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CVE-2022-48920· NVD / CVE Program· CNA Linux

btrfs: get rid of warning on transaction commit when using flushoncommit

In the Linux kernel, the following vulnerability has been resolved: btrfs: get rid of warning on transaction commit when using flushoncommit When using the flushoncommit mount option, during almost every transaction commit we trigger a warning from __writeback_inodes_sb_nr(): $ cat fs/fs-writeback.c: (...) static void __writeback_inodes_sb_nr(struct super_block *sb, ... { (...) WARN_ON(!rwsem_is_locked(&sb->s_umount)); (...) } (...) The trace produced in dmesg looks like the following: [947.473890] WARNING: CPU: 5 PID: 930 at fs/fs-writeback.c:2610 __writeback_inodes_sb_nr+0x7e/0xb3 [947.481623] Modules linked in: nfsd nls_cp437 cifs asn1_decoder cifs_arc4 fscache cifs_md4 ipmi_ssif [947.489571] CPU: 5 PID: 930 Comm: btrfs-transacti Not tainted 95.16.3-srb-asrock-00001-g36437ad63879 #186 [947.497969] RIP: 0010:__writeback_inodes_sb_nr+0x7e/0xb3 [947.502097] Code: 24 10 4c 89 44 24 18 c6 (...) [947.519760] RSP: 0018:ffffc90000777e10 EFLAGS: 00010246 [947.523818] RAX: 0000000000000000 RBX: 0000000000963300 RCX: 0000000000000000 [947.529765] RDX: 0000000000000000 RSI: 000000000000fa51 RDI: ffffc90000777e50 [947.535740] RBP: ffff888101628a90 R08: ffff888100955800 R09: ffff888100956000 [947.541701] R10: 0000000000000002 R11: 0000000000000001 R12: ffff888100963488 [947.547645] R13: ffff888100963000 R14: ffff888112fb7200 R15: ffff888100963460 [947.553621] FS: 0000000000000000(0000) GS:ffff88841fd40000(0000) knlGS:0000000000000000 [947.560537] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [947.565122] CR2: 0000000008be50c4 CR3: 000000000220c000 CR4: 00000000001006e0 [947.571072] Call Trace: [947.572354] <TASK> [947.573266] btrfs_commit_transaction+0x1f1/0x998 [947.576785] ? start_transaction+0x3ab/0x44e [947.579867] ? schedule_timeout+0x8a/0xdd [947.582716] transaction_kthread+0xe9/0x156 [947.585721] ? btrfs_cleanup_transaction.isra.0+0x407/0x407 [947.590104] kthread+0x131/0x139 [947.592168] ? set_kthread_struct+0x32/0x32 [947.595174] ret_from_fork+0x22/0x30 [947.597561] </TASK> [947.598553] ---[ end trace 644721052755541c ]--- This is because we started using writeback_inodes_sb() to flush delalloc when committing a transaction (when using -o flushoncommit), in order to avoid deadlocks with filesystem freeze operations. This change was made by commit ce8ea7cc6eb313 ("btrfs: don't call btrfs_start_delalloc_roots in flushoncommit"). After that change we started producing that warning, and every now and then a user reports this since the warning happens too often, it spams dmesg/syslog, and a user is unsure if this reflects any problem that might compromise the filesystem's reliability. We can not just lock the sb->s_umount semaphore before calling writeback_inodes_sb(), because that would at least deadlock with filesystem freezing, since at fs/super.c:freeze_super() sync_filesystem() is called while we are holding that semaphore in write mode, and that can trigger a transaction commit, resulting in a deadlock. It would also trigger the same type of deadlock in the unmount path. Possibly, it could also introduce some other locking dependencies that lockdep would report. To fix this call try_to_writeback_inodes_sb() instead of writeback_inodes_sb(), because that will try to read lock sb->s_umount and then will only call writeback_inodes_sb() if it was able to lock it. This is fine because the cases where it can't read lock sb->s_umount are during a filesystem unmount or during a filesystem freeze - in those cases sb->s_umount is write locked and sync_filesystem() is called, which calls writeback_inodes_sb(). In other words, in all cases where we can't take a read lock on sb->s_umount, writeback is already being triggered elsewhere. An alternative would be to call btrfs_start_delalloc_roots() with a number of pages different from LONG_MAX, for example matching the number of delalloc bytes we currently have, in ---truncated---

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
Aug 21, 2024
Updated
Jun 17, 2026
EPSS
0.2% · 5th percentile
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JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Affected systems

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernelbefore 5.15.27
  • linux linux kernel5.16 and later · before 5.16.13
  • linux linux kernel5.17

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4.15affected
    • ce8ea7cc6eb3139f4c730d647325e69354159b0f and later · before 850a77c999b81dd2724efd2684068d6f90db8c16affected · git
    • ce8ea7cc6eb3139f4c730d647325e69354159b0f and later · before e4d044dbffcd570351f21c747fc77ff90aed7f2eaffected · git
    • ce8ea7cc6eb3139f4c730d647325e69354159b0f and later · before a0f0cf8341e34e5d2265bfd3a7ad68342da1e2aaaffected · git
    • before 4.15not affected · semver
    • 5.15.27 and later · up to and including 5.15.*not affected · semver
    • 5.16.13 and later · up to and including 5.16.*not affected · semver
    • 5.17 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.16.14-15.16.14-1
SUSE:Linux Enterprise High Availability Extension 12 SP5kernel-defaultbefore 4.12.14-122.228.14.12.14-122.228.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_60before 1-8.3.11-8.3.1
SUSE:Linux Enterprise Real Time 12 SP5kernel-rtbefore 4.12.14-10.200.14.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5kernel-rt_debugbefore 4.12.14-10.200.14.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5kernel-source-rtbefore 4.12.14-10.200.14.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5kernel-syms-rtbefore 4.12.14-10.200.14.12.14-10.200.1
SUSE:Linux Enterprise Server 12 SP5kernel-azurebefore 4.12.14-16.197.14.12.14-16.197.1
SUSE:Linux Enterprise Server 12 SP5kernel-sourcebefore 4.12.14-122.228.14.12.14-122.228.1
SUSE:Linux Enterprise Server 12 SP5kernel-source-azurebefore 4.12.14-16.197.14.12.14-16.197.1
SUSE:Linux Enterprise Server 12 SP5kernel-symsbefore 4.12.14-122.228.14.12.14-122.228.1
SUSE:Linux Enterprise Server 12 SP5kernel-syms-azurebefore 4.12.14-16.197.14.12.14-16.197.1
SUSE:Linux Enterprise Software Development Kit 12 SP5kernel-docsbefore 4.12.14-122.228.24.12.14-122.228.2
SUSE:Linux Enterprise Software Development Kit 12 SP5kernel-obs-buildbefore 4.12.14-122.228.24.12.14-122.228.2

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Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux850a77c999b81dd2724efd2684068d6f90db8c16Vendor (CNA)
Linux Linuxa0f0cf8341e34e5d2265bfd3a7ad68342da1e2aaVendor (CNA)
Linux Linuxe4d044dbffcd570351f21c747fc77ff90aed7f2eVendor (CNA)
debian:linux5.16.14-1 · Debian:12Package registry (OSV)
suse:kernel-azure4.12.14-16.197.1 · SUSE:Linux Enterprise Server 12 SP5Package registry (OSV)
suse:kernel-default4.12.14-122.228.1 · SUSE:Linux Enterprise High Availability Extension 12 SP5Package registry (OSV)
suse:kernel-docs4.12.14-122.228.2 · SUSE:Linux Enterprise Software Development Kit 12 SP5Package registry (OSV)
suse:kernel-obs-build4.12.14-122.228.2 · SUSE:Linux Enterprise Software Development Kit 12 SP5Package registry (OSV)
suse:kernel-rt4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5Package registry (OSV)
suse:kernel-rt_debug4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5Package registry (OSV)
suse:kernel-source4.12.14-122.228.1 · SUSE:Linux Enterprise Server 12 SP5Package registry (OSV)
suse:kernel-source-azure4.12.14-16.197.1 · SUSE:Linux Enterprise Server 12 SP5Package registry (OSV)
suse:kernel-source-rt4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5Package registry (OSV)
suse:kernel-syms4.12.14-122.228.1 · SUSE:Linux Enterprise Server 12 SP5Package registry (OSV)
suse:kernel-syms-rt4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5Package registry (OSV)
suse:kgraft-patch-SLE12-SP5_Update_601-8.3.1 · SUSE:Linux Enterprise Live Patching 12 SP5Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-667 · Improper Locking

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Noroxi analysis

No Noroxi analysis for this record yet

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Change log

  1. Fix✗ → ✓

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References

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