neighbour: Move two validations from neigh_get() to neigh_valid_get_req().

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

neigh_get() returns -EINVAL in the following cases:

  * NDA_DST is not specified
  * Both ndm->ndm_ifindex and NTF_PROXY are not specified

These validations do not require RCU.

Let's move them to neigh_valid_get_req().

While at it, the extack string for the first case is replaced with
NL_SET_ERR_ATTR_MISS().

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

@@ -2935,6 +2935,11 @@ static struct ndmsg *neigh_valid_get_req(const struct nlmsghdr *nlh,
 		return ERR_PTR(-EINVAL);
 	}
 
+	if (!(ndm->ndm_flags & NTF_PROXY) && !ndm->ndm_ifindex) {
+		NL_SET_ERR_MSG(extack, "No device specified");
+		return ERR_PTR(-EINVAL);
+	}
+
 	err = nlmsg_parse_deprecated_strict(nlh, sizeof(struct ndmsg), tb,
 					    NDA_MAX, nda_policy, extack);
 	if (err < 0)
@@ -2947,18 +2952,23 @@ static struct ndmsg *neigh_valid_get_req(const struct nlmsghdr *nlh,
 	}
 
 	for (i = 0; i <= NDA_MAX; ++i) {
-		if (!tb[i])
-			continue;
-
 		switch (i) {
 		case NDA_DST:
+			if (!tb[i]) {
+				NL_SET_ERR_ATTR_MISS(extack, NULL, NDA_DST);
+				return ERR_PTR(-EINVAL);
+			}
+
 			if (nla_len(tb[i]) != (int)(*tbl)->key_len) {
 				NL_SET_ERR_MSG(extack, "Invalid network address in neighbor get request");
 				return ERR_PTR(-EINVAL);
 			}
 			*dst = nla_data(tb[i]);
 			break;
 		default:
+			if (!tb[i])
+				continue;
+
 			NL_SET_ERR_MSG(extack, "Unsupported attribute in neighbor get request");
 			return ERR_PTR(-EINVAL);
 		}
@@ -3051,11 +3061,6 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		}
 	}
 
-	if (!dst) {
-		NL_SET_ERR_MSG(extack, "Network address not specified");
-		return -EINVAL;
-	}
-
 	if (ndm->ndm_flags & NTF_PROXY) {
 		struct pneigh_entry *pn;
 
@@ -3068,11 +3073,6 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 					nlh->nlmsg_seq, tbl);
 	}
 
-	if (!dev) {
-		NL_SET_ERR_MSG(extack, "No device specified");
-		return -EINVAL;
-	}
-
 	neigh = neigh_lookup(tbl, dst, dev);
 	if (!neigh) {
 		NL_SET_ERR_MSG(extack, "Neighbour entry not found");