CVE-2022-49347

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: 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..

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/013f12bdedb96816aaa27ee04349f4433d361f52
• https://git.kernel.org/stable/c/18a759f7f99f0b65a08ff5b7e745fc405a42bde4
• https://git.kernel.org/stable/c/19918ec7717d87d5ab825884a46b26b21375d7ce
• https://git.kernel.org/stable/c/1b061af037646c9cdb0afd8a8d2f1e1c06285866
• https://git.kernel.org/stable/c/1cde35417edc0370fb0179a4e38b78a15350a8d0
• https://git.kernel.org/stable/c/73fd5b19285197078ee8a2e651d75d5b094a4de9
• https://git.kernel.org/stable/c/b2b78f5bf2d453dda3903955efee059260787a42
• https://git.kernel.org/stable/c/de1732b5c1693ad489c5d254f124f67cb775f37d
• https://git.kernel.org/stable/c/ef09ed5d37b84d18562b30cf7253e57062d0db05