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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>
This commit is contained in:
Phillip Lougher 2012-01-03 02:58:13 +00:00
parent cc37f75a9f
commit 3d4a1c80c4
1 changed files with 2 additions and 2 deletions
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4
fs/squashfs/inode.c
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@ -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;