bpf: harden sockmap program attach to ensure correct map type

When attaching a program to sockmap we need to check map type
is correct.

Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
Signed-off-by: John Fastabend <[e-mail]>
Acked-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

kernel/bpf/sockmap.c

···
 	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
 	struct bpf_prog *orig;
 
+	if (unlikely(map->map_type != BPF_MAP_TYPE_SOCKMAP))
+		return -EINVAL;
+
 	switch (type) {
 	case BPF_SK_SKB_STREAM_PARSER:
 		orig = xchg(&stab->bpf_parse, prog);

tools/testing/selftests/bpf/sockmap_verdict_prog.c

···
 	.max_entries = 20,
 };
 
+struct bpf_map_def SEC("maps") sock_map_break = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(int),
+	.max_entries = 20,
+};
+
 SEC("sk_skb2")
 int bpf_prog2(struct __sk_buff *skb)
 {

tools/testing/selftests/bpf/test_maps.c

···
 #define SOCKMAP_VERDICT_PROG "./sockmap_verdict_prog.o"
 static void test_sockmap(int task, void *data)
 {
+	int one = 1, map_fd_rx, map_fd_tx, map_fd_break, s, sc, rc;
+	struct bpf_map *bpf_map_rx, *bpf_map_tx, *bpf_map_break;
 	int ports[] = {50200, 50201, 50202, 50204};
 	int err, i, fd, sfd[6] = {0xdeadbeef};
 	u8 buf[20] = {0x0, 0x5, 0x3, 0x2, 0x1, 0x0};
-	int one = 1, map_fd_rx, map_fd_tx, s, sc, rc;
 	int parse_prog, verdict_prog;
-	struct bpf_map *bpf_map_rx, *bpf_map_tx;
 	struct sockaddr_in addr;
 	struct bpf_object *obj;
 	struct timeval to;
···
 		goto out_sockmap;
 	}
 
+	bpf_map_break = bpf_object__find_map_by_name(obj, "sock_map_break");
+	if (IS_ERR(bpf_map_break)) {
+		printf("Failed to load map tx from verdict prog\n");
+		goto out_sockmap;
+	}
+
+	map_fd_break = bpf_map__fd(bpf_map_break);
+	if (map_fd_break < 0) {
+		printf("Failed to get map tx fd\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_attach(parse_prog, map_fd_break,
+			      BPF_SK_SKB_STREAM_PARSER, 0);
+	if (!err) {
+		printf("Allowed attaching SK_SKB program to invalid map\n");
+		goto out_sockmap;
+	}
+
 	err = bpf_prog_attach(parse_prog, map_fd_rx,
 		      BPF_SK_SKB_STREAM_PARSER, 0);
 	if (err) {
-		printf("Failed bpf prog attach\n");
+		printf("Failed stream parser bpf prog attach\n");
 		goto out_sockmap;
 	}
 
 	err = bpf_prog_attach(verdict_prog, map_fd_rx,
 			      BPF_SK_SKB_STREAM_VERDICT, 0);
 	if (err) {
-		printf("Failed bpf prog attach\n");
+		printf("Failed stream verdict bpf prog attach\n");
 		goto out_sockmap;
 	}