tcp: md5: rcu conversion

In order to be able to support proper RST messages for TCP MD5 flows, we
need to allow access to MD5 keys without locking listener socket.

This conversion is a nice cleanup, and shrinks size of timewait sockets
by 80 bytes.

IPv6 code reuses generic code found in IPv4 instead of duplicating it.

Control path uses GFP_KERNEL allocations instead of GFP_ATOMIC.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Shawn Lu <shawn.lu@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/tcp.h

@@ -486,8 +486,7 @@ struct tcp_timewait_sock {
 	u32			  tw_ts_recent;
 	long			  tw_ts_recent_stamp;
 #ifdef CONFIG_TCP_MD5SIG
-	u16			  tw_md5_keylen;
-	u8			  tw_md5_key[TCP_MD5SIG_MAXKEYLEN];
+	struct tcp_md5sig_key	*tw_md5_key;
 #endif
 	/* Few sockets in timewait have cookies; in that case, then this
 	 * object holds a reference to them (tw_cookie_values->kref).

include/net/tcp.h

@@ -1130,35 +1130,26 @@ static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
 /* MD5 Signature */
 struct crypto_hash;
 
+union tcp_md5_addr {
+	struct in_addr  a4;
+#if IS_ENABLED(CONFIG_IPV6)
+	struct in6_addr	a6;
+#endif
+};
+
 /* - key database */
 struct tcp_md5sig_key {
-	u8			*key;
+	struct hlist_node	node;
 	u8			keylen;
-};
-
-struct tcp4_md5sig_key {
-	struct tcp_md5sig_key	base;
-	__be32			addr;
-};
-
-struct tcp6_md5sig_key {
-	struct tcp_md5sig_key	base;
-#if 0
-	u32			scope_id;	/* XXX */
-#endif
-	struct in6_addr		addr;
+	u8			family; /* AF_INET or AF_INET6 */
+	union tcp_md5_addr	addr;
+	u8			key[TCP_MD5SIG_MAXKEYLEN];
+	struct rcu_head		rcu;
 };
 
 /* - sock block */
 struct tcp_md5sig_info {
-	struct tcp4_md5sig_key	*keys4;
-#if IS_ENABLED(CONFIG_IPV6)
-	struct tcp6_md5sig_key	*keys6;
-	u32			entries6;
-	u32			alloced6;
-#endif
-	u32			entries4;
-	u32			alloced4;
+	struct hlist_head	head;
 };
 
 /* - pseudo header */
@@ -1195,19 +1186,25 @@ extern int tcp_v4_md5_hash_skb(char *md5_hash, struct tcp_md5sig_key *key,
 			       const struct sock *sk,
 			       const struct request_sock *req,
 			       const struct sk_buff *skb);
-extern struct tcp_md5sig_key * tcp_v4_md5_lookup(struct sock *sk,
-						 struct sock *addr_sk);
-extern int tcp_v4_md5_do_add(struct sock *sk, __be32 addr, u8 *newkey,
-			     u8 newkeylen);
-extern int tcp_v4_md5_do_del(struct sock *sk, __be32 addr);
+extern int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
+			  int family, const u8 *newkey,
+			  u8 newkeylen, gfp_t gfp);
+extern int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
+			  int family);
+extern struct tcp_md5sig_key *tcp_v4_md5_lookup(struct sock *sk,
+					 struct sock *addr_sk);
 
 #ifdef CONFIG_TCP_MD5SIG
-#define tcp_twsk_md5_key(twsk)	((twsk)->tw_md5_keylen ? 		 \
-				 &(struct tcp_md5sig_key) {		 \
-					.key = (twsk)->tw_md5_key,	 \
-					.keylen = (twsk)->tw_md5_keylen, \
-				} : NULL)
+extern struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
+			const union tcp_md5_addr *addr, int family);
+#define tcp_twsk_md5_key(twsk)	((twsk)->tw_md5_key)
 #else
+static inline struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
+					 const union tcp_md5_addr *addr,
+					 int family)
+{
+	return NULL;
+}
 #define tcp_twsk_md5_key(twsk)	NULL
 #endif