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Subject[patch 34/36] ext4: Add sanity check to make_indexed_dir
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: "Theodore Ts'o" <tytso@mit.edu>

(cherry picked from commit e6b8bc09ba2075cd91fbffefcd2778b1a00bd76f)

Make sure the rec_len field in the '..' entry is sane, lest we overrun
the directory block and cause a kernel oops on a purposefully
corrupted filesystem.

Thanks to Sami Liedes for reporting this bug.

http://bugzilla.kernel.org/show_bug.cgi?id=12430

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/namei.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1382,7 +1382,7 @@ static int make_indexed_dir(handle_t *ha
struct fake_dirent *fde;

blocksize = dir->i_sb->s_blocksize;
- dxtrace(printk("Creating index\n"));
+ dxtrace(printk(KERN_DEBUG "Creating index: inode %lu\n", dir->i_ino));
retval = ext4_journal_get_write_access(handle, bh);
if (retval) {
ext4_std_error(dir->i_sb, retval);
@@ -1391,6 +1391,20 @@ static int make_indexed_dir(handle_t *ha
}
root = (struct dx_root *) bh->b_data;

+ /* The 0th block becomes the root, move the dirents out */
+ fde = &root->dotdot;
+ de = (struct ext4_dir_entry_2 *)((char *)fde +
+ ext4_rec_len_from_disk(fde->rec_len));
+ if ((char *) de >= (((char *) root) + blocksize)) {
+ ext4_error(dir->i_sb, __func__,
+ "invalid rec_len for '..' in inode %lu",
+ dir->i_ino);
+ brelse(bh);
+ return -EIO;
+ }
+ len = ((char *) root) + blocksize - (char *) de;
+
+ /* Allocate new block for the 0th block's dirents */
bh2 = ext4_append (handle, dir, &block, &retval);
if (!(bh2)) {
brelse(bh);
@@ -1399,11 +1413,6 @@ static int make_indexed_dir(handle_t *ha
EXT4_I(dir)->i_flags |= EXT4_INDEX_FL;
data1 = bh2->b_data;

- /* The 0th block becomes the root, move the dirents out */
- fde = &root->dotdot;
- de = (struct ext4_dir_entry_2 *)((char *)fde +
- ext4_rec_len_from_disk(fde->rec_len));
- len = ((char *) root) + blocksize - (char *) de;
memcpy (data1, de, len);
de = (struct ext4_dir_entry_2 *) data1;
top = data1 + len;


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