{"id":"CVE-2026-98530","summary":"kprobes: Fix permanent hang when flushing the kprobe optimizer","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nkprobes: Fix permanent hang when flushing the kprobe optimizer\n\nWriting 0 to /proc/sys/debug/kprobes-optimization while a kprobe is\njump-optimized never returns. The writer sleeps in D state forever with\nkprobe_sysctl_mutex held, so any later read or write of that sysctl\nhangs as well. For example, with vfs_read+9 as an optimizable address\nin this build:\n\n  # cd /sys/kernel/tracing\n  # echo 'p:myprobe vfs_read+9' \u003e\u003e kprobe_events\n  # echo 1 \u003e events/kprobes/myprobe/enable\n  # # wait until /sys/kernel/debug/kprobes/list shows [OPTIMIZED]\n  # echo 0 \u003e /proc/sys/debug/kprobes-optimization\n\n  INFO: task sh:246 blocked for more than 10 seconds.\n  Call Trace:\n   \u003cTASK\u003e\n   __schedule+0x1176/0x4f70\n   schedule+0xdc/0x2c0\n   schedule_timeout+0x17b/0x260\n   wait_for_completion+0x173/0x3c0\n   wait_for_kprobe_optimizer_locked+0xbc/0x130\n   proc_kprobes_optimization_handler+0x156/0x1b0\n   proc_sys_call_handler+0x324/0x490\n   vfs_write+0x52d/0xfe0\n   ksys_write+0xff/0x200\n   do_syscall_64+0x106/0x630\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n   \u003c/TASK\u003e\n  ...\n  INFO: task cat:265 is blocked on a mutex likely owned by task sh:246.\n\nwait_for_kprobe_optimizer_locked() reinitializes optimizer_completion,\nasks the optimizer thread to flush and sleeps in wait_for_completion().\nThe thread drains the (un)optimizing lists, but calls complete() only\nif completion_done() is true, i.e. if the completion is already done,\nwhich never happens while someone waits. disarm_all_kprobes() and\nkprobe_trace_self_tests_init() wait the same way.\n\nCalling complete() unconditionally would not be enough: the waiter\ndrops kprobe_mutex while it sleeps, and nothing else serializes the\nsysctl handler against the debugfs \"enabled\" file. A second flusher\nthat still finds the lists non-empty, e.g. because a disabled probe is\nqueued for unoptimizing, reinitializes the completion under the first:\n\n  sysctl write                      debugfs \"enabled\" write\n  unoptimize_all_kprobes()\n    wait_for_kprobe_optimizer_locked()\n      init_completion(c)\n      mutex_unlock(&kprobe_mutex)\n      wait_for_completion(c)\n                                    disarm_all_kprobes()\n                                      wait_for_kprobe_optimizer_locked()\n                                        init_completion(c)\n                                          // c-\u003ewait is reset, the first\n                                          // waiter is off the queue\n                                        mutex_unlock(&kprobe_mutex)\n                                        wait_for_completion(c)\n  kprobe_optimizer()\n    complete(c)\n      // wakes the debugfs writer only\n\nwhere c is &optimizer_completion. Lining up the two writes during an\noptimizer pass loses the sysctl writer this way.\n\nReplace the completion with a counter of optimizer passes, bumped at the\nend of each pass and signalled with wake_up_var_locked(), both under\nkprobe_mutex. A flusher samples the count and waits with\nwait_var_event_mutex(), which drops kprobe_mutex only while sleeping, so\na new count means a whole pass ran in the meantime. Nothing is\nreinitialized, so several flushers can sleep in the wait at once.","modified":"2026-10-20T02:30:24.130739105Z","published":"2026-10-18T15:17:48.670Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98530.json","cna_assigner":"Linux"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5bfa9f1a9dcb6ecb607adbc1c0226605c972935b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f05a01fc7d4f731b4c100d2aef1e85ad77728862"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98530.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98530"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"73c12f209462d1712c5f55f3021a1b65b2e084c3"},{"fixed":"f05a01fc7d4f731b4c100d2aef1e85ad77728862"},{"fixed":"5bfa9f1a9dcb6ecb607adbc1c0226605c972935b"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98530.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.0.0"},{"fixed":"7.2.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98530.json"}}],"schema_version":"1.9.0"}