examples/c: Fix ringbuf leaks in C libbpf examples

examples/c/bootstrap.bpf.c

@@ -45,6 +45,9 @@ int handle_exec(struct trace_event_raw_sched_process_exec *ctx)
 	if (!e)
 		return 0;
 
+	/* zero out buffer to avoid leaking prior record bytes */
+	__builtin_memset(e, 0, sizeof(*e));
+
 	/* fill out the sample with data */
 	task = (struct task_struct *)bpf_get_current_task();
 
@@ -95,6 +98,9 @@ int handle_exit(struct trace_event_raw_sched_process_template *ctx)
 	if (!e)
 		return 0;
 
+	/* zero out buffer to avoid leaking prior record bytes */
+	__builtin_memset(e, 0, sizeof(*e));
+
 	/* fill out the sample with data */
 	task = (struct task_struct *)bpf_get_current_task();
 

examples/c/profile.bpf.c

@@ -14,6 +14,13 @@ struct {
 	__uint(max_entries, 256 * 1024);
 } events SEC(".maps");
 
+/* zero out buffer (manual byte loop, struct is too big for inline memset) */
+static __noinline void zero_buf(void *p, __u64 sz)
+{
+	for (__u64 i = 0; i < sz; i++)
+		*(volatile char *)((char *)p + i) = 0;
+}
+
 SEC("perf_event")
 int profile(void *ctx)
 {
@@ -26,6 +33,10 @@ int profile(void *ctx)
 	if (!event)
 		return 1;
 
+	/* zero out buffer to avoid leaking prior record bytes (kstack/ustack
+	 * tail past *_sz is only partially written by bpf_get_stack) */
+	zero_buf(event, sizeof(*event));
+
 	event->pid = pid;
 	event->cpu_id = cpu_id;
 

examples/c/sockfilter.bpf.c

@@ -49,6 +49,10 @@ int socket_handler(struct __sk_buff *skb)
 	if (!e)
 		return 0;
 
+	/* zero out buffer to avoid leaking prior record bytes (the GRE
+	 * branch below skips writing src_addr/dst_addr) */
+	__builtin_memset(e, 0, sizeof(*e));
+
 	bpf_skb_load_bytes(skb, nhoff + offsetof(struct iphdr, protocol), &e->ip_proto, 1);
 
 	if (e->ip_proto != IPPROTO_GRE) {