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Subject[73/90] ext4: Fix double-free of blocks with EXT4_IOC_MOVE_EXT
2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
(cherry picked from commit 94d7c16cbbbd0e03841fcf272bcaf0620ad39618)

At the beginning of ext4_move_extent(), we call
ext4_discard_preallocations() to discard inode PAs of orig and donor
inodes. But in the following case, blocks can be double freed, so
move ext4_discard_preallocations() to the end of ext4_move_extents().

1. Discard inode PAs of orig and donor inodes with
ext4_discard_preallocations() in ext4_move_extents().

orig : [ DATA1 ]
donor: [ DATA2 ]

2. While data blocks are exchanging between orig and donor inodes, new
inode PAs is created to orig by other process's block allocation.
(Since there are semaphore gaps in ext4_move_extents().) And new
inode PAs is used partially (2-1).

2-1 Create new inode PAs to orig inode
orig : [ DATA1 | used PA1 | free PA1 ]
donor: [ DATA2 ]

3. Donor inode which has old orig inode's blocks is deleted after
EXT4_IOC_MOVE_EXT finished (3-1, 3-2). So the block bitmap
corresponds to old orig inode's blocks are freed.

3-1 After EXT4_IOC_MOVE_EXT finished
orig : [ DATA2 | free PA1 ]
donor: [ DATA1 | used PA1 ]

3-2 Delete donor inode
orig : [ DATA2 | free PA1 ]
donor: [ FREE SPACE(DATA1) | FREE SPACE(used PA1) ]

4. The double-free of blocks is occurred, when close() is called to
orig inode. Because ext4_discard_preallocations() for orig inode
frees used PA1 and free PA1, though used PA1 is already freed in 3.

4-1 Double-free of blocks is occurred
orig : [ DATA2 | FREE SPACE(free PA1) ]
donor: [ FREE SPACE(DATA1) | DOUBLE FREE(used PA1) ]

Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/move_extent.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -1289,10 +1289,6 @@ ext4_move_extents(struct file *o_filp, s
ext4_ext_get_actual_len(ext_cur), block_end + 1) -
max(le32_to_cpu(ext_cur->ee_block), block_start);

- /* Discard preallocations of two inodes */
- ext4_discard_preallocations(orig_inode);
- ext4_discard_preallocations(donor_inode);
-
while (!last_extent && le32_to_cpu(ext_cur->ee_block) <= block_end) {
seq_blocks += add_blocks;

@@ -1410,6 +1406,11 @@ ext4_move_extents(struct file *o_filp, s

}
out:
+ if (*moved_len) {
+ ext4_discard_preallocations(orig_inode);
+ ext4_discard_preallocations(donor_inode);
+ }
+
if (orig_path) {
ext4_ext_drop_refs(orig_path);
kfree(orig_path);



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