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CVE Record

CVE-2021-47145: btrfs: do not BUG_ON in link_to_fixup_dir

In the Linux kernel, the following vulnerability has been resolved: btrfs: do not BUG_ON in link_to_fixup_dir While doing error injection testing I got the following panic kernel BUG at fs/btrfs/tree-log.c:1862! invalid opcode: 0000 [#1] SMP NOPTI CPU: 1 PID: 7836 Comm: mount Not tainted 5.13.0-rc1+ #305 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 RIP: 0010:link_to_fixup_dir+0xd5/0xe0 RSP: 0018:ffffb5800180fa30 EFLAGS: 00010216 RAX: fffffffffffffffb RBX: 00000000fffffffb RCX: ffff8f595287faf0 RDX: ffffb5800180fa37 RSI: ffff8f5954978800 RDI: 0000000000000000 RBP: ffff8f5953af9450 R08: 0000000000000019 R09: 0000000000000001 R10: 000151f408682970 R11: 0000000120021001 R12: ffff8f5954978800 R13: ffff8f595287faf0 R14: ffff8f5953c77dd0 R15: 0000000000000065 FS: 00007fc5284c8c40(0000) GS:ffff8f59bbd00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fc5287f47c0 CR3: 000000011275e002 CR4: 0000000000370ee0 Call Trace: replay_one_buffer+0x409/0x470 ? btree_read_extent_buffer_pages+0xd0/0x110 walk_up_log_tree+0x157/0x1e0 walk_log_tree+0xa6/0x1d0 btrfs_recover_log_trees+0x1da/0x360 ? replay_one_extent+0x7b0/0x7b0 open_ctree+0x1486/0x1720 btrfs_mount_root.cold+0x12/0xea ? __kmalloc_track_caller+0x12f/0x240 legacy_get_tree+0x24/0x40 vfs_get_tree+0x22/0xb0 vfs_kern_mount.part.0+0x71/0xb0 btrfs_mount+0x10d/0x380 ? vfs_parse_fs_string+0x4d/0x90 legacy_get_tree+0x24/0x40 vfs_get_tree+0x22/0xb0 path_mount+0x433/0xa10 __x64_sys_mount+0xe3/0x120 do_syscall_64+0x3d/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae We can get -EIO or any number of legitimate errors from btrfs_search_slot(), panicing here is not the appropriate response. The error path for this code handles errors properly, simply return the error.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Linux kernel Btrfs bug can turn recoverable filesystem errors into a kernel panic during mount-time log recovery. For businesses, the main concern is availability: affected Btrfs systems may crash instead of handling an error cleanly. The supplied sources do not show active exploitation or a CVSS score.

Executive priority

Treat as a normal-priority availability fix unless critical Btrfs-backed systems are exposed. Escalate patching for infrastructure where an unexpected kernel panic would cause material outage or recovery delays.

Technical view

In Btrfs tree-log recovery, link_to_fixup_dir used BUG_ON after btrfs_search_slot returned legitimate errors such as EIO. The fix changes the behavior to return the error through the existing error path instead of panicking. Evidence points to a kernel availability defect, not disclosed privilege escalation or remote execution.

Likely exposure

Exposure is likely limited to Linux systems using Btrfs on affected kernel versions or vendor builds missing the referenced stable fixes. Systems not using Btrfs are unlikely to be exposed based on the supplied evidence.

Exploitation context

The source describes error-injection testing causing a panic during mount. The supplied bundle marks KEV as false and provides no cited evidence of active exploitation, public weaponization, or remote triggering.

Researcher notes

The record lacks CVSS, CWE, and exploit evidence. Analysis should stay centered on Btrfs error handling during log replay. The commit references are the strongest remediation evidence; distribution package mapping still requires vendor-specific confirmation.

Mitigation direction

  • Update affected Linux kernels through the relevant distribution or vendor channel.
  • Prioritize hosts that use Btrfs for root, data, or mounted volumes.
  • Confirm the installed kernel includes the referenced stable Btrfs fix.
  • Follow vendor advisories for exact fixed package versions.
  • Plan reboot windows where kernel updates require restart.

Validation and detection

  • Inventory systems using Btrfs filesystems.
  • Compare running kernel builds against vendor fixed versions or stable commits.
  • Review kernel changelogs for "btrfs: do not BUG_ON in link_to_fixup_dir".
  • Check crash logs for Btrfs mount or log-recovery panics.
  • Validate patched kernels in staging before production rollout.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-47145 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70a, e02119d5a7b4396c5a872582fddc8bd6d305a70aunaffected
LinuxLinux2.6.29, 0, 4.4.271, 4.9.271, 4.14.235, 4.19.193, 5.4.124, 5.10.42, 5.12.9, 5.13affected
Weakness

CWE details

No CWE listed

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