Patch "fat: fix possible overflow for fat_clusters" has been added to the 3.4-stable tree

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This is a note to let you know that I've just added the patch titled

    fat: fix possible overflow for fat_clusters

to the 3.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fat-fix-possible-overflow-for-fat_clusters.patch
and it can be found in the queue-3.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 7b92d03c3239f43e5b86c9cc9630f026d36ee995 Mon Sep 17 00:00:00 2001
From: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Date: Fri, 24 May 2013 15:55:08 -0700
Subject: fat: fix possible overflow for fat_clusters

From: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>

commit 7b92d03c3239f43e5b86c9cc9630f026d36ee995 upstream.

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

Reported-by: Krzysztof Strasburger <strasbur@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/fat/inode.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1237,6 +1237,19 @@ 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.
  */
@@ -1433,7 +1446,7 @@ int fat_fill_super(struct super_block *s
 		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)


Patches currently in stable-queue which might be from hirofumi@xxxxxxxxxxxxxxxxxx are

queue-3.4/fat-fix-possible-overflow-for-fat_clusters.patch
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