From bbb68468641547d56c83012670bcaf77f3dacd64 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Fri, 16 Mar 2018 12:51:40 +0000 Subject: [PATCH] perf/core: Clear sibling list of detached events When perf_group_dettach() is called on a group leader, it updates each sibling's group_leader field to point to that sibling, effectively upgrading each siblnig to a group leader. After perf_group_detach has completed, the caller may free the leader event. We only remove siblings from the group leader's sibling_list when the leader has a non-empty group_node. This was fine prior to commit: 8343aae66167df67 ("perf/core: Remove perf_event::group_entry") ... as the sibling's sibling_list would be empty. However, now that we use the sibling_list field as both the list head and the list entry, this leaves each sibling with a non-empty sibling list, including the stale leader event. If perf_group_detach() is subsequently called on a sibling, it will appear to be a group leader, and we'll walk the sibling_list, potentially dereferencing these stale events. In 0day testing, this has been observed to result in kernel panics. Let's avoid this by always removing siblings from the sibling list when we promote them to leaders. Fixes: 8343aae66167df67 ("perf/core: Remove perf_event::group_entry") Signed-off-by: Mark Rutland Signed-off-by: Thomas Gleixner Cc: vincent.weaver@maine.edu Cc: Peter Zijlstra Cc: torvalds@linux-foundation.org Cc: Alexey Budankov Cc: valery.cherepennikov@intel.com Cc: linux-tip-commits@vger.kernel.org Cc: eranian@google.com Cc: acme@redhat.com Cc: alexander.shishkin@linux.intel.com Cc: davidcc@google.com Cc: kan.liang@intel.com Cc: Dmitry.Prohorov@intel.com Cc: Jiri Olsa Link: https://lkml.kernel.org/r/20180316131741.3svgr64yibc6vsid@lakrids.cambridge.arm.com --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 4d7a460d6669..2776a660db15 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1906,12 +1906,12 @@ static void perf_group_detach(struct perf_event *event) list_for_each_entry_safe(sibling, tmp, &event->sibling_list, sibling_list) { sibling->group_leader = sibling; + list_del_init(&sibling->sibling_list); /* Inherit group flags from the previous leader */ sibling->group_caps = event->group_caps; if (!RB_EMPTY_NODE(&event->group_node)) { - list_del_init(&sibling->sibling_list); add_event_to_groups(sibling, event->ctx); if (sibling->state == PERF_EVENT_STATE_ACTIVE) {