linux-kernel - [82/85] ext4: fix overflow when counting used blocks on 32-bit architectures

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Message-ID: <lsq.1374674565.79166003@decadent.org.uk>
Date:	Wed, 24 Jul 2013 15:02:45 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jan Kara" <jack@...e.cz>,
	"Theodore Ts'o" <tytso@....edu>
Subject: [82/85] ext4: fix overflow when counting used blocks on 32-bit
 architectures

3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jan Kara <jack@...e.cz>

commit 8af8eecc1331dbf5e8c662022272cf667e213da5 upstream.

The arithmetics adding delalloc blocks to the number of used blocks in
ext4_getattr() can easily overflow on 32-bit archs as we first multiply
number of blocks by blocksize and then divide back by 512. Make the
arithmetics more clever and also use proper type (unsigned long long
instead of unsigned long).

Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4335,7 +4335,7 @@ int ext4_getattr(struct vfsmount *mnt, s
 		 struct kstat *stat)
 {
 	struct inode *inode;
-	unsigned long delalloc_blocks;
+	unsigned long long delalloc_blocks;
 
 	inode = dentry->d_inode;
 	generic_fillattr(inode, stat);
@@ -4352,7 +4352,7 @@ int ext4_getattr(struct vfsmount *mnt, s
 	 */
 	delalloc_blocks = EXT4_I(inode)->i_reserved_data_blocks;
 
-	stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
+	stat->blocks += delalloc_blocks << (inode->i_sb->s_blocksize_bits-9);
 	return 0;
 }
 

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