scsi: libcxgbi: fib6_ino reference in rt6_info is rcu protected

The fib6_info reference in rt6_info is rcu protected. Add a helper
to extract prefsrc from and update cxgbi_check_route6 to use it.

Fixes: 0153167a ("net/ipv6: Remove rt6i_prefsrc")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/scsi/cxgbi/libcxgbi.c

@@ -784,7 +784,8 @@ cxgbi_check_route6(struct sockaddr *dst_addr, int ifindex)
 	csk->mtu = mtu;
 	csk->dst = dst;
 
-	if (!rt->from || ipv6_addr_any(&rt->from->fib6_prefsrc.addr)) {
+	rt6_get_prefsrc(rt, &pref_saddr);
+	if (ipv6_addr_any(&pref_saddr)) {
 		struct inet6_dev *idev = ip6_dst_idev((struct dst_entry *)rt);
 
 		err = ipv6_dev_get_saddr(&init_net, idev ? idev->dev : NULL,
@@ -794,8 +795,6 @@ cxgbi_check_route6(struct sockaddr *dst_addr, int ifindex)
 				&daddr6->sin6_addr);
 			goto rel_rt;
 		}
-	} else {
-		pref_saddr = rt->from->fib6_prefsrc.addr;
 	}
 
 	csk->csk_family = AF_INET6;

include/net/ip6_fib.h

@@ -412,6 +412,25 @@ int fib6_add(struct fib6_node *root, struct fib6_info *rt,
 	     struct nl_info *info, struct netlink_ext_ack *extack);
 int fib6_del(struct fib6_info *rt, struct nl_info *info);
 
+static inline
+void rt6_get_prefsrc(const struct rt6_info *rt, struct in6_addr *addr)
+{
+	const struct fib6_info *from;
+
+	rcu_read_lock();
+
+	from = rcu_dereference(rt->from);
+	if (from) {
+		*addr = from->fib6_prefsrc.addr;
+	} else {
+		struct in6_addr in6_zero = {};
+
+		*addr = in6_zero;
+	}
+
+	rcu_read_unlock();
+}
+
 static inline struct net_device *fib6_info_nh_dev(const struct fib6_info *f6i)
 {
 	return f6i->fib6_nh.nh_dev;