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Fencer Intel
medium 5.5

CVE-2024-49868 json

btrfs: fix a NULL pointer dereference when failed to start a new trasacntion

published 2y ago modified 4mo ago also EUVD-2024-43781

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 21%
public exploits
0
none known

Summary

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

btrfs: fix a NULL pointer dereference when failed to start a new trasacntion

[BUG] Syzbot reported a NULL pointer dereference with the following crash:

FAULT_INJECTION: forcing a failure. start_transaction+0x830/0x1670 fs/btrfs/transaction.c:676 prepare_to_relocate+0x31f/0x4c0 fs/btrfs/relocation.c:3642 relocate_block_group+0x169/0xd20 fs/btrfs/relocation.c:3678 ... BTRFS info (device loop0): balance: ended with status: -12 Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cc: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000660-0x0000000000000667] RIP: 0010:btrfs_update_reloc_root+0x362/0xa80 fs/btrfs/relocation.c:926 Call Trace: <TASK> commit_fs_roots+0x2ee/0x720 fs/btrfs/transaction.c:1496 btrfs_commit_transaction+0xfaf/0x3740 fs/btrfs/transaction.c:2430 del_balance_item fs/btrfs/volumes.c:3678 [inline] reset_balance_state+0x25e/0x3c0 fs/btrfs/volumes.c:3742 btrfs_balance+0xead/0x10c0 fs/btrfs/volumes.c:4574 btrfs_ioctl_balance+0x493/0x7c0 fs/btrfs/ioctl.c:3673 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 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

[CAUSE] The allocation failure happens at the start_transaction() inside prepare_to_relocate(), and during the error handling we call unset_reloc_control(), which makes fs_info->balance_ctl to be NULL.

Then we continue the error path cleanup in btrfs_balance() by calling reset_balance_state() which will call del_balance_item() to fully delete the balance item in the root tree.

However during the small window between set_reloc_contrl() and unset_reloc_control(), we can have a subvolume tree update and created a reloc_root for that subvolume.

Then we go into the final btrfs_commit_transaction() of del_balance_item(), and into btrfs_update_reloc_root() inside commit_fs_roots().

That function checks if fs_info->reloc_ctl is in the merge_reloc_tree stage, but since fs_info->reloc_ctl is NULL, it results a NULL pointer dereference.

[FIX] Just add extra check on fs_info->reloc_ctl inside btrfs_update_reloc_root(), before checking fs_info->reloc_ctl->merge_reloc_tree.

That DEAD_RELOC_TREE handling is to prevent further modification to the reloc tree during merge stage, but since there is no reloc_ctl at all, we do not need to bother that.

Patch / fix

  • Linux Linux 5.4.285, 5.10.227, 5.15.168, 6.1.113, 6.6.55, 6.10.14, 6.11.3, 6.12
  • linux Debian 12 6.1.115-1
  • linux Debian 14, Debian 13 6.11.4-1

debian advisories DEBIAN-CVE-2024-49868

  • linux Ubuntu 20.04 LTS 5.4.0-208.228
  • linux Ubuntu 22.04 LTS 5.15.0-127.137
  • linux Ubuntu 24.04 LTS 6.8.0-54.56
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1140.150
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1073.79
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1023.25
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1143.152
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1072.80

ubuntu advisories UBUNTU-CVE-2024-49868

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-source Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1
  • kernel-default Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1
  • kernel-kvmsmall Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1
  • kernel-default-base Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1.21.4
  • kernel-livepatch-MICRO-6-0_Update_4 Linux Micro 6.1, Linux Micro 6.0 1-1.2
  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-22.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-22.1
  • kernel-livepatch-MICRO-6-0-RT_Update_4 Linux Micro 6.1, Linux Micro 6.0 1-1.1

suse advisories SUSE-SU-2025:20164-1SUSE-SU-2025:20247-1SUSE-SU-2025:20163-1SUSE-SU-2025:20246-1SUSE-SU-2025:0035-1SUSE-SU-2024:4387-1

  • kernel-source-longterm openSUSE Tumbleweed 6.12.11-1.1
  • kernel-source openSUSE Tumbleweed 6.11.8-1.1

opensuse advisories openSUSE-SU-2025:14705-1openSUSE-SU-2024:14500-1

  • kernel CBL-Mariner 2.0 5.15.173.1-1

azure linux advisories AZL-51405

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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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-2024-49868 updated cvss 5.5

kernel: btrfs: fix a NULL pointer dereference when failed to start a new trasacntion

  • 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: 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 ICSA-25-226-07 updated

Siemens Third-Party Components in SINEC OS

  • Siemens RUGGEDCOM RST2428P (6GK6242-6PA00) Siemens SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family Siemens SCALANCE XCM-/XRM-/XCH-/XRH-300 family
    not affected

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2y ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 21% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
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

Weakness
Technology feeds

References

Sources

Fencer Intel 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.