CVE-2022-49347: kernel: ext4: fix bug_on in ext4_writepages
Component: kernel
Severity: Moderate
CVSS v3: 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Public date: 2025-02-26T00:00:00+00:00

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

ext4: fix bug_on in ext4_writepages

we got issue as follows:
EXT4-fs error (device loop0): ext4_mb_generate_buddy:1141: group 0, block bitmap and bg descriptor inconsistent: 25 vs 31513 free cls
------------[ cut here ]------------
kernel BUG at fs/ext4/inode.c:2708!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 2 PID: 2147 Comm: rep Not tainted 5.18.0-rc2-next-20220413+ #155
RIP: 0010:ext4_writepages+0x1977/0x1c10
RSP: 0018:ffff88811d3e7880 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffff88811c098000
RDX: 0000000000000000 RSI: ffff88811c098000 RDI: 0000000000000002
RBP: ffff888128140f50 R08: ffffffffb1ff6387 R09: 0000000000000000
R10: 0000000000000007 R11: ffffed10250281ea R12: 0000000000000001
R13: 00000000000000a4 R14: ffff88811d3e7bb8 R15: ffff888128141028
FS:  00007f443aed9740(0000) GS:ffff8883aef00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020007200 CR3: 000000011c2a4000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 do_writepages+0x130/0x3a0
 filemap_fdatawrite_wbc+0x83/0xa0
 filemap_flush+0xab/0xe0
 ext4_alloc_da_blocks+0x51/0x120
 __ext4_ioctl+0x1534/0x3210
 __x64_sys_ioctl+0x12c/0x170
 do_syscall_64+0x3b/0x90

It may happen as follows:
1. write inline_data inode
vfs_write
  new_sync_write
    ext4_file_write_iter
      ext4_buffered_write_iter
        generic_perform_write
          ext4_da_write_begin
            ext4_da_write_inline_data_begin -> If inline data size too
            small will allocate block to write, then mapping will has
            dirty page
                ext4_da_convert_inline_data_to_extent ->clear EXT4_STATE_MAY_INLINE_DATA
2. fallocate
do_vfs_ioctl
  ioctl_preallocate
    vfs_fallocate
      ext4_fallocate
        ext4_convert_inline_data
          ext4_convert_inline_data_nolock
            ext4_map_blocks -> fail will goto restore data
            ext4_restore_inline_data
              ext4_create_inline_data
              ext4_write_inline_data
              ext4_set_inode_state -> set inode EXT4_STATE_MAY_INLINE_DATA
3. writepages
__ext4_ioctl
  ext4_alloc_da_blocks
    filemap_flush
      filemap_fdatawrite_wbc
        do_writepages
          ext4_writepages
            if (ext4_has_inline_data(inode))
              BUG_ON(ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))

The root cause of this issue is we destory inline data until call
ext4_writepages under delay allocation mode.  But there maybe already
convert from inline to extent.  To solve this issue, we call
filemap_flush first..


Affected upstream versions: 3.8
Fixed upstream versions: 0, 4.14.283, 4.19.247, 4.9.318, 5.10.121, 5.15.46, 5.17.14, 5.18.3, 5.19, 5.4.198
Upstream repository: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Upstream fix commit: 19918ec7717d87d5ab825884a46b26b21375d7ce