{"id":"CVE-2026-99140","aliases":[],"title":"tracing: Fix hist trigger timestamps for buffered events","titleSource":"Linux","descriptionSource":"Linux","products":[{"vendor":"Linux","name":"Linux","platforms":[],"versions":[{"version":"b94bc80df64823e676b506f8de7dcf6a688d681e","status":"affected","lessThan":"09c7cce2e59e6b3b1807520bcb1980c561f15d1e","versionType":"git"},{"version":"b94bc80df64823e676b506f8de7dcf6a688d681e","status":"affected","lessThan":"89e90b16aadd6e66bd0323bc8dfc76a62e756b57","versionType":"git"},{"version":"b94bc80df64823e676b506f8de7dcf6a688d681e","status":"affected","lessThan":"9414ca3b99e5a7f1f3bf51c2a01b383e1b355dd0","versionType":"git"}],"defaultStatus":"unaffected","source":"Linux","url":"https://www.cve.org/CVERecord?id=CVE-2026-99140"},{"vendor":"Linux","name":"Linux","platforms":[],"versions":[{"version":"5.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.13","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"defaultStatus":"affected","source":"Linux","url":"https://www.cve.org/CVERecord?id=CVE-2026-99140"}],"remediation":[],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Fix hist trigger timestamps for buffered events\n\nSyzkaller triggered a WARN_ON_ONCE(!nest) warning:\n\n  WARNING: kernel/trace/ring_buffer.c:821 at ring_buffer_event_time_stamp\n  Call trace:\n    ring_buffer_event_time_stamp\n    hist_field_timestamp\n    hist_fn_call\n    event_hist_trigger\n    event_triggers_call\n    __event_trigger_test_discard\n    trace_event_buffer_commit\n    do_trace_event_raw_event_sched_switch\n    trace_event_raw_event_sched_switch\n\nThe warning is probabilistically reproducible and is related to syzkaller\nexecuting the following commands:\n\n  echo 'prev_pid == 999999' > events/sched/sched_switch/filter\n  echo 'hist:keys=common_timestamp' > events/sched/sched_switch/trigger\n\nThe specific triggering process is as follows:\n\nCPU 0                                           CPU 1\n(context switching)                             (echo 'hist:keys=common_timestamp' > \\\n                                                        events/sched/sched_switch/trigger)\ndo_trace_event_raw_event_##call\n  trace_event_buffer_lock_reserve\n    if (!tr->no_filter_buffering_ref &&\n        trace_file->flags & EVENT_FILE_FL_FILTERED)\n        return entry;  // return directly\n                                                event_hist_trigger_parse\n                                                  hist_register_trigger\n                                                    tracing_set_filter_buffering(file->tr, true);\n                                                      tr->no_filter_buffering_ref++;\n    __trace_buffer_lock_reserve\n      rb_start_commit\n        local_inc(&cpu_buffer->committing);  // skipped and not executed\n  trace_event_buffer_commit\n    __event_trigger_test_discard\n      event_triggers_call\n        event_hist_trigger\n          hist_fn_call\n            hist_field_timestamp\n              ring_buffer_event_time_stamp\n                nest = local_read(&cpu_buffer->committing);\n                WARN_ON_ONCE(!nest)  // trigger warning\n\nThe root cause is that when an event file has a filter attached and the\nhist trigger has not yet been attached, trace_event_buffer_lock_reserve()\nwrites the event into the per-CPU trace_buffered_event temp buffer instead\nof reserving it in the ring buffer, so cpu_buffer->committing is not\nincremented. When the event is later processed at commit time by a hist\ntrigger, hist_field_timestamp() -> ring_buffer_event_time_stamp() sees a\nzero committing count, triggering WARN_ON_ONCE(!nest).\n\ntracing_event_time_stamp() was added by commit d8279bfc5e959 (\"tracing:\nAdd tracing_event_time_stamp() API\") for exactly this case: if the event\nis the per-CPU trace_buffered_event, it returns the current ring buffer\ntimestamp. But it never gained a caller. Use it in hist_field_timestamp(),\nso that a hist trigger that races onto a buffered event records the\ncurrent time, which is only marginally later than when the event was\nrecorded, instead of warning and recording a bogus timestamp.","severity":"unknown","score":null,"published":"2026-10-28T10:34:51.421Z","modified":"2026-10-28T10:34:51.421Z","withdrawn":false,"knownExploited":false,"affected":[],"references":["https://git.kernel.org/stable/c/09c7cce2e59e6b3b1807520bcb1980c561f15d1e","https://git.kernel.org/stable/c/89e90b16aadd6e66bd0323bc8dfc76a62e756b57","https://git.kernel.org/stable/c/9414ca3b99e5a7f1f3bf51c2a01b383e1b355dd0"],"sources":[{"name":"CVE","id":"CVE-2026-99140","modified":"2026-10-28T10:34:51.421Z","url":"https://www.cve.org/CVERecord?id=CVE-2026-99140"}],"assessments":[],"sourceAffected":[],"kev":{"status":"not-listed","checkedAt":"2026-10-28T15:40:31.878Z"},"coverage":[{"source":"NVD","status":"not-checked"},{"source":"GHSA","status":"not-checked"},{"source":"EUVD","status":"not-checked"},{"source":"EPSS","status":"not-checked"}],"evidence":[]}