Subject: CVE-2024-44941: f2fs: fix to cover read extent cache access with lock

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

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

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

f2fs: fix to cover read extent cache access with lock

syzbot reports a f2fs bug as below:

BUG: KASAN: slab-use-after-free in sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
Read of size 4 at addr ffff8880739ab220 by task syz-executor200/5097

CPU: 0 PID: 5097 Comm: syz-executor200 Not tainted 6.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
 do_read_inode fs/f2fs/inode.c:509 [inline]
 f2fs_iget+0x33e1/0x46e0 fs/f2fs/inode.c:560
 f2fs_nfs_get_inode+0x74/0x100 fs/f2fs/super.c:3237
 generic_fh_to_dentry+0x9f/0xf0 fs/libfs.c:1413
 exportfs_decode_fh_raw+0x152/0x5f0 fs/exportfs/expfs.c:444
 exportfs_decode_fh+0x3c/0x80 fs/exportfs/expfs.c:584
 do_handle_to_path fs/fhandle.c:155 [inline]
 handle_to_path fs/fhandle.c:210 [inline]
 do_handle_open+0x495/0x650 fs/fhandle.c:226
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

We missed to cover sanity_check_extent_cache() w/ extent cache lock,
so, below race case may happen, result in use after free issue.

- f2fs_iget
 - do_read_inode
  - f2fs_init_read_extent_tree
  : add largest extent entry in to cache
					- shrink
					 - f2fs_shrink_read_extent_tree
					  - __shrink_extent_tree
					   - __detach_extent_node
					   : drop largest extent entry
  - sanity_check_extent_cache
  : access et->largest w/o lock

let's refactor sanity_check_extent_cache() to avoid extent cache access
and call it before f2fs_init_read_extent_tree() to fix this issue.

The Linux kernel CVE team has assigned CVE-2024-44941 to this issue.

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

	Fixed in 6.6.47 with commit 263df78166d3
	Fixed in 6.10.6 with commit 323ef20b5558
	Fixed in 6.11 with commit d7409b05a64f

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-2024-44941
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/extent_cache.c
	fs/f2fs/f2fs.h
	fs/f2fs/inode.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/263df78166d3a9609b97d28c34029bd01874cbb8
	https://git.kernel.org/stable/c/323ef20b5558b9d9fd10c1224327af6f11a8177d
	https://git.kernel.org/stable/c/d7409b05a64f212735f0d33f5f1602051a886eab