net: Introduce sk_route_nocaps

TCP-MD5 sessions have intermittent failures, when route cache is
invalidated. ip_queue_xmit() has to find a new route, calls
sk_setup_caps(sk, &rt->u.dst), destroying the 

sk->sk_route_caps &= ~NETIF_F_GSO_MASK

that MD5 desperately try to make all over its way (from
tcp_transmit_skb() for example)

So we send few bad packets, and everything is fine when
tcp_transmit_skb() is called again for this socket.

Since ip_queue_xmit() is at a lower level than TCP-MD5, I chose to use a
socket field, sk_route_nocaps, containing bits to mask on sk_route_caps.

Reported-by: Bhaskar Dutta <bhaskie@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -177,6 +177,7 @@ struct sock_common {
   *		   %SO_OOBINLINE settings, %SO_TIMESTAMPING settings
   *	@sk_no_check: %SO_NO_CHECK setting, wether or not checkup packets
   *	@sk_route_caps: route capabilities (e.g. %NETIF_F_TSO)
+  *	@sk_route_nocaps: forbidden route capabilities (e.g NETIF_F_GSO_MASK)
   *	@sk_gso_type: GSO type (e.g. %SKB_GSO_TCPV4)
   *	@sk_gso_max_size: Maximum GSO segment size to build
   *	@sk_lingertime: %SO_LINGER l_linger setting
@@ -276,6 +277,7 @@ struct sock {
 	int			sk_forward_alloc;
 	gfp_t			sk_allocation;
 	int			sk_route_caps;
+	int			sk_route_nocaps;
 	int			sk_gso_type;
 	unsigned int		sk_gso_max_size;
 	int			sk_rcvlowat;
@@ -1335,6 +1337,12 @@ static inline int sk_can_gso(const struct sock *sk)
 
 extern void sk_setup_caps(struct sock *sk, struct dst_entry *dst);
 
+static inline void sk_nocaps_add(struct sock *sk, int flags)
+{
+	sk->sk_route_nocaps |= flags;
+	sk->sk_route_caps &= ~flags;
+}
+
 static inline int skb_copy_to_page(struct sock *sk, char __user *from,
 				   struct sk_buff *skb, struct page *page,
 				   int off, int copy)

net/core/sock.c

@@ -1231,6 +1231,7 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 	sk->sk_route_caps = dst->dev->features;
 	if (sk->sk_route_caps & NETIF_F_GSO)
 		sk->sk_route_caps |= NETIF_F_GSO_SOFTWARE;
+	sk->sk_route_caps &= ~sk->sk_route_nocaps;
 	if (sk_can_gso(sk)) {
 		if (dst->header_len) {
 			sk->sk_route_caps &= ~NETIF_F_GSO_MASK;

net/ipv4/tcp_ipv4.c

@@ -891,7 +891,7 @@ int tcp_v4_md5_do_add(struct sock *sk, __be32 addr,
 				kfree(newkey);
 				return -ENOMEM;
 			}
-			sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+			sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 		}
 		if (tcp_alloc_md5sig_pool(sk) == NULL) {
 			kfree(newkey);
@@ -1021,7 +1021,7 @@ static int tcp_v4_parse_md5_keys(struct sock *sk, char __user *optval,
 			return -EINVAL;
 
 		tp->md5sig_info = p;
-		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 	}
 
 	newkey = kmemdup(cmd.tcpm_key, cmd.tcpm_keylen, sk->sk_allocation);
@@ -1462,7 +1462,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 		if (newkey != NULL)
 			tcp_v4_md5_do_add(newsk, newinet->inet_daddr,
 					  newkey, key->keylen);
-		newsk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+		sk_nocaps_add(newsk, NETIF_F_GSO_MASK);
 	}
 #endif
 

net/ipv4/tcp_output.c

@@ -873,7 +873,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 #ifdef CONFIG_TCP_MD5SIG
 	/* Calculate the MD5 hash, as we have all we need now */
 	if (md5) {
-		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 		tp->af_specific->calc_md5_hash(opts.hash_location,
 					       md5, sk, NULL, skb);
 	}

net/ipv6/tcp_ipv6.c

@@ -604,7 +604,7 @@ static int tcp_v6_md5_do_add(struct sock *sk, struct in6_addr *peer,
 				kfree(newkey);
 				return -ENOMEM;
 			}
-			sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+			sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 		}
 		if (tcp_alloc_md5sig_pool(sk) == NULL) {
 			kfree(newkey);
@@ -741,7 +741,7 @@ static int tcp_v6_parse_md5_keys (struct sock *sk, char __user *optval,
 			return -ENOMEM;
 
 		tp->md5sig_info = p;
-		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
+		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 	}
 
 	newkey = kmemdup(cmd.tcpm_key, cmd.tcpm_keylen, GFP_KERNEL);