{"id":"CVE-2026-98861","summary":"fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nfprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()\n\nunregister_fprobe() and unregister_fprobe_async() (used by BPF\nkprobe-multi) rely on standard RCU grace periods (synchronize_rcu()\nand call_rcu()) to wait until in-flight fprobe handlers complete before\nfreeing the fprobe.\n\nHowever, if an fprobe handler executes while RCU is not watching (such\nas in the idle loop or nohz_full extended quiescent states), standard\nRCU does not track preemption-disabled sections. Consequently,\nsynchronize_rcu() does not wait for those executions, which can lead\nto a use-after-free if the fprobe is freed immediately after\nunregistration. Ensure handlers exit early when !rcu_is_watching().\n\nFurthermore, fprobe_fgraph_entry() and fprobe_ftrace_entry() previously\nused guard(rcu)() and rcu_read_lock(), which invoke lockdep on every\nhit under CONFIG_PROVE_LOCKING. This adds overhead and can cause lockdep\nrecursion if probed functions interact with lockdep.\n\nSince rhltable_lookup() and rhl_for_each_entry_rcu() use\nrcu_dereference_all_check() (which checks rcu_read_lock_any_held()),\nholding preemption disabled via rcu_read_lock_sched_notrace() is fully\nvalid and sufficient so long as rcu_is_watching() is true.\n\nDefine and use guard(rcu_sched_notrace)() across fprobe_ftrace_entry(),\nfprobe_fgraph_entry(), and fprobe_return(). This eliminates fast-path\nrcu_read_lock() and lockdep overhead while guaranteeing safe grace\nperiod synchronization.","modified":"2026-10-19T02:47:37.120469720Z","published":"2026-10-18T15:51:22.271Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98861.json"},"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/a85d0f00671b4d4527317c10ba018680f7d8d673"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dd4a0d4993633b45470abf6da4ea0ca563402245"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e0a6249190402a28f1e2925a81acf573157d55ef"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98861.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98861"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"56b4cfcf1518245493c60fd39c56978f508f1816"},{"fixed":"a85d0f00671b4d4527317c10ba018680f7d8d673"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"657b594b2084b39a4bc6d8493aa2140cb00cea49"},{"fixed":"dd4a0d4993633b45470abf6da4ea0ca563402245"},{"fixed":"e0a6249190402a28f1e2925a81acf573157d55ef"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.18.34"},{"fixed":"6.18.56"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"7.0.11"},{"fixed":"7.1"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"a4f6a9005ed6cfd360ef2520430927f05f92ffb0"}]}],"versions":["v6.18.55","v6.18.54","v6.18.53","v6.18.52","v6.18.51","v6.18.50","v6.18.49","v6.18.48","v6.18.47","v6.18.46","v6.18.45","v6.18.44","v6.18.43","v6.18.42","v6.18.41","v6.18.40","v6.18.39","v6.18.38","v6.18.37","v6.18.36","v6.18.35","v6.18.34","v7.0.14","v7.0.13","v7.0.12","v7.0.11"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98861.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.18.56"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98861.json"}}],"schema_version":"1.9.0"}