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CVE-2026-53264

net/sched: act_api: use RCU with deferred freeing for action lifecycle

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: poc
  • Automatable: no
  • Technical impact: total

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: poc · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux 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 Linux

    4.14

  • KernelLinux

    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

References 8

git.kernel.org