netlink: let core handle error cases in dump operations

After commit b5a89915 ("netlink: handle EMSGSIZE errors
in the core"), we can remove some code that was not 100 % correct
anyway.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240306102426.245689-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/rtnetlink.c

@@ -2267,11 +2267,8 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 				       nlh->nlmsg_seq, 0, flags,
 				       ext_filter_mask, 0, NULL, 0,
 				       netnsid, GFP_KERNEL);
-		if (err < 0) {
-			if (likely(skb->len))
-				err = skb->len;
+		if (err < 0)
 			break;
-		}
 	}
 	cb->seq = tgt_net->dev_base_seq;
 	nl_dump_check_consistent(cb, nlmsg_hdr(skb));

net/ipv4/devinet.c

@@ -1900,8 +1900,6 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 			goto done;
 	}
 done:
-	if (err < 0 && likely(skb->len))
-		err = skb->len;
 	if (fillargs.netnsid >= 0)
 		put_net(tgt_net);
 	rcu_read_unlock();
@@ -2312,8 +2310,6 @@ static int inet_netconf_dump_devconf(struct sk_buff *skb,
 		ctx->all_default++;
 	}
 done:
-	if (err < 0 && likely(skb->len))
-		err = skb->len;
 	rcu_read_unlock();
 	return err;
 }

net/ipv4/fib_frontend.c

@@ -1026,8 +1026,6 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 			goto unlock;
 		}
 		err = fib_table_dump(tb, skb, cb, &filter);
-		if (err < 0 && skb->len)
-			err = skb->len;
 		goto unlock;
 	}
 
@@ -1045,11 +1043,8 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 				memset(&cb->args[2], 0, sizeof(cb->args) -
 						 2 * sizeof(cb->args[0]));
 			err = fib_table_dump(tb, skb, cb, &filter);
-			if (err < 0) {
-				if (likely(skb->len))
-					err = skb->len;
+			if (err < 0)
 				goto out;
-			}
 			dumped = 1;
 next:
 			e++;

net/ipv6/addrconf.c

@@ -793,8 +793,6 @@ static int inet6_netconf_dump_devconf(struct sk_buff *skb,
 		ctx->all_default++;
 	}
 done:
-	if (err < 0 && likely(skb->len))
-		err = skb->len;
 	rcu_read_unlock();
 	return err;
 }
@@ -6158,11 +6156,8 @@ static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 					NETLINK_CB(cb->skb).portid,
 					cb->nlh->nlmsg_seq,
 					RTM_NEWLINK, NLM_F_MULTI);
-		if (err < 0) {
-			if (likely(skb->len))
-				err = skb->len;
+		if (err < 0)
 			break;
-		}
 	}
 	rcu_read_unlock();