{"id":"CVE-2026-72123","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-72123","summary":"can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ncan: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF\n\nCommit f1b4e32aca08 (\"can: bcm: use call_rcu() instead of costly\nsynchronize_rcu()\") replaced synchronize_rcu() in bcm_delete_rx_op()\nwith call_rcu() and introduced the RX_NO_AUTOTIMER flag.\n\nHowever, this flag check was omitted for thrtimer in the packet rx\nfast-path. During BCM RX operation teardown, a concurrent RCU reader\n(bcm_rx_handler) can race and re-arm thrtimer via\nbcm_rx_update_and_send() after call_rcu() has been scheduled.  Once\nthe RCU grace period elapses, bcm_op is freed.  The subsequently\nfiring thrtimer then dereferences the deallocated op, causing a UAF.\n\nAdding flag checks to the rx fast-path (bcm_rx_update_and_send) does not\nfully close the TOCTOU race and introduces latency for every CAN frame.\nConversely, calling hrtimer_cancel() directly inside the RCU callback\n(softirq context) is fatal as hrtimer_cancel() can sleep, triggering\na \"scheduling while atomic\" panic.\n\nResolve this by deferring the timer cancellation and memory free to a\ndedicated unbound workqueue (bcm_wq).  The RCU callback now queues a\nwork item to bcm_wq, which safely cancels both timers and deallocates\nmemory in sleepable process context.  A dedicated workqueue is used to\nprevent system-wide WQ saturation and is cleanly flushed/destroyed\non module unload to avoid rmmod page faults.\n\nSince the deferred work can now outlive the calling context by an\nunbounded amount, also take a reference on op->sk when it is assigned\nand drop it only once the deferred work has cancelled both timers, so a\nsocket can no longer be freed out from under a still-armed timer whose\ncallback (bcm_send_to_user()) dereferences op->sk.","published":"2026-08-15T05:53:01.433Z","modified":"2026-08-18T03:56:54.773319911Z","cvss":{"score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.1.178"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/3cf4fd5316f449811d8baf1bc6978ef5a7b743a9"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4177762f70646ac48a2af382e45a795cbd295198"},{"type":"WEB","url":"https://git.kernel.org/stable/c/68973f9db76144825e4f35dfdc80fb8279eb2d57"},{"type":"WEB","url":"https://git.kernel.org/stable/c/6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ce2d4b121fb7545e1ed588e860c8e5fd5ad45224"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72123.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72123"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-18T03:56:54.773319911Z"}}