Subject: CVE-2024-27070: f2fs: fix to avoid use-after-free issue in f2fs_filemap_fault

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

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

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

f2fs: fix to avoid use-after-free issue in f2fs_filemap_fault

syzbot reports a f2fs bug as below:

BUG: KASAN: slab-use-after-free in f2fs_filemap_fault+0xd1/0x2c0 fs/f2fs/file.c:49
Read of size 8 at addr ffff88807bb22680 by task syz-executor184/5058

CPU: 0 PID: 5058 Comm: syz-executor184 Not tainted 6.7.0-syzkaller-09928-g052d534373b7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x163/0x540 mm/kasan/report.c:488
 kasan_report+0x142/0x170 mm/kasan/report.c:601
 f2fs_filemap_fault+0xd1/0x2c0 fs/f2fs/file.c:49
 __do_fault+0x131/0x450 mm/memory.c:4376
 do_shared_fault mm/memory.c:4798 [inline]
 do_fault mm/memory.c:4872 [inline]
 do_pte_missing mm/memory.c:3745 [inline]
 handle_pte_fault mm/memory.c:5144 [inline]
 __handle_mm_fault+0x23b7/0x72b0 mm/memory.c:5285
 handle_mm_fault+0x27e/0x770 mm/memory.c:5450
 do_user_addr_fault arch/x86/mm/fault.c:1364 [inline]
 handle_page_fault arch/x86/mm/fault.c:1507 [inline]
 exc_page_fault+0x456/0x870 arch/x86/mm/fault.c:1563
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570

The root cause is: in f2fs_filemap_fault(), vmf->vma may be not alive after
filemap_fault(), so it may cause use-after-free issue when accessing
vmf->vma->vm_flags in trace_f2fs_filemap_fault(). So it needs to keep vm_flags
in separated temporary variable for tracepoint use.

The Linux kernel CVE team has assigned CVE-2024-27070 to this issue.

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

	Issue introduced in 6.8 with commit 87f3afd366f7 and fixed in 6.8.2 with commit 8186e16a766d
	Issue introduced in 6.8 with commit 87f3afd366f7 and fixed in 6.9 with commit eb70d5a6c932

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-2024-27070
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/file.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/8186e16a766d709a08f188d2f4e84098f364bea1
	https://git.kernel.org/stable/c/eb70d5a6c932d9d23f4bb3e7b83782c21ac4b064