[PATCH 2/2] perf: Add checks to prevent null ptr access

[Vinay Belgaumkar <vinay.belgaumkar@intel.com>]

Sashiko recommended some additional checks to prevent null pointer
access. Check for revoked states inside perf_event_read_local(), as
the pmu event may have already been freed at this point. Add a null
check inside __perf_event_read_cpu() as well before accessing the pmu
ptr.

Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
---
 kernel/events/core.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7777e82aad5e..059f82f0cadd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4788,14 +4788,19 @@ static inline const struct cpumask *perf_scope_cpu_topology_cpumask(unsigned int
 
 static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
 {
+	struct pmu *pmu = READ_ONCE(event->pmu);
 	int local_cpu = smp_processor_id();
 	u16 local_pkg, event_pkg;
 
 	if ((unsigned)event_cpu >= nr_cpu_ids)
 		return event_cpu;
 
+	if (!pmu)
+		return -ENODEV;
+
 	if (event->group_caps & PERF_EV_CAP_READ_SCOPE) {
-		const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(event->pmu->scope, event_cpu);
+		const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(pmu->scope,
+										event_cpu);
 
 		if (cpumask && cpumask_test_cpu(local_cpu, cpumask))
 			return local_cpu;
@@ -4917,6 +4922,11 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
 		goto out;
 	}
 
+	if (READ_ONCE(event->state) <= PERF_EVENT_STATE_REVOKED) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	/*
 	 * Get the event CPU numbers, and adjust them to local if the event is
 	 * a per-package event that can be read locally
-- 
2.38.1