inet: Avoid potential NULL peer dereference.

We handle NULL in rt{,6}_set_peer but then our caller will try to pass
that NULL pointer into inet_putpeer() which isn't ready for it.

Fix this by moving the NULL check one level up, and then remove the
now unnecessary NULL check from inetpeer_ptr_set_peer().
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/inetpeer.h

@@ -104,7 +104,7 @@ static inline bool inetpeer_ptr_set_peer(unsigned long *ptr, struct inet_peer *p
 	unsigned long val = (unsigned long) peer;
 	unsigned long orig = *ptr;
 
-	if (!(orig & INETPEER_BASE_BIT) || !val ||
+	if (!(orig & INETPEER_BASE_BIT) ||
 	    cmpxchg(ptr, orig, val) != orig)
 		return false;
 	return true;

net/ipv4/route.c

@@ -1333,11 +1333,12 @@ void rt_bind_peer(struct rtable *rt, __be32 daddr, int create)
 		return;
 
 	peer = inet_getpeer_v4(base, daddr, create);
-
-	if (!rt_set_peer(rt, peer))
-		inet_putpeer(peer);
-	else
-		rt->rt_peer_genid = rt_peer_genid();
+	if (peer) {
+		if (!rt_set_peer(rt, peer))
+			inet_putpeer(peer);
+		else
+			rt->rt_peer_genid = rt_peer_genid();
+	}
 }
 
 /*

net/ipv6/route.c

@@ -313,10 +313,12 @@ void rt6_bind_peer(struct rt6_info *rt, int create)
 		return;
 
 	peer = inet_getpeer_v6(base, &rt->rt6i_dst.addr, create);
-	if (!rt6_set_peer(rt, peer))
-		inet_putpeer(peer);
-	else
-		rt->rt6i_peer_genid = rt6_peer_genid();
+	if (peer) {
+		if (!rt6_set_peer(rt, peer))
+			inet_putpeer(peer);
+		else
+			rt->rt6i_peer_genid = rt6_peer_genid();
+	}
 }
 
 static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,