# CVE-2026-46052: ceph: only d_add() negative dentries when they are unhashed

> A flaw in the Linux kernel's Ceph filesystem allows a local attacker to cause a system hang via infinite loop in dentry lookup.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-88445, BELL-CVE-2026-46052, DEBIAN-CVE-2026-46052, GHSA-vjcv-x2xf-6m7h, ROOT-OS-DEBIAN-11-CVE-2026-46052, ROOT-OS-DEBIAN-12-CVE-2026-46052, ROOT-OS-UBUNTU-2204-CVE-2026-46052, ROOT-OS-UBUNTU-2404-CVE-2026-46052, UBUNTU-CVE-2026-46052

## What is CVE-2026-46052?

CVE-2026-46052 is a high-severity denial of service vulnerability in Linux kernel, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ceph: only d_add() negative dentries when they are unhashed

Ceph can call d_add(dentry, NULL) on a negative dentry that is already
present in the primary dcache hash.

In the current VFS that is not safe.  d_add() goes through __d_add()
to __d_rehash(), which unconditionally reinserts dentry->d_hash into
the hlist_bl bucket.  If the dentry is already hashed, reinserting the
same node can corrupt the bucket, including creating a self-loop.
Once that happens, __d_lookup() can spin forever in the hlist_bl walk,
typically looping only on the d_name.hash mismatch check and
eventually triggering RCU stall reports like this one:

 rcu: INFO: rcu_sched self-detected stall on CPU
 rcu:         87-....: (2100 ticks this GP) idle=3a4c/1/0x4000000000000000 softirq=25003319/25003319 fqs=829
 rcu:         (t=2101 jiffies g=79058445 q=698988 ncpus=192)
 CPU: 87 UID: 2952868916 PID: 3933303 Comm: php-cgi8.3 Not tainted 6.18.17-i1-amd #950 NONE
 Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.6 09/22/2023
 RIP: 0010:__d_lookup+0x46/0xb0
 Code: c1 e8 07 48 8d 04 c2 48 8b 00 49 89 fc 49 89 f5 48 89 c3 48 83 e3 fe 48 83 f8 01 77 0f eb 2d 0f 1f 44 00 00 48 8b 1b 48 85 db <74> 20 39 6b 18 75 f3 48 8d 7b 78 e8 ba 85 d0 00 4c 39 63 10 74 1f
 RSP: 0018:ff745a70c8253898 EFLAGS: 00000282
 RAX: ff26e470054cb208 RBX: ff26e470054cb208 RCX: 000000006e958966
 RDX: ff26e48267340000 RSI: ff745a70c82539b0 RDI: ff26e458f74655c0
 RBP: 000000006e958966 R08: 0000000000000180 R09: 9cd08d909b919a89
 R10: ff26e458f74655c0 R11: 0000000000000000 R12: ff26e458f74655c0
 R13: ff745a70c82539b0 R14: d0d0d0d0d0d0d0d0 R15: 2f2f2f2f2f2f2f2f
 FS:  00007f5770896980(0000) GS:ff26e482c5d88000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007f5764de50c0 CR3: 000000a72abb5001 CR4: 0000000000771ef0
 PKRU: 55555554
 Call Trace:
  <TASK>
  lookup_fast+0x9f/0x100
  walk_component+0x1f/0x150
  link_path_walk+0x20e/0x3d0
  path_lookupat+0x68/0x180
  filename_lookup+0xdc/0x1e0
  vfs_statx+0x6c/0x140
  vfs_fstatat+0x67/0xa0
  __do_sys_newfstatat+0x24/0x60
  do_syscall_64+0x6a/0x230
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

This is reachable with reused cached negative dentries.  A Ceph lookup
or atomic_open can be handed a negative dentry that is already hashed,
and fs/ceph/dir.c then hits one of two paths that incorrectly assume
"negative" also means "unhashed":

  - ceph_finish_lookup():
      MDS reply is -ENOENT with no trace
      -> d_add(dentry, NULL)

  - ceph_lookup():
      local ENOENT fast path for a complete directory with shared caps
      -> d_add(dentry, NULL)

Both paths can therefore re-add an already-hashed negative dentry.

Ceph already uses the correct pattern elsewhere: ceph_fill_trace() only
calls d_add(dn, NULL) for a negative null-dentry reply when d_unhashed(dn)
is true.

Fix both fs/ceph/dir.c sites the same way: only call d_add() for a
negative dentry when it is actually unhashed.  If the negative dentry
is already hashed, leave it in place and reuse it as-is.

This preserves the existing behavior for unhashed dentries while
avoiding d_hash list corruption for reused hashed negatives.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-46052?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-46052?

Apply the vendor's patch.

## Is CVE-2026-46052 being exploited?

There is no known exploitation of CVE-2026-46052 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46052 and fix it if it is affected.

What it is: CVE-2026-46052 is a high-severity denial of service vulnerability in Linux kernel, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-46052 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-46052/ (Markdown: https://insights.sbomify.com/CVE-2026-46052/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46052
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46052
- OSV: https://osv.dev/vulnerability/CVE-2026-46052

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46052/
Summaries are generated and may contain mistakes; the official description above is the record.