[017/141] fat: fix possible overflow for fat_clusters

Steven Rostedt
2013-07-03T18:55:22Z

[-- Attachment #1: 0017-fat-fix-possible-overflow-for-fat_clusters.patch --]
[-- Type: text/plain, Size: 1786 bytes --]

3.6.11.6 stable review patch.
If anyone has any objections, please let me know.

------------------

From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

[ Upstream commit 7b92d03c3239f43e5b86c9cc9630f026d36ee995 ]

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>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
fs/fat/inode.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 05e897f..ca5241f 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1212,6 +1212,19 @@ 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.
*/
@@ -1409,7 +1422,7 @@ 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)
--
1.7.10.4