[SRU][M][PATCH 1/1] ext4: fix double-free of blocks due to wrong extents moved_len

[Bethany Jamison]

From: Baokun Li <libaokun1 at huawei.com>

commit 55583e899a5357308274601364741a83e78d6ac4 upstream.

In ext4_move_extents(), moved_len is only updated when all moves are
successfully executed, and only discards orig_inode and donor_inode
preallocations when moved_len is not zero. When the loop fails to exit
after successfully moving some extents, moved_len is not updated and
remains at 0, so it does not discard the preallocations.

If the moved extents overlap with the preallocated extents, the
overlapped extents are freed twice in ext4_mb_release_inode_pa() and
ext4_process_freed_data() (as described in commit 94d7c16cbbbd ("ext4:
Fix double-free of blocks with EXT4_IOC_MOVE_EXT")), and bb_free is
incremented twice. Hence when trim is executed, a zero-division bug is
triggered in mb_update_avg_fragment_size() because bb_free is not zero
and bb_fragments is zero.

Therefore, update move_len after each extent move to avoid the issue.

Reported-by: Wei Chen <harperchen1110 at gmail.com>
Reported-by: xingwei lee <xrivendell7 at gmail.com>
Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@mail.gmail.com
Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base")
CC:  <stable at vger.kernel.org> # 3.18
Signed-off-by: Baokun Li <libaokun1 at huawei.com>
Reviewed-by: Jan Kara <jack at suse.cz>
Link: https://lore.kernel.org/r/20240104142040.2835097-2-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 2883940b19c38d5884c8626483811acf4d7e148f linux.6.6.y)
CVE-2024-26704
Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
---
 fs/ext4/move_extent.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 251584a23d05f..00ba8ca8fd604 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -622,6 +622,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		goto out;
 	o_end = o_start + len;
 
+	*moved_len = 0;
 	while (o_start < o_end) {
 		struct ext4_extent *ex;
 		ext4_lblk_t cur_blk, next_blk;
@@ -676,7 +677,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		 */
 		ext4_double_up_write_data_sem(orig_inode, donor_inode);
 		/* Swap original branches with new branches */
-		move_extent_per_page(o_filp, donor_inode,
+		*moved_len += move_extent_per_page(o_filp, donor_inode,
 				     orig_page_index, donor_page_index,
 				     offset_in_page, cur_len,
 				     unwritten, &ret);
@@ -686,9 +687,6 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		o_start += cur_len;
 		d_start += cur_len;
 	}
-	*moved_len = o_start - orig_blk;
-	if (*moved_len > len)
-		*moved_len = len;
 
 out:
 	if (*moved_len) {
-- 
2.34.1