title: ext4: avoid online resizing failures due to oversized flex bg
description: In the Linux kernel, the following vulnerability has been resolved:
ext4: avoid online resizing failures due to oversized flex bg
When we online resize an ext4 filesystem with a oversized flexbg_size,
mkfs.ext4 -F -G 67108864 $dev -b 4096 100M
mount $dev $dir
resize2fs $dev 16G
the following WARN_ON is triggered:
==================================================================
WARNING: CPU: 0 PID: 427 at mm/page_alloc.c:4402 __alloc_pages+0x411/0x550
Modules linked in: sg(E)
CPU: 0 PID: 427 Comm: resize2fs Tainted: G  E  6.6.0-rc5+ #314
RIP: 0010:__alloc_pages+0x411/0x550
Call Trace:
<TASK>
__kmalloc_large_node+0xa2/0x200
__kmalloc+0x16e/0x290
ext4_resize_fs+0x481/0xd80
__ext4_ioctl+0x1616/0x1d90
ext4_ioctl+0x12/0x20
__x64_sys_ioctl+0xf0/0x150
do_syscall_64+0x3b/0x90
==================================================================
This is because flexbg_size is too large and the size of the new_group_data
array to be allocated exceeds MAX_ORDER. Currently, the minimum value of
MAX_ORDER is 8, the minimum value of PAGE_SIZE is 4096, the corresponding
maximum number of groups that can be allocated is:
(PAGE_SIZE << MAX_ORDER) / sizeof(struct ext4_new_group_data) ≈ 21845
And the value that is down-aligned to the power of 2 is 16384. Therefore,
this value is defined as MAX_RESIZE_BG, and the number of groups added
each time does not exceed this value during resizing, and is added multiple
times to complete the online resizing. The difference is that the metadata
in a flex_bg may be more dispersed.
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 1da177e4c3f4, lessThan: cd1f93ca97a9, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: b183fe8702e7, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: cfbbb3199e71, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: d76c8d7ffe16, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: 6d2cbf517dca, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: 8b1413dbfe49, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: dc3e0f55bec4, status: affected, versionType: git
version: 1da177e4c3f4, lessThan: 5d1935ac02ca, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 4.19.307, lessThanOrEqual: 4.19.*, status: unaffected, versionType: custom
version: 5.4.269, lessThanOrEqual: 5.4.*, status: unaffected, versionType: custom
version: 5.10.210, lessThanOrEqual: 5.10.*, status: unaffected, versionType: custom
version: 5.15.149, lessThanOrEqual: 5.15.*, status: unaffected, versionType: custom
version: 6.1.77, lessThanOrEqual: 6.1.*, status: unaffected, versionType: custom
version: 6.6.16, lessThanOrEqual: 6.6.*, status: unaffected, versionType: custom
version: 6.7.4, lessThanOrEqual: 6.7.*, status: unaffected, versionType: custom
version: 6.8, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
