Subject: CVE-2024-42111: btrfs: always do the basic checks for btrfs_qgroup_inherit structure

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

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

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

btrfs: always do the basic checks for btrfs_qgroup_inherit structure

[BUG]
Syzbot reports the following regression detected by KASAN:

  BUG: KASAN: slab-out-of-bounds in btrfs_qgroup_inherit+0x42e/0x2e20 fs/btrfs/qgroup.c:3277
  Read of size 8 at addr ffff88814628ca50 by task syz-executor318/5171

  CPU: 0 PID: 5171 Comm: syz-executor318 Not tainted 6.10.0-rc2-syzkaller-00010-g2ab795141095 #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
  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
   btrfs_qgroup_inherit+0x42e/0x2e20 fs/btrfs/qgroup.c:3277
   create_pending_snapshot+0x1359/0x29b0 fs/btrfs/transaction.c:1854
   create_pending_snapshots+0x195/0x1d0 fs/btrfs/transaction.c:1922
   btrfs_commit_transaction+0xf20/0x3740 fs/btrfs/transaction.c:2382
   create_snapshot+0x6a1/0x9e0 fs/btrfs/ioctl.c:875
   btrfs_mksubvol+0x58f/0x710 fs/btrfs/ioctl.c:1029
   btrfs_mksnapshot+0xb5/0xf0 fs/btrfs/ioctl.c:1075
   __btrfs_ioctl_snap_create+0x387/0x4b0 fs/btrfs/ioctl.c:1340
   btrfs_ioctl_snap_create_v2+0x1f2/0x3a0 fs/btrfs/ioctl.c:1422
   btrfs_ioctl+0x99e/0xc60
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:907 [inline]
   __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  RIP: 0033:0x7fcbf1992509
  RSP: 002b:00007fcbf1928218 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
  RAX: ffffffffffffffda RBX: 00007fcbf1a1f618 RCX: 00007fcbf1992509
  RDX: 0000000020000280 RSI: 0000000050009417 RDI: 0000000000000003
  RBP: 00007fcbf1a1f610 R08: 00007ffea1298e97 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000246 R12: 00007fcbf19eb660
  R13: 00000000200002b8 R14: 00007fcbf19e60c0 R15: 0030656c69662f2e
   </TASK>

And it also pinned it down to commit b5357cb268c4 ("btrfs: qgroup: do not
check qgroup inherit if qgroup is disabled").

[CAUSE]
That offending commit skips the whole qgroup inherit check if qgroup is
not enabled.

But that also skips the very basic checks like
num_ref_copies/num_excl_copies and the structure size checks.

Meaning if a qgroup enable/disable race is happening at the background,
and we pass a btrfs_qgroup_inherit structure when the qgroup is
disabled, the check would be completely skipped.

Then at the time of transaction commitment, qgroup is re-enabled and
btrfs_qgroup_inherit() is going to use the incorrect structure and
causing the above KASAN error.

[FIX]
Make btrfs_qgroup_check_inherit() only skip the source qgroup checks.
So that even if invalid btrfs_qgroup_inherit structure is passed in, we
can still reject invalid ones no matter if qgroup is enabled or not.

Furthermore we do already have an extra safety inside
btrfs_qgroup_inherit(), which would just ignore invalid qgroup sources,
so even if we only skip the qgroup source check we're still safe.

The Linux kernel CVE team has assigned CVE-2024-42111 to this issue.

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

	Issue introduced in 6.9 with commit b5357cb268c4 and fixed in 6.9.9 with commit ebe5ea02577b
	Issue introduced in 6.9 with commit b5357cb268c4 and fixed in 6.10 with commit 724d8042cef8
	Issue introduced in 6.8.10 with commit c839f73a70f3

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-2024-42111
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/btrfs/qgroup.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/ebe5ea02577b2c527958af1b76ac472c7ab53a56
	https://git.kernel.org/stable/c/724d8042cef84496ddb4492dc120291f997ae26b