From: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Subject: fat: fix possible overflow for fat_clusters
Intermediate value of fat_clusters can be overflowed on 32bits arch.
Reported-by: Krzysztof Strasburger <strasbur@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fat/inode.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff -puN fs/fat/inode.c~fat-fix-possible-overflow-for-fat_clusters fs/fat/inode.c
--- a/fs/fat/inode.c~fat-fix-possible-overflow-for-fat_clusters
+++ a/fs/fat/inode.c
@@ -1229,6 +1229,19 @@ static int fat_read_root(struct inode *i
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 *s
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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