# CVE-2024-26644: btrfs: don't abort filesystem when attempting to snapshot deleted subvolume

> A local attacker can cause a filesystem abort and denial of service by attempting to snapshot a deleted subvolume in the Linux kernel btrfs module.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Mar 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-26644, DEBIAN-CVE-2024-26644, GHSA-xr82-8hm6-h468, UBUNTU-CVE-2024-26644

## What is CVE-2024-26644?

CVE-2024-26644 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 26 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

btrfs: don't abort filesystem when attempting to snapshot deleted subvolume

If the source file descriptor to the snapshot ioctl refers to a deleted
subvolume, we get the following abort:

  BTRFS: Transaction aborted (error -2)
  WARNING: CPU: 0 PID: 833 at fs/btrfs/transaction.c:1875 create_pending_snapshot+0x1040/0x1190 [btrfs]
  Modules linked in: pata_acpi btrfs ata_piix libata scsi_mod virtio_net blake2b_generic xor net_failover virtio_rng failover scsi_common rng_core raid6_pq libcrc32c
  CPU: 0 PID: 833 Comm: t_snapshot_dele Not tainted 6.7.0-rc6 #2
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
  RIP: 0010:create_pending_snapshot+0x1040/0x1190 [btrfs]
  RSP: 0018:ffffa09c01337af8 EFLAGS: 00010282
  RAX: 0000000000000000 RBX: ffff9982053e7c78 RCX: 0000000000000027
  RDX: ffff99827dc20848 RSI: 0000000000000001 RDI: ffff99827dc20840
  RBP: ffffa09c01337c00 R08: 0000000000000000 R09: ffffa09c01337998
  R10: 0000000000000003 R11: ffffffffb96da248 R12: fffffffffffffffe
  R13: ffff99820535bb28 R14: ffff99820b7bd000 R15: ffff99820381ea80
  FS:  00007fe20aadabc0(0000) GS:ffff99827dc00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000559a120b502f CR3: 00000000055b6000 CR4: 00000000000006f0
  Call Trace:
   <TASK>
   ? create_pending_snapshot+0x1040/0x1190 [btrfs]
   ? __warn+0x81/0x130
   ? create_pending_snapshot+0x1040/0x1190 [btrfs]
   ? report_bug+0x171/0x1a0
   ? handle_bug+0x3a/0x70
   ? exc_invalid_op+0x17/0x70
   ? asm_exc_invalid_op+0x1a/0x20
   ? create_pending_snapshot+0x1040/0x1190 [btrfs]
   ? create_pending_snapshot+0x1040/0x1190 [btrfs]
   create_pending_snapshots+0x92/0xc0 [btrfs]
   btrfs_commit_transaction+0x66b/0xf40 [btrfs]
   btrfs_mksubvol+0x301/0x4d0 [btrfs]
   btrfs_mksnapshot+0x80/0xb0 [btrfs]
   __btrfs_ioctl_snap_create+0x1c2/0x1d0 [btrfs]
   btrfs_ioctl_snap_create_v2+0xc4/0x150 [btrfs]
   btrfs_ioctl+0x8a6/0x2650 [btrfs]
   ? kmem_cache_free+0x22/0x340
   ? do_sys_openat2+0x97/0xe0
   __x64_sys_ioctl+0x97/0xd0
   do_syscall_64+0x46/0xf0
   entry_SYSCALL_64_after_hwframe+0x6e/0x76
  RIP: 0033:0x7fe20abe83af
  RSP: 002b:00007ffe6eff1360 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
  RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007fe20abe83af
  RDX: 00007ffe6eff23c0 RSI: 0000000050009417 RDI: 0000000000000003
  RBP: 0000000000000003 R08: 0000000000000000 R09: 00007fe20ad16cd0
  R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
  R13: 00007ffe6eff13c0 R14: 00007fe20ad45000 R15: 0000559a120b6d58
   </TASK>
  ---[ end trace 0000000000000000 ]---
  BTRFS: error (device vdc: state A) in create_pending_snapshot:1875: errno=-2 No such entry
  BTRFS info (device vdc: state EA): forced readonly
  BTRFS warning (device vdc: state EA): Skipping commit of aborted transaction.
  BTRFS: error (device vdc: state EA) in cleanup_transaction:2055: errno=-2 No such entry

This happens because create_pending_snapshot() initializes the new root
item as a copy of the source root item. This includes the refs field,
which is 0 for a deleted subvolume. The call to btrfs_insert_root()
therefore inserts a root with refs == 0. btrfs_get_new_fs_root() then
finds the root and returns -ENOENT if refs == 0, which causes
create_pending_snapshot() to abort.

Fix it by checking the source root's refs before attempting the
snapshot, but after locking subvol_sem to avoid racing with deletion.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2024-26644?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2024-26644?

Apply the vendor's patch.

## Is CVE-2024-26644 being exploited?

There is no known exploitation of CVE-2024-26644 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-26644 and fix it if it is affected.

What it is: CVE-2024-26644 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 26 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-26644 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-26644/ (Markdown: https://insights.sbomify.com/CVE-2024-26644/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26644
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26644
- OSV: https://osv.dev/vulnerability/CVE-2024-26644

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26644/
Summaries are generated and may contain mistakes; the official description above is the record.