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Fencer Vulns
medium 5.5

CVE-2024-26727 json

btrfs: do not ASSERT() if the newly created subvolume already got read

published 2024-04-03 2 y ago modified 2026-06-17 4 mo ago also EUVD-2024-23989

cvss
5.5
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 13%
public exploits
0
none known

Summary

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

btrfs: do not ASSERT() if the newly created subvolume already got read

[BUG] There is a syzbot crash, triggered by the ASSERT() during subvolume creation:

assertion failed: !anon_dev, in fs/btrfs/disk-io.c:1319 ------------[ cut here ]------------ kernel BUG at fs/btrfs/disk-io.c:1319! invalid opcode: 0000 [#1] PREEMPT SMP KASAN RIP: 0010:btrfs_get_root_ref.part.0+0x9aa/0xa60 <TASK> btrfs_get_new_fs_root+0xd3/0xf0 create_subvol+0xd02/0x1650 btrfs_mksubvol+0xe95/0x12b0 __btrfs_ioctl_snap_create+0x2f9/0x4f0 btrfs_ioctl_snap_create+0x16b/0x200 btrfs_ioctl+0x35f0/0x5cf0 __x64_sys_ioctl+0x19d/0x210 do_syscall_64+0x3f/0xe0 entry_SYSCALL_64_after_hwframe+0x63/0x6b ---[ end trace 0000000000000000 ]---

[CAUSE] During create_subvol(), after inserting root item for the newly created subvolume, we would trigger btrfs_get_new_fs_root() to get the btrfs_root of that subvolume.

The idea here is, we have preallocated an anonymous device number for the subvolume, thus we can assign it to the new subvolume.

But there is really nothing preventing things like backref walk to read the new subvolume. If that happens before we call btrfs_get_new_fs_root(), the subvolume would be read out, with a new anonymous device number assigned already.

In that case, we would trigger ASSERT(), as we really expect no one to read out that subvolume (which is not yet accessible from the fs). But things like backref walk is still possible to trigger the read on the subvolume.

Thus our assumption on the ASSERT() is not correct in the first place.

[FIX] Fix it by removing the ASSERT(), and just free the @anon_dev, reset it to 0, and continue.

If the subvolume tree is read out by something else, it should have already get a new anon_dev assigned thus we only need to free the preallocated one.

Patch / fix

  • Linux Linux 5.9, 5.10.210, 5.15.149, 6.1.79, 6.6.18, 6.7.6, 6.8
  • linux Debian 12 6.1.82-1
  • linux Debian 14, Debian 13 6.7.7-1

debian advisories DEBIAN-CVE-2024-26727

  • linux Ubuntu 22.04 LTS 5.15.0-102.112
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1057.63
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1055.63
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1054.59
  • linux-ibm Ubuntu 22.04 LTS 5.15.0-1050.53
  • linux-kvm Ubuntu 22.04 LTS 5.15.0-1054.59
  • linux-azure Ubuntu 22.04 LTS 5.15.0-1060.69
  • linux-gkeop Ubuntu 22.04 LTS 5.15.0-1040.46

ubuntu advisories UBUNTU-CVE-2024-26727

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-rt SLE Micro 5.5, Real Time Module 15 SP5, openSUSE Leap 15.5 5.14.21-150500.13.52.1
  • kernel-syms-rt Real Time Module 15 SP5, openSUSE Leap 15.5 5.14.21-150500.13.52.1
  • kernel-rt_debug Real Time Module 15 SP5, openSUSE Leap 15.5 5.14.21-150500.13.52.1
  • kernel-source-rt SLE Micro 5.5, Real Time Module 15 SP5, openSUSE Leap 15.5 5.14.21-150500.13.52.1
  • dtb-aarch64 openSUSE Leap 15.5 5.14.21-150500.55.62.1
  • kernel-64kb SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.62.2
  • kernel-syms SLE Module for Development Tools 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.62.1
  • kernel-obs-qa openSUSE Leap 15.5 5.14.21-150500.55.62.1

suse advisories SUSE-SU-2024:1663-1SUSE-SU-2024:1659-1SUSE-SU-2024:1647-1SUSE-SU-2024:1641-1SUSE-SU-2024:1490-1

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-2024-26727 updated cvss 5.5

kernel: btrfs: do not ASSERT() if the newly created subvolume already got read

  • 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 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

0.23% chance of exploitation in the next 30 days, higher than 13% 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

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.