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: 174a79ff95 ("bpf: sockmap with sk redirect support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/sockmap.c

@@ -794,6 +794,9 @@ int sock_map_attach_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)
 	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);