{"id":"CVE-2026-98861","title":"fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()","summary":"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 grac…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 56b4cfcf1518245493c60fd39c56978f508f1816 < a85d0f00671b4d4527317c10ba018680f7d8d673","Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < dd4a0d4993633b45470abf6da4ea0ca563402245","Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < e0a6249190402a28f1e2925a81acf573157d55ef","Linux a4f6a9005ed6cfd360ef2520430927f05f92ffb0","Linux >= 6.18.34 < 6.18.56","Linux >= 7.0.11 < 7.1","Linux 7.1"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:51:22.271Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98861","references":[{"url":"https://git.kernel.org/stable/c/a85d0f00671b4d4527317c10ba018680f7d8d673"},{"url":"https://git.kernel.org/stable/c/dd4a0d4993633b45470abf6da4ea0ca563402245"},{"url":"https://git.kernel.org/stable/c/e0a6249190402a28f1e2925a81acf573157d55ef"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T16:47:32.459Z","slug":"CVE-2026-98861","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= 56b4cfcf1518245493c60fd39c56978f508f1816 < a85d0f00671b4d4527317c10ba018680f7d8d673`\n- `Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < dd4a0d4993633b45470abf6da4ea0ca563402245`\n- `Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < e0a6249190402a28f1e2925a81acf573157d55ef`\n- `Linux a4f6a9005ed6cfd360ef2520430927f05f92ffb0`\n- `Linux >= 6.18.34 < 6.18.56`\n- `Linux >= 7.0.11 < 7.1`\n- `Linux 7.1`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}