CVE-2023-52622: ext4: avoid online resizing failures due to oversized flex bg

CVE-2023-52622: ext4: avoid online resizing failures due to oversized flex bg

[Lee Jones]

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.

The Linux kernel CVE team has assigned CVE-2023-52622 to this issue.


Affected and fixed versions
===========================

	Fixed in 4.19.307 with commit cd1f93ca97a9
	Fixed in 5.4.269 with commit b183fe8702e7
	Fixed in 5.10.210 with commit cfbbb3199e71
	Fixed in 5.15.149 with commit d76c8d7ffe16
	Fixed in 6.1.77 with commit 6d2cbf517dca
	Fixed in 6.6.16 with commit 8b1413dbfe49
	Fixed in 6.7.4 with commit dc3e0f55bec4
	Fixed in 6.8 with commit 5d1935ac02ca

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52622
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ext4/resize.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/cd1f93ca97a9136989f3bd2bf90696732a2ed644
	https://git.kernel.org/stable/c/b183fe8702e78bba3dcef8e7193cab6898abee07
	https://git.kernel.org/stable/c/cfbbb3199e71b63fc26cee0ebff327c47128a1e8
	https://git.kernel.org/stable/c/d76c8d7ffe163c6bf2f1ef680b0539c2b3902b90
	https://git.kernel.org/stable/c/6d2cbf517dcabc093159cf138ad5712c9c7fa954
	https://git.kernel.org/stable/c/8b1413dbfe49646eda2c00c0f1144ee9d3368e0c
	https://git.kernel.org/stable/c/dc3e0f55bec4410f3d74352c4a7c79f518088ee2
	https://git.kernel.org/stable/c/5d1935ac02ca5aee364a449a35e2977ea84509b0