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Fencer Vulns
medium 4.7

CVE-2023-52896 json

btrfs: fix race between quota rescan and disable leading to NULL pointer deref

published 2024-08-21 2 y ago modified 2026-06-17 4 mo ago also EUVD-2023-59607

cvss
4.7
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

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

btrfs: fix race between quota rescan and disable leading to NULL pointer deref

If we have one task trying to start the quota rescan worker while another one is trying to disable quotas, we can end up hitting a race that results in the quota rescan worker doing a NULL pointer dereference. The steps for this are the following:

1) Quotas are enabled;

2) Task A calls the quota rescan ioctl and enters btrfs_qgroup_rescan(). It calls qgroup_rescan_init() which returns 0 (success) and then joins a transaction and commits it;

3) Task B calls the quota disable ioctl and enters btrfs_quota_disable(). It clears the bit BTRFS_FS_QUOTA_ENABLED from fs_info->flags and calls btrfs_qgroup_wait_for_completion(), which returns immediately since the rescan worker is not yet running. Then it starts a transaction and locks fs_info->qgroup_ioctl_lock;

4) Task A queues the rescan worker, by calling btrfs_queue_work();

5) The rescan worker starts, and calls rescan_should_stop() at the start of its while loop, which results in 0 iterations of the loop, since the flag BTRFS_FS_QUOTA_ENABLED was cleared from fs_info->flags by task B at step 3);

6) Task B sets fs_info->quota_root to NULL;

7) The rescan worker tries to start a transaction and uses fs_info->quota_root as the root argument for btrfs_start_transaction(). This results in a NULL pointer dereference down the call chain of btrfs_start_transaction(). The stack trace is something like the one reported in Link tag below:

general protection fault, probably for non-canonical address 0xdffffc0000000041: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000208-0x000000000000020f] CPU: 1 PID: 34 Comm: kworker/u4:2 Not tainted 6.1.0-syzkaller-13872-gb6bb9676f216 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022 Workqueue: btrfs-qgroup-rescan btrfs_work_helper RIP: 0010:start_transaction+0x48/0x10f0 fs/btrfs/transaction.c:564 Code: 48 89 fb 48 (...) RSP: 0018:ffffc90000ab7ab0 EFLAGS: 00010206 RAX: 0000000000000041 RBX: 0000000000000208 RCX: ffff88801779ba80 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 RBP: dffffc0000000000 R08: 0000000000000001 R09: fffff52000156f5d R10: fffff52000156f5d R11: 1ffff92000156f5c R12: 0000000000000000 R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000003 FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2bea75b718 CR3: 000000001d0cc000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> btrfs_qgroup_rescan_worker+0x3bb/0x6a0 fs/btrfs/qgroup.c:3402 btrfs_work_helper+0x312/0x850 fs/btrfs/async-thread.c:280 process_one_work+0x877/0xdb0 kernel/workqueue.c:2289 worker_thread+0xb14/0x1330 kernel/workqueue.c:2436 kthread+0x266/0x300 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 </TASK> Modules linked in:

So fix this by having the rescan worker function not attempt to start a transaction if it didn't do any rescan work.

Patch / fix

  • Linux Linux 5.4.230, 5.10.165, 5.15.90, 5.17, 6.1.8, 6.2
  • linux Debian 14, Debian 13, Debian 12 6.1.8-1

debian advisories DEBIAN-CVE-2023-52896

  • linux Ubuntu 20.04 LTS 5.4.0-147.164
  • linux Ubuntu 22.04 LTS 5.15.0-70.77
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1100.108
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1034.38
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1103.112
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1032.40
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1031.36
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1047.52

ubuntu advisories UBUNTU-CVE-2023-52896

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

  • dtb-aarch64 openSUSE Leap 15.5 5.14.21-150500.55.80.1
  • kernel-64kb SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.80.2
  • kernel-syms SLE Module for Development Tools 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.80.1
  • kernel-obs-qa openSUSE Leap 15.5 5.14.21-150500.55.80.1
  • kernel-source SLE Module for Development Tools 15 SP5, SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.80.2
  • kernel-default SLE Workstation Extension 15 SP5, SLE Module for Legacy 15 SP5, SLE Module for Basesystem 15 SP5 +5 more 5.14.21-150500.55.80.2
  • kernel-kvmsmall openSUSE Leap 15.5 5.14.21-150500.55.80.2
  • kernel-zfcpdump SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.80.2

suse advisories SUSE-SU-2024:3483-1SUSE-SU-2024:3408-1SUSE-SU-2024:3227-1SUSE-SU-2024:3209-1SUSE-SU-2024:3190-1

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-2023-52896 updated cvss 4.7

kernel: btrfs: fix race between quota rescan and disable leading to NULL pointer deref

  • 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 SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
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.