net: Switch to skb_dstref_steal/skb_dstref_restore for ip_route_input callers

Going forward skb_dst_set will assert that skb dst_entry
is empty during skb_dst_set. skb_dstref_steal is added to reset
existing entry without doing refcnt. skb_dstref_restore should
be used to restore the previous entry. Convert icmp_route_lookup
and ip_options_rcv_srr to these helpers. Add extra call to
skb_dstref_reset to icmp_route_lookup to clear the ip_route_input
entry.

Signed-off-by: Stanislav Fomichev <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/icmp.c

···
 			goto relookup_failed;
 		}
 		/* Ugh! */
-		orefdst = skb_in->_skb_refdst; /* save old refdst */
-		skb_dst_set(skb_in, NULL);
+		orefdst = skb_dstref_steal(skb_in);
 		err = ip_route_input(skb_in, fl4_dec.daddr, fl4_dec.saddr,
 				     dscp, rt2->dst.dev) ? -EINVAL : 0;
 
 		dst_release(&rt2->dst);
 		rt2 = skb_rtable(skb_in);
-		skb_in->_skb_refdst = orefdst; /* restore old refdst */
+		/* steal dst entry from skb_in, don't drop refcnt */
+		skb_dstref_steal(skb_in);
+		skb_dstref_restore(skb_in, orefdst);
 	}
 
 	if (err)

net/ipv4/ip_options.c

···
 		}
 		memcpy(&nexthop, &optptr[srrptr-1], 4);
 
-		orefdst = skb->_skb_refdst;
-		skb_dst_set(skb, NULL);
+		orefdst = skb_dstref_steal(skb);
 		err = ip_route_input(skb, nexthop, iph->saddr, ip4h_dscp(iph),
 				     dev) ? -EINVAL : 0;
 		rt2 = skb_rtable(skb);
 		if (err || (rt2->rt_type != RTN_UNICAST && rt2->rt_type != RTN_LOCAL)) {
 			skb_dst_drop(skb);
-			skb->_skb_refdst = orefdst;
+			skb_dstref_restore(skb, orefdst);
 			return -EINVAL;
 		}
 		refdst_drop(orefdst);