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Fencer Vulns
medium 5.5

CVE-2021-47145 json

btrfs: do not BUG_ON in link_to_fixup_dir

published 2024-03-25 2 y ago modified 2026-06-17 4 mo ago also EUVD-2021-33793

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 19%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 4.4.271, 4.9.271, 4.14.235, 4.19.193, 5.4.124, 5.10.42, 5.12.9, 5.13
  • linux Debian 14, Debian 13, Debian 12 5.14.6-1

debian advisories DEBIAN-CVE-2021-47145

  • linux Ubuntu 18.04 LTS 4.15.0-151.157
  • linux Ubuntu 20.04 LTS 5.4.0-80.90
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1109.116
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1054.57
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1049.53
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1097.99
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1044.46
  • linux-azure Ubuntu 20.04 LTS 5.4.0-1055.57

ubuntu advisories UBUNTU-CVE-2021-47145

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-azure SLES for SAP 12 SP5, SLES 12 SP5 4.12.14-16.194.1
  • kernel-syms-azure SLES for SAP 12 SP5, SLES 12 SP5 4.12.14-16.194.1
  • kernel-source-azure SLES for SAP 12 SP5, SLES 12 SP5 4.12.14-16.194.1
  • kernel-syms SLES for SAP 12 SP5, SLES 12 SP5 4.12.14-122.222.1
  • kernel-source SLES for SAP 12 SP5, SLES 12 SP5 4.12.14-122.222.1
  • kernel-default SLES for SAP 12 SP5, SLES 12 SP5, SLE Workstation Extension 12 SP5 +2 more 4.12.14-122.222.1
  • kernel-obs-build SLE Software Development Kit 12 SP5 4.12.14-122.222.1
  • kernel-rt SLE Real Time 12 SP5 4.12.14-10.194.1

suse advisories SUSE-SU-2024:2901-1SUSE-SU-2024:2561-1SUSE-SU-2024:2493-1

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-2021-47145 updated cvss 5.5

kernel: btrfs: do not BUG_ON in link_to_fixup_dir

  • 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

0.27% chance of exploitation in the next 30 days, higher than 19% of all scored CVEs (FIRST EPSS, 2026-11-08).

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

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.