{"id":"AZL-111266","summary":"CVE-2026-99140 affecting package kernel 6.6.157.1-1","details":"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' \u003e events/sched/sched_switch/filter\n  echo 'hist:keys=common_timestamp' \u003e 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' \u003e \\\n                                                        events/sched/sched_switch/trigger)\ndo_trace_event_raw_event_##call\n  trace_event_buffer_lock_reserve\n    if (!tr-\u003eno_filter_buffering_ref &&\n        trace_file-\u003eflags & EVENT_FILE_FL_FILTERED)\n        return entry;  // return directly\n                                                event_hist_trigger_parse\n                                                  hist_register_trigger\n                                                    tracing_set_filter_buffering(file-\u003etr, true);\n                                                      tr-\u003eno_filter_buffering_ref++;\n    __trace_buffer_lock_reserve\n      rb_start_commit\n        local_inc(&cpu_buffer-\u003ecommitting);  // 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-\u003ecommitting);\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-\u003ecommitting is not\nincremented. When the event is later processed at commit time by a hist\ntrigger, hist_field_timestamp() -\u003e 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.","modified":"2026-10-30T05:35:37Z","published":"2026-10-28T11:17:33Z","upstream":["CVE-2026-99140"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99140"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-111266.json"}}],"schema_version":"1.9.2"}