samples, selftests/bpf: add NULL check for ksym_search

Since, ksym_search added with verification logic for symbols existence,
it could return NULL when the kernel symbols are not loaded.

This commit will add NULL check logic after ksym_search.
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

samples/bpf/offwaketime_user.c

@@ -28,6 +28,11 @@ static void print_ksym(__u64 addr)
 	if (!addr)
 		return;
 	sym = ksym_search(addr);
+	if (!sym) {
+		printf("ksym not found. Is kallsyms loaded?\n");
+		return;
+	}
+
 	if (PRINT_RAW_ADDR)
 		printf("%s/%llx;", sym->name, addr);
 	else

samples/bpf/sampleip_user.c

@@ -109,6 +109,11 @@ static void print_ip_map(int fd)
 	for (i = 0; i < max; i++) {
 		if (counts[i].ip > PAGE_OFFSET) {
 			sym = ksym_search(counts[i].ip);
+			if (!sym) {
+				printf("ksym not found. Is kallsyms loaded?\n");
+				continue;
+			}
+
 			printf("0x%-17llx %-32s %u\n", counts[i].ip, sym->name,
 			       counts[i].count);
 		} else {

samples/bpf/spintest_user.c

@@ -37,8 +37,13 @@ int main(int ac, char **argv)
 			bpf_map_lookup_elem(map_fd[0], &next_key, &value);
 			assert(next_key == value);
 			sym = ksym_search(value);
-			printf(" %s", sym->name);
 			key = next_key;
+			if (!sym) {
+				printf("ksym not found. Is kallsyms loaded?\n");
+				continue;
+			}
+
+			printf(" %s", sym->name);
 		}
 		if (key)
 			printf("\n");

samples/bpf/trace_event_user.c

@@ -34,6 +34,11 @@ static void print_ksym(__u64 addr)
 	if (!addr)
 		return;
 	sym = ksym_search(addr);
+	if (!sym) {
+		printf("ksym not found. Is kallsyms loaded?\n");
+		return;
+	}
+
 	printf("%s;", sym->name);
 	if (!strcmp(sym->name, "sys_read"))
 		sys_read_seen = true;

tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c

@@ -39,7 +39,7 @@ static int get_stack_print_output(void *data, int size)
 		} else {
 			for (i = 0; i < num_stack; i++) {
 				ks = ksym_search(raw_data[i]);
-				if (strcmp(ks->name, nonjit_func) == 0) {
+				if (ks && (strcmp(ks->name, nonjit_func) == 0)) {
 					found = true;
 					break;
 				}
@@ -56,7 +56,7 @@ static int get_stack_print_output(void *data, int size)
 		} else {
 			for (i = 0; i < num_stack; i++) {
 				ks = ksym_search(e->kern_stack[i]);
-				if (strcmp(ks->name, nonjit_func) == 0) {
+				if (ks && (strcmp(ks->name, nonjit_func) == 0)) {
 					good_kern_stack = true;
 					break;
 				}