net: rtnetlink: rtnl_fill_statsinfo(): Permit non-EMSGSIZE error returns

Obtaining stats for the IFLA_STATS_LINK_OFFLOAD_XSTATS nest involves a HW
access, and can fail for more reasons than just netlink message size
exhaustion. Therefore do not always return -EMSGSIZE on the failure path,
but respect the error code provided by the callee. Set the error explicitly
where it is reasonable to assume -EMSGSIZE as the failure reason.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -5177,8 +5177,10 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 		attr = nla_reserve_64bit(skb, IFLA_STATS_LINK_64,
 					 sizeof(struct rtnl_link_stats64),
 					 IFLA_STATS_UNSPEC);
-		if (!attr)
+		if (!attr) {
+			err = -EMSGSIZE;
 			goto nla_put_failure;
+		}
 
 		sp = nla_data(attr);
 		dev_get_stats(dev, sp);
@@ -5191,8 +5193,10 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 			*idxattr = IFLA_STATS_LINK_XSTATS;
 			attr = nla_nest_start_noflag(skb,
 						     IFLA_STATS_LINK_XSTATS);
-			if (!attr)
+			if (!attr) {
+				err = -EMSGSIZE;
 				goto nla_put_failure;
+			}
 
 			err = ops->fill_linkxstats(skb, dev, prividx, *idxattr);
 			nla_nest_end(skb, attr);
@@ -5214,8 +5218,10 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 			*idxattr = IFLA_STATS_LINK_XSTATS_SLAVE;
 			attr = nla_nest_start_noflag(skb,
 						     IFLA_STATS_LINK_XSTATS_SLAVE);
-			if (!attr)
+			if (!attr) {
+				err = -EMSGSIZE;
 				goto nla_put_failure;
+			}
 
 			err = ops->fill_linkxstats(skb, dev, prividx, *idxattr);
 			nla_nest_end(skb, attr);
@@ -5233,8 +5239,10 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 		*idxattr = IFLA_STATS_LINK_OFFLOAD_XSTATS;
 		attr = nla_nest_start_noflag(skb,
 					     IFLA_STATS_LINK_OFFLOAD_XSTATS);
-		if (!attr)
+		if (!attr) {
+			err = -EMSGSIZE;
 			goto nla_put_failure;
+		}
 
 		err = rtnl_offload_xstats_fill(skb, dev, prividx,
 					       off_filter_mask, extack);
@@ -5253,8 +5261,10 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 
 		*idxattr = IFLA_STATS_AF_SPEC;
 		attr = nla_nest_start_noflag(skb, IFLA_STATS_AF_SPEC);
-		if (!attr)
+		if (!attr) {
+			err = -EMSGSIZE;
 			goto nla_put_failure;
+		}
 
 		rcu_read_lock();
 		list_for_each_entry_rcu(af_ops, &rtnl_af_ops, list) {
@@ -5298,7 +5308,7 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 	else
 		nlmsg_end(skb, nlh);
 
-	return -EMSGSIZE;
+	return err;
 }
 
 static size_t if_nlmsg_stats_size(const struct net_device *dev,