neighbour: Allocate skb in neigh_get().

We will remove RTNL for neigh_get() and run it under RCU instead.

neigh_get_reply() and pneigh_get_reply() allocate skb with GFP_KERNEL.

Let's move the allocation before __dev_get_by_index() in neigh_get().

Now, neigh_get_reply() and pneigh_get_reply() are inlined and
rtnl_unicast() is factorised.

We will convert pneigh_lookup() to __pneigh_lookup() later.

Signed-off-by: Kuniyuki Iwashima <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: q2ven

net/core/neighbour.c

@@ -2988,27 +2988,6 @@ static inline size_t neigh_nlmsg_size(void)
 	       + nla_total_size(1); /* NDA_PROTOCOL */
 }
 
-static int neigh_get_reply(struct net *net, struct neighbour *neigh,
-			   u32 pid, u32 seq)
-{
-	struct sk_buff *skb;
-	int err = 0;
-
-	skb = nlmsg_new(neigh_nlmsg_size(), GFP_KERNEL);
-	if (!skb)
-		return -ENOBUFS;
-
-	err = neigh_fill_info(skb, neigh, pid, seq, RTM_NEWNEIGH, 0);
-	if (err) {
-		kfree_skb(skb);
-		goto errout;
-	}
-
-	err = rtnl_unicast(skb, net, pid);
-errout:
-	return err;
-}
-
 static inline size_t pneigh_nlmsg_size(void)
 {
 	return NLMSG_ALIGN(sizeof(struct ndmsg))
@@ -3017,34 +2996,16 @@ static inline size_t pneigh_nlmsg_size(void)
 	       + nla_total_size(1); /* NDA_PROTOCOL */
 }
 
-static int pneigh_get_reply(struct net *net, struct pneigh_entry *neigh,
-			    u32 pid, u32 seq, struct neigh_table *tbl)
-{
-	struct sk_buff *skb;
-	int err = 0;
-
-	skb = nlmsg_new(pneigh_nlmsg_size(), GFP_KERNEL);
-	if (!skb)
-		return -ENOBUFS;
-
-	err = pneigh_fill_info(skb, neigh, pid, seq, RTM_NEWNEIGH, 0, tbl);
-	if (err) {
-		kfree_skb(skb);
-		goto errout;
-	}
-
-	err = rtnl_unicast(skb, net, pid);
-errout:
-	return err;
-}
-
 static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		     struct netlink_ext_ack *extack)
 {
 	struct net *net = sock_net(in_skb->sk);
+	u32 pid = NETLINK_CB(in_skb).portid;
 	struct net_device *dev = NULL;
 	struct neigh_table *tbl = NULL;
+	u32 seq = nlh->nlmsg_seq;
 	struct neighbour *neigh;
+	struct sk_buff *skb;
 	struct ndmsg *ndm;
 	void *dst = NULL;
 	int err;
@@ -3053,11 +3014,19 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	if (IS_ERR(ndm))
 		return PTR_ERR(ndm);
 
+	if (ndm->ndm_flags & NTF_PROXY)
+		skb = nlmsg_new(neigh_nlmsg_size(), GFP_KERNEL);
+	else
+		skb = nlmsg_new(pneigh_nlmsg_size(), GFP_KERNEL);
+	if (!skb)
+		return -ENOBUFS;
+
 	if (ndm->ndm_ifindex) {
 		dev = __dev_get_by_index(net, ndm->ndm_ifindex);
 		if (!dev) {
 			NL_SET_ERR_MSG(extack, "Unknown device ifindex");
-			return -ENODEV;
+			err = -ENODEV;
+			goto err_free_skb;
 		}
 	}
 
@@ -3067,23 +3036,30 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		pn = pneigh_lookup(tbl, net, dst, dev, 0);
 		if (!pn) {
 			NL_SET_ERR_MSG(extack, "Proxy neighbour entry not found");
-			return -ENOENT;
+			err = -ENOENT;
+			goto err_free_skb;
 		}
-		return pneigh_get_reply(net, pn, NETLINK_CB(in_skb).portid,
-					nlh->nlmsg_seq, tbl);
-	}
-
-	neigh = neigh_lookup(tbl, dst, dev);
-	if (!neigh) {
-		NL_SET_ERR_MSG(extack, "Neighbour entry not found");
-		return -ENOENT;
-	}
 
-	err = neigh_get_reply(net, neigh, NETLINK_CB(in_skb).portid,
-			      nlh->nlmsg_seq);
+		err = pneigh_fill_info(skb, pn, pid, seq, RTM_NEWNEIGH, 0, tbl);
+		if (err)
+			goto err_free_skb;
+	} else {
+		neigh = neigh_lookup(tbl, dst, dev);
+		if (!neigh) {
+			NL_SET_ERR_MSG(extack, "Neighbour entry not found");
+			err = -ENOENT;
+			goto err_free_skb;
+		}
 
-	neigh_release(neigh);
+		err = neigh_fill_info(skb, neigh, pid, seq, RTM_NEWNEIGH, 0);
+		neigh_release(neigh);
+		if (err)
+			goto err_free_skb;
+	}
 
+	return rtnl_unicast(skb, net, pid);
+err_free_skb:
+	kfree_skb(skb);
 	return err;
 }