Subject: CVE-2021-47007: f2fs: fix panic during f2fs_resize_fs()

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

f2fs: fix panic during f2fs_resize_fs()

f2fs_resize_fs() hangs in below callstack with testcase:
- mkfs 16GB image & mount image
- dd 8GB fileA
- dd 8GB fileB
- sync
- rm fileA
- sync
- resize filesystem to 8GB

kernel BUG at segment.c:2484!
Call Trace:
 allocate_segment_by_default+0x92/0xf0 [f2fs]
 f2fs_allocate_data_block+0x44b/0x7e0 [f2fs]
 do_write_page+0x5a/0x110 [f2fs]
 f2fs_outplace_write_data+0x55/0x100 [f2fs]
 f2fs_do_write_data_page+0x392/0x850 [f2fs]
 move_data_page+0x233/0x320 [f2fs]
 do_garbage_collect+0x14d9/0x1660 [f2fs]
 free_segment_range+0x1f7/0x310 [f2fs]
 f2fs_resize_fs+0x118/0x330 [f2fs]
 __f2fs_ioctl+0x487/0x3680 [f2fs]
 __x64_sys_ioctl+0x8e/0xd0
 do_syscall_64+0x33/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The root cause is we forgot to check that whether we have enough space
in resized filesystem to store all valid blocks in before-resizing
filesystem, then allocator will run out-of-space during block migration
in free_segment_range().

The Linux kernel CVE team has assigned CVE-2021-47007 to this issue.

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

	Issue introduced in 5.8 with commit b4b10061ef98 and fixed in 5.10.38 with commit 1c20a4896409
	Issue introduced in 5.8 with commit b4b10061ef98 and fixed in 5.11.22 with commit 860afd680d9c
	Issue introduced in 5.8 with commit b4b10061ef98 and fixed in 5.12.5 with commit 822054e5026c
	Issue introduced in 5.8 with commit b4b10061ef98 and fixed in 5.13 with commit 3ab0598e6d86

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-2021-47007
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/f2fs/gc.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/1c20a4896409f5ca1c770e1880c33d0a28a8b10f
	https://git.kernel.org/stable/c/860afd680d9cc1dabd61cda3cd246f60aa1eb705
	https://git.kernel.org/stable/c/822054e5026c43b1dd60cf387dd999e95ee2ecc2
	https://git.kernel.org/stable/c/3ab0598e6d860ef49d029943ba80f627c15c15d6