CVE-2024-26727

CVE-2024-26727 is a medium-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-617.

Key facts

Description

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.

Frequently asked questions

What is CVE-2024-26727?
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.
How severe is CVE-2024-26727?
CVE-2024-26727 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2024-26727 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2024-26727?
CVE-2024-26727 primarily affects Linux Linux Kernel. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2024-26727?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2024-26727 have an EU (EUVD) identifier?
Yes. CVE-2024-26727 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2024-23989.
When was CVE-2024-26727 published?
CVE-2024-26727 was published on 2024-04-03 and last updated on 2026-06-17.

References

Affected products (5)

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