On Wed, May 11, 2011 at 02:32:18PM -0400, John Lindgren wrote:
> When looking for a volume label on a FAT32 filesystem, blkid does not
> correctly handle special cluster values in the range 0xFFFFFF8 to
> 0xFFFFFFF, which mark the last cluster in a chain. As a result, it
you mean 0x0FFFFFF8 -- 0x0FFFFFFF, right?
> begins to read [what it treats as] FAT entries from past the end of the
> FAT. Depending on the data read, it may then try to parse random data
> from the filesystem (including user files, free space, and other
> directories) as though it were part of the root directory.
>
> Because parsing stops early when a volume label is found, the problem
> only occurs on filesystems without a volume label. When it occurs, it
> may result in a long sequence of lseek and read calls; on an older IDE
> drive with a 2 GB FAT32 partition, this amounted to around 3 seconds of
> disk I/O.
>
> After patching, blkid stop parsing as soon as it reaches a cluster value
> greater than or equal to the number of entries in the FAT.
>
> Signed-off-by: John Lindgren <john.lindgren@xxxxxxx>
> ---
> shlibs/blkid/src/superblocks/vfat.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/shlibs/blkid/src/superblocks/vfat.c b/shlibs/blkid/src/superblocks/vfat.c
> index 782bc14..39ddcf1 100644
> --- a/shlibs/blkid/src/superblocks/vfat.c
> +++ b/shlibs/blkid/src/superblocks/vfat.c
> @@ -326,9 +326,10 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
> /* Search the FAT32 root dir for the label attribute */
> uint32_t buf_size = vs->vs_cluster_size * sector_size;
> uint32_t start_data_sect = reserved + fat_size;
> + uint32_t entries = vs->vs_fat32_length * sector_size / sizeof(uint32_t);
le32_to_cpu( vs->vs_fat32_length ) * ....
> uint32_t next = le32_to_cpu(vs->vs_root_cluster);
>
> - while (next && --maxloop) {
> + while (next && next < entries && --maxloop) {
> uint32_t next_sect_off;
> uint64_t next_off, fat_entry_off;
> int count;
Fixed & applied, thanks!
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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