Commit 7b92d03c authored by OGAWA Hirofumi's avatar OGAWA Hirofumi Committed by Linus Torvalds

fat: fix possible overflow for fat_clusters

Intermediate value of fat_clusters can be overflowed on 32bits arch.
Reported-by: 's avatarKrzysztof Strasburger <strasbur@chkw386.ch.pwr.wroc.pl>
Signed-off-by: 's avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5eeb9293
......@@ -1229,6 +1229,19 @@ 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.
*/
......@@ -1434,7 +1447,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
sbi->dirty = b->fat16.state & FAT_STATE_DIRTY;
/* 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)
......
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