bpf, xdp, samples: Fix null pointer dereference in *_user code

Memset on the pointer right after malloc can cause a NULL pointer
deference if it failed to allocate memory. A simple fix is to
replace malloc()/memset() pair with a simple call to calloc().

Fixes: 0fca931 ("samples/bpf: program demonstrating access to xdp_rxq_info")
Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>

samples/bpf/xdp_monitor_user.c

@@ -509,11 +509,8 @@ static void *alloc_rec_per_cpu(int record_size)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
 	void *array;
-	size_t size;
 
-	size = record_size * nr_cpus;
-	array = malloc(size);
-	memset(array, 0, size);
+	array = calloc(nr_cpus, record_size);
 	if (!array) {
 		fprintf(stderr, "Mem alloc error (nr_cpus:%u)\n", nr_cpus);
 		exit(EXIT_FAIL_MEM);
@@ -528,8 +525,7 @@ static struct stats_record *alloc_stats_record(void)
 	int i;
 
 	/* Alloc main stats_record structure */
-	rec = malloc(sizeof(*rec));
-	memset(rec, 0, sizeof(*rec));
+	rec = calloc(1, sizeof(*rec));
 	if (!rec) {
 		fprintf(stderr, "Mem alloc error\n");
 		exit(EXIT_FAIL_MEM);

samples/bpf/xdp_redirect_cpu_user.c

@@ -207,11 +207,8 @@ static struct datarec *alloc_record_per_cpu(void)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
 	struct datarec *array;
-	size_t size;
 
-	size = sizeof(struct datarec) * nr_cpus;
-	array = malloc(size);
-	memset(array, 0, size);
+	array = calloc(nr_cpus, sizeof(struct datarec));
 	if (!array) {
 		fprintf(stderr, "Mem alloc error (nr_cpus:%u)\n", nr_cpus);
 		exit(EXIT_FAIL_MEM);
@@ -226,11 +223,11 @@ static struct stats_record *alloc_stats_record(void)
 
 	size = sizeof(*rec) + n_cpus * sizeof(struct record);
 	rec = malloc(size);
-	memset(rec, 0, size);
 	if (!rec) {
 		fprintf(stderr, "Mem alloc error\n");
 		exit(EXIT_FAIL_MEM);
 	}
+	memset(rec, 0, size);
 	rec->rx_cnt.cpu    = alloc_record_per_cpu();
 	rec->redir_err.cpu = alloc_record_per_cpu();
 	rec->kthread.cpu   = alloc_record_per_cpu();

samples/bpf/xdp_rxq_info_user.c

@@ -198,11 +198,8 @@ static struct datarec *alloc_record_per_cpu(void)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
 	struct datarec *array;
-	size_t size;
 
-	size = sizeof(struct datarec) * nr_cpus;
-	array = malloc(size);
-	memset(array, 0, size);
+	array = calloc(nr_cpus, sizeof(struct datarec));
 	if (!array) {
 		fprintf(stderr, "Mem alloc error (nr_cpus:%u)\n", nr_cpus);
 		exit(EXIT_FAIL_MEM);
@@ -214,11 +211,8 @@ static struct record *alloc_record_per_rxq(void)
 {
 	unsigned int nr_rxqs = bpf_map__def(rx_queue_index_map)->max_entries;
 	struct record *array;
-	size_t size;
 
-	size = sizeof(struct record) * nr_rxqs;
-	array = malloc(size);
-	memset(array, 0, size);
+	array = calloc(nr_rxqs, sizeof(struct record));
 	if (!array) {
 		fprintf(stderr, "Mem alloc error (nr_rxqs:%u)\n", nr_rxqs);
 		exit(EXIT_FAIL_MEM);
@@ -232,8 +226,7 @@ static struct stats_record *alloc_stats_record(void)
 	struct stats_record *rec;
 	int i;
 
-	rec = malloc(sizeof(*rec));
-	memset(rec, 0, sizeof(*rec));
+	rec = calloc(1, sizeof(struct stats_record));
 	if (!rec) {
 		fprintf(stderr, "Mem alloc error\n");
 		exit(EXIT_FAIL_MEM);