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CVE-2026-72123

can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.265, 5.15.216, 4.20, 5.5, 5.19, and 5 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

In the Linux kernel, the following vulnerability has been resolved: can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly synchronize_rcu()") replaced synchronize_rcu() in bcm_delete_rx_op() with call_rcu() and introduced the RX_NO_AUTOTIMER flag. However, this flag check was omitted for thrtimer in the packet rx fast-path. During BCM RX operation teardown, a concurrent RCU reader (bcm_rx_handler) can race and re-arm thrtimer via bcm_rx_update_and_send() after call_rcu() has been scheduled. Once the RCU grace period elapses, bcm_op is freed. The subsequently firing thrtimer then dereferences the deallocated op, causing a UAF. Adding flag checks to the rx fast-path (bcm_rx_update_and_send) does not fully close the TOCTOU race and introduces latency for every CAN frame. Conversely, calling hrtimer_cancel() directly inside the RCU callback (softirq context) is fatal as hrtimer_cancel() can sleep, triggering a "scheduling while atomic" panic. Resolve this by deferring the timer cancellation and memory free to a dedicated unbound workqueue (bcm_wq). The RCU callback now queues a work item to bcm_wq, which safely cancels both timers and deallocates memory in sleepable process context. A dedicated workqueue is used to prevent system-wide WQ saturation and is cleanly flushed/destroyed on module unload to avoid rmmod page faults. Since the deferred work can now outlive the calling context by an unbounded amount, also take a reference on op->sk when it is assigned and drop it only once the deferred work has cancelled both timers, so a socket can no longer be freed out from under a still-armed timer whose callback (bcm_send_to_user()) dereferences op->sk.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 85cd41070df992d3c0dfd828866fdd243d3b774a · fixed in de5fce46637de05bef56ec08528127676eb6fc9b; From f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 · fixed in 036a8c320ca11bc912e8027adcfad14b326f067e; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in 3cf4fd5316f449811d8baf1bc6978ef5a7b743a9; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in 4177762f70646ac48a2af382e45a795cbd295198; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in 6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in ce2d4b121fb7545e1ed588e860c8e5fd5ad45224; From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 · fixed in 68973f9db76144825e4f35dfdc80fb8279eb2d57; From 5.10.130 · fixed in 5.10.265; From 5.15.54 · fixed in 5.15.216; From 4.19.252 · fixed in 4.20; From 5.4.205 · fixed in 5.5; From 5.18.11 · fixed in 5.19

  • Linux Linux

    5.19

  • KernelLinux

    fixed in 5.10.265; From 5.11.0 · fixed in 5.15.216; From 5.16.0 · fixed in 6.1.178; From 5.19.0 · fixed in 6.6.145; From 6.2.0 · fixed in 6.12.97; From 6.7.0 · fixed in 6.18.40; From 6.13.0 · fixed in 7.1.5

References 8

git.kernel.org