---
id: "CVE-2026-99173"
kind: "vulnerability"
aliases: ["CVE-2026-99173"]
title: "Linux kernel tracefs: use-after-free in eventfs revalidation during dentry release"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["linux-kernel", "other", "self-hosted", "tracing"]
not_affected_if: ["tracefs-not-mounted"]
published_at: "2026-10-28T11:17:37+00:00"
first_seen_at: "2026-10-28T11:32:36+00:00"
updated_at: "2026-10-28T11:35:34+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99173", "first_seen_at": "2026-10-28T11:32:36+00:00"}]
---

# Linux kernel tracefs: use-after-free in eventfs revalidation during dentry release

In the Linux kernel's tracefs/eventfs code, a path lookup running under RCU can read an eventfs_inode that was already freed when its dentry is torn down. The sources describe a KASAN slab-use-after-free, which can crash the kernel or let a local user read freed memory.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare the running kernel against the fixed kernel versions in the stable tree (unknown: the sources do not list them)
- Check whether tracefs is mounted with `mount | grep tracefs` (unknown: the sources do not say this is the only trigger)

## Fix

- Update the Linux kernel to a release that contains the upstream eventfs fix (unknown: the sources do not name the fixed version)
- Reboot into the patched kernel after updating

## Timeline

- 2026-10-28T11:32:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99173

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_