bpf: Add BPF_PROG_TYPE_CGROUP_SKB attach type enforcement in BPF_LINK_CREATE

bpf_prog_attach uses attach_type_to_prog_type to enforce proper
attach type for BPF_PROG_TYPE_CGROUP_SKB. link_create uses
bpf_prog_get and relies on bpf_prog_attach_check_attach_type
to properly verify prog_type <> attach_type association.

Add missing attach_type enforcement for the link_create case.
Otherwise, it's currently possible to attach cgroup_skb prog
types to other cgroup hooks.

Fixes: af6eea5 ("bpf: Implement bpf_link-based cgroup BPF program attachment")
Link: https://lore.kernel.org/bpf/0000000000004792a90615a1dde0@google.com/
Reported-by: syzbot+838346b979830606c854@syzkaller.appspotmail.com
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240426231621.2716876-2-sdf@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: fomichev

kernel/bpf/syscall.c

@@ -3985,6 +3985,11 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
 			 * check permissions at attach time.
 			 */
 			return -EPERM;
+
+		ptype = attach_type_to_prog_type(attach_type);
+		if (prog->type != ptype)
+			return -EINVAL;
+
 		return prog->enforce_expected_attach_type &&
 			prog->expected_attach_type != attach_type ?
 			-EINVAL : 0;