From a2bddbb69ccbc732605df19c99dc6411ee359ba5 Mon Sep 17 00:00:00 2001 From: Anmol Jain Date: Wed, 16 Jul 2025 21:47:46 +0000 Subject: [PATCH] ext4: fix double-free of blocks due to wrong extents moved_len jira VULN-4776 cve CVE-2024-26704 commit-author Baokun Li commit 55583e899a5357308274601364741a83e78d6ac4 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 Reported-by: xingwei lee Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@mail.gmail.com Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base") CC: # 3.18 Signed-off-by: Baokun Li Reviewed-by: Jan Kara Link: https://lore.kernel.org/r/20240104142040.2835097-2-libaokun1@huawei.com Signed-off-by: Theodore Ts'o (cherry picked from commit 55583e899a5357308274601364741a83e78d6ac4) Signed-off-by: Anmol Jain --- 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 b8e2d3ffee0a8..579d029de92d0 100644 --- a/fs/ext4/move_extent.c +++ b/fs/ext4/move_extent.c @@ -615,6 +615,7 @@ 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; @@ -670,7 +671,7 @@ 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); @@ -680,9 +681,6 @@ 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) {