ext4: fix warning in 'ext4_da_release_space'
CVE: CVE-2022-49880
Component: kernel
CWE: CWE-670
Severity: Low
CVSS v3: 2.3/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L
Release date: 2022-01-01T00:00:00+00:00

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix warning in 'ext4_da_release_space'

Syzkaller report issue as follows:
EXT4-fs (loop0): Free/Dirty block details
EXT4-fs (loop0): free_blocks=0
EXT4-fs (loop0): dirty_blocks=0
EXT4-fs (loop0): Block reservation details
EXT4-fs (loop0): i_reserved_data_blocks=0
EXT4-fs warning (device loop0): ext4_da_release_space:1527: ext4_da_release_space: ino 18, to_free 1 with only 0 reserved data blocks
------------[ cut here ]------------
WARNING: CPU: 0 PID: 92 at fs/ext4/inode.c:1528 ext4_da_release_space+0x25e/0x370 fs/ext4/inode.c:1524
Modules linked in:
CPU: 0 PID: 92 Comm: kworker/u4:4 Not tainted 6.0.0-syzkaller-09423-g493ffd6605b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
Workqueue: writeback wb_workfn (flush-7:0)
RIP: 0010:ext4_da_release_space+0x25e/0x370 fs/ext4/inode.c:1528
RSP: 0018:ffffc900015f6c90 EFLAGS: 00010296
RAX: 42215896cd52ea00 RBX: 0000000000000000 RCX: 42215896cd52ea00
RDX: 0000000000000000 RSI: 0000000080000001 RDI: 0000000000000000
RBP: 1ffff1100e907d96 R08: ffffffff816aa79d R09: fffff520002bece5
R10: fffff520002bece5 R11: 1ffff920002bece4 R12: ffff888021fd2000
R13: ffff88807483ecb0 R14: 0000000000000001 R15: ffff88807483e740
FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555569ba628 CR3: 000000000c88e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ext4_es_remove_extent+0x1ab/0x260 fs/ext4/extents_status.c:1461
 mpage_release_unused_pages+0x24d/0xef0 fs/ext4/inode.c:1589
 ext4_writepages+0x12eb/0x3be0 fs/ext4/inode.c:2852
 do_writepages+0x3c3/0x680 mm/page-writeback.c:2469
 __writeback_single_inode+0xd1/0x670 fs/fs-writeback.c:1587
 writeback_sb_inodes+0xb3b/0x18f0 fs/fs-writeback.c:1870
 wb_writeback+0x41f/0x7b0 fs/fs-writeback.c:2044
 wb_do_writeback fs/fs-writeback.c:2187 [inline]
 wb_workfn+0x3cb/0xef0 fs/fs-writeback.c:2227
 process_one_work+0x877/0xdb0 kernel/workqueue.c:2289
 worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
 kthread+0x266/0x300 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
 </TASK>

Above issue may happens as follows:
ext4_da_write_begin
  ext4_create_inline_data
    ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
    ext4_set_inode_flag(inode, EXT4_INODE_INLINE_DATA);
__ext4_ioctl
  ext4_ext_migrate -> will lead to eh->eh_entries not zero, and set extent flag
ext4_da_write_begin
  ext4_da_convert_inline_data_to_extent
    ext4_da_write_inline_data_begin
      ext4_da_map_blocks
        ext4_insert_delayed_block
	  if (!ext4_es_scan_clu(inode, &ext4_es_is_delonly, lblk))
	    if (!ext4_es_scan_clu(inode, &ext4_es_is_mapped, lblk))
	      ext4_clu_mapped(inode, EXT4_B2C(sbi, lblk)); -> will return 1
	       allocated = true;
          ext4_es_insert_delayed_block(inode, lblk, allocated);
ext4_writepages
  mpage_map_and_submit_extent(handle, &mpd, &give_up_on_write); -> return -ENOSPC
  mpage_release_unused_pages(&mpd, give_up_on_write); -> give_up_on_write == 1
    ext4_es_remove_extent
      ext4_da_release_space(inode, reserved);
        if (unlikely(to_free > ei->i_reserved_data_blocks))
	  -> to_free == 1  but ei->i_reserved_data_blocks == 0
	  -> then trigger warning as above

To solve above issue, forbid inode do migrate which has inline data.

Statement: The patch addresses a logical bug in ext4_da_release_space() that could trigger a kernel warning when releasing data blocks for inodes with inline data migrated to extent format. Under rare race or migration scenarios (e.g., syzkaller repro), the function attempted to free a block even though the inode had zero reserved data blocks, producing a WARN and potential state inconsistency.

Remediation: