From 3d4a1c80c4eb97187b3a61b3bfa8c804327f7a45 Mon Sep 17 00:00:00 2001
From: Phillip Lougher <phillip@squashfs.org.uk>
Date: Tue, 3 Jan 2012 02:58:13 +0000
Subject: [PATCH] Squashfs: fix i_blocks calculation with extended regular
 files

The le64_to_cpu() forces the calculation to be unsigned, with
the effect that it can underflow leading to an incorrect large
value.

This bug only triggers in rare(ish) circumstances, an empty file
encoded as an extended regular file or a completely sparse file.
Normally empty files are encoded as a regular file rather than as
an extended regular file (and the regular file i_blocks calculation
doesn't have this bug).  To save space regular file inodes are
optimised to encode the most commonly occurring files.  Less
common regular files are encoded using extended regular file inodes
which contain extra information.

Empty files with nlinks greater than 1, and or empty files
with extended attributes are encoded using extended regular file
inodes and they will hit this bug.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
---
 fs/squashfs/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
index fd7b3b3bda136..81afbccfa8432 100644
--- a/fs/squashfs/inode.c
+++ b/fs/squashfs/inode.c
@@ -208,8 +208,8 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 		inode->i_op = &squashfs_inode_ops;
 		inode->i_fop = &generic_ro_fops;
 		inode->i_mode |= S_IFREG;
-		inode->i_blocks = ((inode->i_size -
-				le64_to_cpu(sqsh_ino->sparse) - 1) >> 9) + 1;
+		inode->i_blocks = (inode->i_size -
+				le64_to_cpu(sqsh_ino->sparse) + 511) >> 9;
 
 		squashfs_i(inode)->fragment_block = frag_blk;
 		squashfs_i(inode)->fragment_size = frag_size;
-- 
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