perf: Fix racy group access

While looking at some fuzzer output I noticed that we do not hold any
locks on leader->ctx and therefore the sibling_list iteration is
unsafe.

Acquire the relevant ctx->mutex before calling into the pmu specific
code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Link: http://lkml.kernel.org/r/20150225151639.GL5029@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index b01dfb602db15222d9be368eca166fc2d2e3a27d..bb1a7c36e7941d38c542449c467862effc6a282f 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7036,12 +7036,23 @@ EXPORT_SYMBOL_GPL(perf_pmu_unregister);
 
 static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
 {
+       struct perf_event_context *ctx = NULL;
        int ret;
 
        if (!try_module_get(pmu->module))
                return -ENODEV;
+
+       if (event->group_leader != event) {
+               ctx = perf_event_ctx_lock(event->group_leader);
+               BUG_ON(!ctx);
+       }
+
        event->pmu = pmu;
        ret = pmu->event_init(event);
+
+       if (ctx)
+               perf_event_ctx_unlock(event->group_leader, ctx);
+
        if (ret)
                module_put(pmu->module);