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authorOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>2013-05-24 15:55:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-05-24 16:22:50 -0700
commit7b92d03c3239f43e5b86c9cc9630f026d36ee995 (patch)
tree230d35077a9c99203a86a7abc94ce8d6645e23fb
parent5eeb929390de7d5219483a1ca10cce4a84066099 (diff)
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fat: fix possible overflow for fat_clusters
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> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/fat/inode.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index dfce656ddb3..5d4513cb1b3 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -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)