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Fencer Vulns
high 7.8

CVE-2024-42103 json

btrfs: fix adding block group to a reclaim list and the unused list during reclaim

published 2024-07-30 2 y ago modified 2026-08-05 3 mo ago also EUVD-2024-39935

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

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

btrfs: fix adding block group to a reclaim list and the unused list during reclaim

There is a potential parallel list adding for retrying in btrfs_reclaim_bgs_work and adding to the unused list. Since the block group is removed from the reclaim list and it is on a relocation work, it can be added into the unused list in parallel. When that happens, adding it to the reclaim list will corrupt the list head and trigger list corruption like below.

Fix it by taking fs_info->unused_bgs_lock.

[177.504][T2585409] BTRFS error (device nullb1): error relocating ch= unk 2415919104 [177.514][T2585409] list_del corruption. next->prev should be ff1100= 0344b119c0, but was ff11000377e87c70. (next=3Dff110002390cd9c0) [177.529][T2585409] ------------[ cut here ]------------ [177.537][T2585409] kernel BUG at lib/list_debug.c:65! [177.545][T2585409] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI [177.555][T2585409] CPU: 9 PID: 2585409 Comm: kworker/u128:2 Tainted: G W 6.10.0-rc5-kts #1 [177.568][T2585409] Hardware name: Supermicro SYS-520P-WTR/X12SPW-TF, BIOS 1.2 02/14/2022 [177.579][T2585409] Workqueue: events_unbound btrfs_reclaim_bgs_work[btrfs] [177.589][T2585409] RIP: 0010:__list_del_entry_valid_or_report.cold+0x70/0x72 [177.624][T2585409] RSP: 0018:ff11000377e87a70 EFLAGS: 00010286 [177.633][T2585409] RAX: 000000000000006d RBX: ff11000344b119c0 RCX:0000000000000000 [177.644][T2585409] RDX: 000000000000006d RSI: 0000000000000008 RDI:ffe21c006efd0f40 [177.655][T2585409] RBP: ff110002e0509f78 R08: 0000000000000001 R09:ffe21c006efd0f08 [177.665][T2585409] R10: ff11000377e87847 R11: 0000000000000000 R12:ff110002390cd9c0 [177.676][T2585409] R13: ff11000344b119c0 R14: ff110002e0508000 R15:dffffc0000000000 [177.687][T2585409] FS: 0000000000000000(0000) GS:ff11000fec880000(0000) knlGS:0000000000000000 [177.700][T2585409] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [177.709][T2585409] CR2: 00007f06bc7b1978 CR3: 0000001021e86005 CR4:0000000000771ef0 [177.720][T2585409] DR0: 0000000000000000 DR1: 0000000000000000 DR2:0000000000000000 [177.731][T2585409] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:0000000000000400 [177.742][T2585409] PKRU: 55555554 [177.748][T2585409] Call Trace: [177.753][T2585409] <TASK> [177.759][T2585409] ? __die_body.cold+0x19/0x27 [177.766][T2585409] ? die+0x2e/0x50 [177.772][T2585409] ? do_trap+0x1ea/0x2d0 [177.779][T2585409] ? __list_del_entry_valid_or_report.cold+0x70/0x72 [177.788][T2585409] ? do_error_trap+0xa3/0x160 [177.795][T2585409] ? __list_del_entry_valid_or_report.cold+0x70/0x72 [177.805][T2585409] ? handle_invalid_op+0x2c/0x40 [177.812][T2585409] ? __list_del_entry_valid_or_report.cold+0x70/0x72 [177.820][T2585409] ? exc_invalid_op+0x2d/0x40 [177.827][T2585409] ? asm_exc_invalid_op+0x1a/0x20 [177.834][T2585409] ? __list_del_entry_valid_or_report.cold+0x70/0x72 [177.843][T2585409] btrfs_delete_unused_bgs+0x3d9/0x14c0 [btrfs]

There is a similar retry_list code in btrfs_delete_unused_bgs(), but it is safe, AFAICS. Since the block group was in the unused list, the used bytes should be 0 when it was added to the unused list. Then, it checks block_group->{used,reserved,pinned} are still 0 under the block_group->lock. So, they should be still eligible for the unused list, not the reclaim list.

The reason it is safe there it's because because we're holding space_info->groups_sem in write mode.

That means no other task can allocate from the block group, so while we are at deleted_unused_bgs() it's not possible for other tasks to allocate and deallocate extents from the block group, so it can't be added to the unused list or the reclaim list by anyone else.

The bug can be reproduced by btrfs/166 after a few rounds. In practice this can be hit when relocation cannot find more chunk space and ends with ENOSPC.

Patch / fix

  • Linux Linux 5.15.163, 6.1.98, 6.6.39, 6.9.9
  • linux Debian 12 6.1.98-1
  • linux Debian 14, Debian 13 6.9.9-1

debian advisories DEBIAN-CVE-2024-42103

  • linux Ubuntu 24.04 LTS 6.8.0-48.48
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1018.20
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1017.19
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1013.17
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1015.15
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1017.20
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1002.4
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1014.16

ubuntu advisories UBUNTU-CVE-2024-42103

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-40.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-40.1
  • kernel-source Linux Micro 6.1, Linux Micro 6.0 6.4.0-39.1
  • kernel-default Linux Micro 6.1, Linux Micro 6.0 6.4.0-39.1
  • kernel-kvmsmall Linux Micro 6.1, Linux Micro 6.0 6.4.0-39.1
  • kernel-default-base Linux Micro 6.1, Linux Micro 6.0 6.4.0-39.1.21.16
  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.31.2
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.31.1

suse advisories SUSE-SU-2026:20845-1SUSE-SU-2026:20876-1SUSE-SU-2026:20477-1SUSE-SU-2026:20498-1SUSE-SU-2026:0587-1SUSE-SU-2026:0472-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2024-42103 updated cvss 5.3

kernel: btrfs: fix adding block group to a reclaim list and the unused list during reclaim

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.