CVE-2024-26727btrfs: do not ASSERT() if the newly created subvolume already got read

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.

Timeline

Scores

EPSS (exploitation in 30 days)

0.23% · top 86% of all CVEs (13 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Affected products

• Linux · Linux

  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < 3f5d47eb163bceb1b9e613c9003bae5fefc0046f
  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < e31546b0f34af21738c4ceac47d662c00ee6382f
  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < 66b317a2fc45b2ef66527ee3f8fa08fb5beab88d
  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < 833775656d447c545133a744a0ed1e189ce61430
  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < 5a172344bfdabb46458e03708735d7b1a918c468
  • affected 2dfb1e43f57dd3aeaa66f7cf05d068db2d4c8788 – < e03ee2fe873eb68c1f9ba5112fee70303ebf9dfb
  • affected 917d608fe375041eb7f29befa6a6d7fd3cf32dde
  • affected 5.8.3 – < 5.9

• Linux · Linux

  • affected 5.9
  • unaffected < 5.9
  • unaffected 5.10.210 – ≤ 5.10.*
  • unaffected 5.15.149 – ≤ 5.15.*
  • unaffected 6.1.79 – ≤ 6.1.*
  • unaffected 6.6.18 – ≤ 6.6.*
  • unaffected 6.7.6 – ≤ 6.7.*
  • unaffected 6.8 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2024-23989 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2024-26727](https://cveledger.app/badge/CVE-2024-26727.svg)](https://cveledger.app/cve/CVE-2024-26727)

Record last updated 23 May 2026, 15:37 UTC.