linux-cve-announce - CVE-2024-56758: btrfs: check folio mapping after unlock in relocate_one

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Message-ID: <2025010653-CVE-2024-56758-eeb6@gregkh>
Date: Mon,  6 Jan 2025 17:20:52 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56758: btrfs: check folio mapping after unlock in relocate_one_folio()

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

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

btrfs: check folio mapping after unlock in relocate_one_folio()

When we call btrfs_read_folio() to bring a folio uptodate, we unlock the
folio. The result of that is that a different thread can modify the
mapping (like remove it with invalidate) before we call folio_lock().
This results in an invalid page and we need to try again.

In particular, if we are relocating concurrently with aborting a
transaction, this can result in a crash like the following:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP
  CPU: 76 PID: 1411631 Comm: kworker/u322:5
  Workqueue: events_unbound btrfs_reclaim_bgs_work
  RIP: 0010:set_page_extent_mapped+0x20/0xb0
  RSP: 0018:ffffc900516a7be8 EFLAGS: 00010246
  RAX: ffffea009e851d08 RBX: ffffea009e0b1880 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: ffffc900516a7b90 RDI: ffffea009e0b1880
  RBP: 0000000003573000 R08: 0000000000000001 R09: ffff88c07fd2f3f0
  R10: 0000000000000000 R11: 0000194754b575be R12: 0000000003572000
  R13: 0000000003572fff R14: 0000000000100cca R15: 0000000005582fff
  FS:  0000000000000000(0000) GS:ffff88c07fd00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 000000407d00f002 CR4: 00000000007706f0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  PKRU: 55555554
  Call Trace:
  <TASK>
  ? __die+0x78/0xc0
  ? page_fault_oops+0x2a8/0x3a0
  ? __switch_to+0x133/0x530
  ? wq_worker_running+0xa/0x40
  ? exc_page_fault+0x63/0x130
  ? asm_exc_page_fault+0x22/0x30
  ? set_page_extent_mapped+0x20/0xb0
  relocate_file_extent_cluster+0x1a7/0x940
  relocate_data_extent+0xaf/0x120
  relocate_block_group+0x20f/0x480
  btrfs_relocate_block_group+0x152/0x320
  btrfs_relocate_chunk+0x3d/0x120
  btrfs_reclaim_bgs_work+0x2ae/0x4e0
  process_scheduled_works+0x184/0x370
  worker_thread+0xc6/0x3e0
  ? blk_add_timer+0xb0/0xb0
  kthread+0xae/0xe0
  ? flush_tlb_kernel_range+0x90/0x90
  ret_from_fork+0x2f/0x40
  ? flush_tlb_kernel_range+0x90/0x90
  ret_from_fork_asm+0x11/0x20
  </TASK>

This occurs because cleanup_one_transaction() calls
destroy_delalloc_inodes() which calls invalidate_inode_pages2() which
takes the folio_lock before setting mapping to NULL. We fail to check
this, and subsequently call set_extent_mapping(), which assumes that
mapping != NULL (in fact it asserts that in debug mode)

Note that the "fixes" patch here is not the one that introduced the
race (the very first iteration of this code from 2009) but a more recent
change that made this particular crash happen in practice.

The Linux kernel CVE team has assigned CVE-2024-56758 to this issue.


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

	Issue introduced in 6.6 with commit e7f1326cc24e22b38afc3acd328480a1183f9e79 and fixed in 6.12.8 with commit d508e56270389b3a16f5b3cf247f4eb1bbad1578
	Issue introduced in 6.6 with commit e7f1326cc24e22b38afc3acd328480a1183f9e79 and fixed in 6.13-rc5 with commit 3e74859ee35edc33a022c3f3971df066ea0ca6b9
	Issue introduced in 6.1.54 with commit 08daa38ca212d87f77beae839bc9be71079c7abf
	Issue introduced in 6.5.4 with commit 9d1e020ed9649cf140fcfafd052cfdcce9e9d67d

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-2024-56758
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/relocation.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/d508e56270389b3a16f5b3cf247f4eb1bbad1578
	https://git.kernel.org/stable/c/3e74859ee35edc33a022c3f3971df066ea0ca6b9