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authorPeter Zijlstra <peterz@infradead.org>2016-08-04 14:37:24 +0200
committerIngo Molnar <mingo@kernel.org>2016-08-10 13:05:51 +0200
commit0b8f1e2e26bfc6b9abe3f0f3faba2cb0eecb9fb9 (patch)
tree5f645289667742567e9a76696a435b48b2db55c5 /kernel/events/core.c
parent69766c40c35de3a2c1142c43baa9951dfe11f002 (diff)
perf/core: Fix sideband list-iteration vs. event ordering NULL pointer deference crash
Vegard Nossum reported that perf fuzzing generates a NULL pointer dereference crash: > Digging a bit deeper into this, it seems the event itself is getting > created by perf_event_open() and it gets added to the pmu_event_list > through: > > perf_event_open() > - perf_event_alloc() > - account_event() > - account_pmu_sb_event() > - attach_sb_event() > > so at this point the event is being attached but its ->ctx is still > NULL. It seems like ->ctx is set just a bit later in > perf_event_open(), though. > > But before that, __schedule() comes along and creates a stack trace > similar to the one above: > > __schedule() > - __perf_event_task_sched_out() > - perf_iterate_sb() > - perf_iterate_sb_cpu() > - event_filter_match() > - perf_cgroup_match() > - __get_cpu_context() > - (dereference ctx which is NULL) > > So I guess the question is... should the event be attached (= put on > the list) before ->ctx gets set? Or should the cgroup code check for a > NULL ->ctx? The latter seems like the simplest solution. Moving the list-add later creates a bit of a mess. Reported-by: Vegard Nossum <vegard.nossum@gmail.com> Tested-by: Vegard Nossum <vegard.nossum@gmail.com> Tested-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: David Carrillo-Cisneros <davidcc@google.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Kan Liang <kan.liang@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: f2fb6bef9251 ("perf/core: Optimize side-band event delivery") Link: http://lkml.kernel.org/r/20160804123724.GN6862@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/events/core.c')
-rw-r--r--kernel/events/core.c23
1 files changed, 18 insertions, 5 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a19550d80ab1..87d02b8cb87e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1716,8 +1716,8 @@ static inline int pmu_filter_match(struct perf_event *event)
static inline int
event_filter_match(struct perf_event *event)
{
- return (event->cpu == -1 || event->cpu == smp_processor_id())
- && perf_cgroup_match(event) && pmu_filter_match(event);
+ return (event->cpu == -1 || event->cpu == smp_processor_id()) &&
+ perf_cgroup_match(event) && pmu_filter_match(event);
}
static void
@@ -1737,8 +1737,8 @@ event_sched_out(struct perf_event *event,
* maintained, otherwise bogus information is return
* via read() for time_enabled, time_running:
*/
- if (event->state == PERF_EVENT_STATE_INACTIVE
- && !event_filter_match(event)) {
+ if (event->state == PERF_EVENT_STATE_INACTIVE &&
+ !event_filter_match(event)) {
delta = tstamp - event->tstamp_stopped;
event->tstamp_running += delta;
event->tstamp_stopped = tstamp;
@@ -2236,10 +2236,15 @@ perf_install_in_context(struct perf_event_context *ctx,
lockdep_assert_held(&ctx->mutex);
- event->ctx = ctx;
if (event->cpu != -1)
event->cpu = cpu;
+ /*
+ * Ensures that if we can observe event->ctx, both the event and ctx
+ * will be 'complete'. See perf_iterate_sb_cpu().
+ */
+ smp_store_release(&event->ctx, ctx);
+
if (!task) {
cpu_function_call(cpu, __perf_install_in_context, event);
return;
@@ -5969,6 +5974,14 @@ static void perf_iterate_sb_cpu(perf_iterate_f output, void *data)
struct perf_event *event;
list_for_each_entry_rcu(event, &pel->list, sb_list) {
+ /*
+ * Skip events that are not fully formed yet; ensure that
+ * if we observe event->ctx, both event and ctx will be
+ * complete enough. See perf_install_in_context().
+ */
+ if (!smp_load_acquire(&event->ctx))
+ continue;
+
if (event->state < PERF_EVENT_STATE_INACTIVE)
continue;
if (!event_filter_match(event))