;        /* Current FAT buffer */
>         int     fatsize;        /* Size of FAT in bits */
> -       __u16   fatlength;      /* Length of FAT in sectors */
> -       __u16   fat_sect;       /* Starting sector of the FAT */
> -       __u16   rootdir_sect;   /* Start sector of root directory */
> -       __u16   sect_size;      /* Size of sectors in bytes */
> +       __u32   fat_sect;       /* Starting sector of the FAT */
> +       __u32   rootdir_sect;   /* Start sector of root directory */
> +       __u32   fatlength;      /* Length of FAT in sectors */
>         __u16   clust_size;     /* Size of clusters in sectors */
> -       short   data_begin;     /* The sector of the first cluster, can be negative */
> +       __u16   sect_size;      /* Size of sectors in bytes */
> +       int     data_begin;     /* The sector of the first cluster, can be negative */
>         int     fatbufnum;      /* Used by get_fatent, init to -1 */
>  } fsdata;

The patch is probably corrupted by your mailer, it doesn't apply.

Thanks,
Anatolij