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🛡️ CVE-2024-56758 — kernel

🟡 CVSS 5.5 — Medium ✅ No Known Exploit NVD
5.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

btrfs: check folio mapping after unlock in relocate_one_folio()

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.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Affected software

CVE-2024-56758 is recorded against 2 packages.

  • kernel (from 6.6.0 up to 6.12.8)
  • linux-kernel

Timeline and source

Published on 6 January 2025 and last revised on 12 August 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
lists.debian.org (Web)
github.com (Advisory)
nvd.nist.gov (Advisory)
git.kernel.org (Package)

Other advisories for this package

kernel has other advisories on record. If you are patching this one, these are worth checking on the same host:

CVE-2024-56758 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Medium
CVSS Score 5.5
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE N/A
Public Exploit ✅ No
Source NVD
Published 2025-01-06
Updated 2026-08-20
Modified 2026-08-12

Affected Packages

Software From version Fixed in
kernel 6.6.0 6.12.8
linux-kernel — —

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