af_unix: Remove UNIX_ABSTRACT() macro and test sun_path[0] instead.

In BSD and abstract address cases, we store sockets in the hash table with
keys between 0 and UNIX_HASH_SIZE - 1.  However, the hash saved in a socket
varies depending on its address type; sockets with BSD addresses always
have UNIX_HASH_SIZE in their unix_sk(sk)->addr->hash.

This is just for the UNIX_ABSTRACT() macro used to check the address type.
The difference of the saved hashes comes from the first byte of the address
in the first place.  So, we can test it directly.

Then we can keep a real hash in each socket and replace unix_table_lock
with per-hash locks in the later patch.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/unix/af_unix.c

@@ -134,8 +134,6 @@ static struct hlist_head *unix_sockets_unbound(void *addr)
 	return &unix_socket_table[UNIX_HASH_SIZE + hash];
 }
 
-#define UNIX_ABSTRACT(sk)	(unix_sk(sk)->addr->hash < UNIX_HASH_SIZE)
-
 #ifdef CONFIG_SECURITY_NETWORK
 static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
@@ -3292,9 +3290,9 @@ static int unix_seq_show(struct seq_file *seq, void *v)
 			i = 0;
 			len = u->addr->len -
 				offsetof(struct sockaddr_un, sun_path);
-			if (!UNIX_ABSTRACT(s))
+			if (u->addr->name->sun_path[0]) {
 				len--;
-			else {
+			} else {
 				seq_putc(seq, '@');
 				i++;
 			}

tools/testing/selftests/bpf/progs/bpf_iter_unix.c

@@ -49,7 +49,7 @@ int dump_unix(struct bpf_iter__unix *ctx)
 		       sock_i_ino(sk));
 
 	if (unix_sk->addr) {
-		if (!UNIX_ABSTRACT(unix_sk)) {
+		if (unix_sk->addr->name->sun_path[0]) {
 			BPF_SEQ_PRINTF(seq, " %s", unix_sk->addr->name->sun_path);
 		} else {
 			/* The name of the abstract UNIX domain socket starts

tools/testing/selftests/bpf/progs/bpf_tracing_net.h

@@ -6,8 +6,6 @@
 #define AF_INET6		10
 
 #define __SO_ACCEPTCON		(1 << 16)
-#define UNIX_HASH_SIZE		256
-#define UNIX_ABSTRACT(unix_sk)	(unix_sk->addr->hash < UNIX_HASH_SIZE)
 
 #define SOL_TCP			6
 #define TCP_CONGESTION		13

tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c

@@ -23,7 +23,7 @@ int BPF_PROG(unix_listen, struct socket *sock, int backlog)
 	if (!unix_sk)
 		return 0;
 
-	if (!UNIX_ABSTRACT(unix_sk))
+	if (unix_sk->addr->name->sun_path[0])
 		return 0;
 
 	len = unix_sk->addr->len - sizeof(short);