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fat: fix possible overflow for fat_clusters

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BugLink: http://bugs.launchpad.net/bugs/1191065

commit 7b92d03c32 upstream.

Intermediate value of fat_clusters can be overflowed on 32bits arch.

Reported-by: Krzysztof Strasburger <strasbur@chkw386.ch.pwr.wroc.pl>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ kamal: backport to 3.8 ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Steve Conklin <sconklin@canonical.com>
This commit is contained in:
OGAWA Hirofumi
2013-05-24 15:55:08 -07:00
committed by Steve Conklin
parent 9007538372
commit 8f6d9e64b8
1 changed files with 14 additions and 1 deletions
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15
fs/fat/inode.c
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@@ -1165,6 +1165,19 @@ static int fat_read_root(struct inode *inode)
return 0;
}
static unsigned long calc_fat_clusters(struct super_block *sb)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
/* Divide first to avoid overflow */
if (sbi->fat_bits != 12) {
unsigned long ent_per_sec = sb->s_blocksize * 8 / sbi->fat_bits;
return ent_per_sec * sbi->fat_length;
}
return sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
}
/*
* Read the super block of an MS-DOS FS.
*/
@@ -1363,7 +1376,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;
/* check that FAT table does not overflow */
fat_clusters = sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
fat_clusters = calc_fat_clusters(sb);
total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
if (total_clusters > MAX_FAT(sb)) {
if (!silent)