ipv6: lockless IPV6_FLOWINFO_SEND implementation

np->sndflow reads are racy.

Use one bit ftom atomic inet->inet_flags instead,
IPV6_FLOWINFO_SEND setsockopt() can be lockless.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ipv6.h

@@ -243,8 +243,7 @@ struct ipv6_pinfo {
 	} rxopt;
 
 	/* sockopt flags */
-	__u8			sndflow:1,
-				srcprefs:3;	/* 001: prefer temporary address
+	__u8			srcprefs:3;	/* 001: prefer temporary address
 						 * 010: prefer public address
 						 * 100: prefer care-of address
 						 */

include/net/inet_sock.h

@@ -277,6 +277,7 @@ enum {
 	INET_FLAGS_RECVERR6	= 26,
 	INET_FLAGS_REPFLOW	= 27,
 	INET_FLAGS_RTALERT_ISOLATE = 28,
+	INET_FLAGS_SNDFLOW	= 29,
 };
 
 /* cmsg flags for inet */

net/dccp/ipv6.c

@@ -844,7 +844,7 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 
 	memset(&fl6, 0, sizeof(fl6));
 
-	if (np->sndflow) {
+	if (inet6_test_bit(SNDFLOW, sk)) {
 		fl6.flowlabel = usin->sin6_flowinfo & IPV6_FLOWINFO_MASK;
 		IP6_ECN_flow_init(fl6.flowlabel);
 		if (fl6.flowlabel & IPV6_FLOWLABEL_MASK) {

net/ipv4/ping.c

@@ -899,7 +899,6 @@ int ping_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int flags,
 
 #if IS_ENABLED(CONFIG_IPV6)
 	} else if (family == AF_INET6) {
-		struct ipv6_pinfo *np = inet6_sk(sk);
 		struct ipv6hdr *ip6 = ipv6_hdr(skb);
 		DECLARE_SOCKADDR(struct sockaddr_in6 *, sin6, msg->msg_name);
 
@@ -908,7 +907,7 @@ int ping_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int flags,
 			sin6->sin6_port = 0;
 			sin6->sin6_addr = ip6->saddr;
 			sin6->sin6_flowinfo = 0;
-			if (np->sndflow)
+			if (inet6_test_bit(SNDFLOW, sk))
 				sin6->sin6_flowinfo = ip6_flowinfo(ip6);
 			sin6->sin6_scope_id =
 				ipv6_iface_scope_id(&sin6->sin6_addr,

net/ipv6/af_inet6.c

@@ -537,7 +537,7 @@ int inet6_getname(struct socket *sock, struct sockaddr *uaddr,
 		}
 		sin->sin6_port = inet->inet_dport;
 		sin->sin6_addr = sk->sk_v6_daddr;
-		if (np->sndflow)
+		if (inet6_test_bit(SNDFLOW, sk))
 			sin->sin6_flowinfo = np->flow_label;
 		BPF_CGROUP_RUN_SA_PROG(sk, (struct sockaddr *)sin,
 				       CGROUP_INET6_GETPEERNAME);

net/ipv6/datagram.c

@@ -80,7 +80,8 @@ int ip6_datagram_dst_update(struct sock *sk, bool fix_sk_saddr)
 	struct flowi6 fl6;
 	int err = 0;
 
-	if (np->sndflow && (np->flow_label & IPV6_FLOWLABEL_MASK)) {
+	if (inet6_test_bit(SNDFLOW, sk) &&
+	    (np->flow_label & IPV6_FLOWLABEL_MASK)) {
 		flowlabel = fl6_sock_lookup(sk, np->flow_label);
 		if (IS_ERR(flowlabel))
 			return -EINVAL;
@@ -163,7 +164,7 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 	if (usin->sin6_family != AF_INET6)
 		return -EAFNOSUPPORT;
 
-	if (np->sndflow)
+	if (inet6_test_bit(SNDFLOW, sk))
 		fl6_flowlabel = usin->sin6_flowinfo & IPV6_FLOWINFO_MASK;
 
 	if (ipv6_addr_any(&usin->sin6_addr)) {
@@ -491,7 +492,7 @@ int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 			const struct ipv6hdr *ip6h = container_of((struct in6_addr *)(nh + serr->addr_offset),
 								  struct ipv6hdr, daddr);
 			sin->sin6_addr = ip6h->daddr;
-			if (np->sndflow)
+			if (inet6_test_bit(SNDFLOW, sk))
 				sin->sin6_flowinfo = ip6_flowinfo(ip6h);
 			sin->sin6_scope_id =
 				ipv6_iface_scope_id(&sin->sin6_addr,

net/ipv6/ipv6_sockglue.c

@@ -500,6 +500,11 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 			return -EINVAL;
 		WRITE_ONCE(np->pmtudisc, val);
 		return 0;
+	case IPV6_FLOWINFO_SEND:
+		if (optlen < sizeof(int))
+			return -EINVAL;
+		inet6_assign_bit(SNDFLOW, sk, valbool);
+		return 0;
 	}
 	if (needs_rtnl)
 		rtnl_lock();
@@ -948,12 +953,6 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 			goto e_inval;
 		retv = ip6_ra_control(sk, val);
 		break;
-	case IPV6_FLOWINFO_SEND:
-		if (optlen < sizeof(int))
-			goto e_inval;
-		np->sndflow = valbool;
-		retv = 0;
-		break;
 	case IPV6_FLOWLABEL_MGR:
 		retv = ipv6_flowlabel_opt(sk, optval, optlen);
 		break;
@@ -1381,7 +1380,7 @@ int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case IPV6_FLOWINFO_SEND:
-		val = np->sndflow;
+		val = inet6_test_bit(SNDFLOW, sk);
 		break;
 
 	case IPV6_FLOWLABEL_MGR:

net/ipv6/ping.c

@@ -89,7 +89,7 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			return -EAFNOSUPPORT;
 		}
 		daddr = &(u->sin6_addr);
-		if (np->sndflow)
+		if (inet6_test_bit(SNDFLOW, sk))
 			fl6.flowlabel = u->sin6_flowinfo & IPV6_FLOWINFO_MASK;
 		if (__ipv6_addr_needs_scope_id(ipv6_addr_type(daddr)))
 			oif = u->sin6_scope_id;

net/ipv6/raw.c

@@ -795,7 +795,7 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			return -EINVAL;
 
 		daddr = &sin6->sin6_addr;
-		if (np->sndflow) {
+		if (inet6_test_bit(SNDFLOW, sk)) {
 			fl6.flowlabel = sin6->sin6_flowinfo&IPV6_FLOWINFO_MASK;
 			if (fl6.flowlabel&IPV6_FLOWLABEL_MASK) {
 				flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);

net/ipv6/tcp_ipv6.c

@@ -163,7 +163,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 
 	memset(&fl6, 0, sizeof(fl6));
 
-	if (np->sndflow) {
+	if (inet6_test_bit(SNDFLOW, sk)) {
 		fl6.flowlabel = usin->sin6_flowinfo&IPV6_FLOWINFO_MASK;
 		IP6_ECN_flow_init(fl6.flowlabel);
 		if (fl6.flowlabel&IPV6_FLOWLABEL_MASK) {

net/ipv6/udp.c

@@ -1429,7 +1429,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		fl6->fl6_dport = sin6->sin6_port;
 		daddr = &sin6->sin6_addr;
 
-		if (np->sndflow) {
+		if (inet6_test_bit(SNDFLOW, sk)) {
 			fl6->flowlabel = sin6->sin6_flowinfo&IPV6_FLOWINFO_MASK;
 			if (fl6->flowlabel & IPV6_FLOWLABEL_MASK) {
 				flowlabel = fl6_sock_lookup(sk, fl6->flowlabel);

net/l2tp/l2tp_ip6.c

@@ -431,7 +431,7 @@ static int l2tp_ip6_getname(struct socket *sock, struct sockaddr *uaddr,
 			return -ENOTCONN;
 		lsa->l2tp_conn_id = lsk->peer_conn_id;
 		lsa->l2tp_addr = sk->sk_v6_daddr;
-		if (np->sndflow)
+		if (inet6_test_bit(SNDFLOW, sk))
 			lsa->l2tp_flowinfo = np->flow_label;
 	} else {
 		if (ipv6_addr_any(&sk->sk_v6_rcv_saddr))
@@ -529,7 +529,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			return -EAFNOSUPPORT;
 
 		daddr = &lsa->l2tp_addr;
-		if (np->sndflow) {
+		if (inet6_test_bit(SNDFLOW, sk)) {
 			fl6.flowlabel = lsa->l2tp_flowinfo & IPV6_FLOWINFO_MASK;
 			if (fl6.flowlabel & IPV6_FLOWLABEL_MASK) {
 				flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);

net/sctp/ipv6.c

@@ -296,7 +296,8 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr,
 	if (t->flowlabel & SCTP_FLOWLABEL_SET_MASK)
 		fl6->flowlabel = htonl(t->flowlabel & SCTP_FLOWLABEL_VAL_MASK);
 
-	if (np->sndflow && (fl6->flowlabel & IPV6_FLOWLABEL_MASK)) {
+	if (inet6_test_bit(SNDFLOW, sk) &&
+	    (fl6->flowlabel & IPV6_FLOWLABEL_MASK)) {
 		struct ip6_flowlabel *flowlabel;
 
 		flowlabel = fl6_sock_lookup(sk, fl6->flowlabel);