# CVE-2026-99173: eventfs: Free the eventfs_inode after an rcu grace period too


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** BELL-CVE-2026-99173, DEBIAN-CVE-2026-99173, GHSA-fx9f-7wc6-cjjx, UBUNTU-CVE-2026-99173

## What is CVE-2026-99173?

CVE-2026-99173 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

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

eventfs: Free the eventfs_inode after an rcu grace period too

tracefs_d_revalidate() reads ->is_freed of the eventfs_inode that
dentry->d_fsdata points to, and ->d_revalidate() is called in rcu
pathwalk mode with nothing but rcu_read_lock() held. The dentry itself
stays around for such a walker, but tracefs_d_release() drops its
reference to the eventfs_inode when the dentry is killed, and
release_ei() then frees it after a grace period of eventfs_srcu. An
SRCU grace period doesn't wait for rcu_read_lock() sections, so the
walker can read an eventfs_inode that is already gone.

With a pathwalk held up in tracefs_d_revalidate() while the dentry goes
away:

  BUG: KASAN: slab-use-after-free in tracefs_d_revalidate+0x76/0x90
  Read of size 1 at addr ff1100010152d8d0 by task walker/97
  Call Trace:
   <TASK>
   tracefs_d_revalidate+0x76/0x90
   lookup_fast+0x320/0x640
   path_lookupat+0x160/0xb00
   filename_lookup+0x1f1/0x5b0
   vfs_statx+0xd7/0x3b0
   vfs_fstatat+0x4d/0x90
   __do_sys_newfstatat+0xa0/0x100
   do_syscall_64+0x10e/0x5e0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  [...]
  Allocated by task 1:
   __kmalloc_cache_noprof+0x249/0x560
   eventfs_create_dir+0x7a/0x590
   event_create_dir+0x2fb/0xcf0
   trace_add_event_call+0xbf/0x150
  [...]
  Freed by task 11:
   kfree+0x1db/0x5b0
   srcu_invoke_callbacks+0x3a3/0x620
   process_one_work+0x937/0x1810
   worker_thread+0x4f1/0xd60

Before commit 8e556432477e ("eventfs: Use SRCU for freeing
eventfs_inodes") release_ei() used call_rcu(), which covered the walker,
while eventfs_iterate() needs the SRCU grace period. Wait for both and
chain call_rcu() from the SRCU callback.

## Which versions are affected by CVE-2026-99173?


## How do I fix CVE-2026-99173?

Upgrade to a fixed version.

## Is CVE-2026-99173 being exploited?

There is no known exploitation of CVE-2026-99173 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99173 and fix it if it is affected.

What it is: CVE-2026-99173 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99173 in the wild and no public exploit code.

Affected product: 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-2026-99173/ (Markdown: https://insights.sbomify.com/CVE-2026-99173/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99173
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99173
- OSV: https://osv.dev/vulnerability/CVE-2026-99173

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99173/
Summaries are generated and may contain mistakes; the official description above is the record.