[NETLINK]: Do precise netlink message allocations where possible

Account for the netlink message header size directly in nlmsg_new()
instead of relying on the caller calculate it correctly.

Replaces error handling of message construction functions when
constructing notifications with bug traps since a failure implies
a bug in calculating the size of the skb.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 57 insertions, 23 deletions

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 4148e27..1df6cd45 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -306,6 +306,22 @@ errout:
 	return err;
 }
 
+static inline size_t fib_rule_nlmsg_size(struct fib_rules_ops *ops,
+					 struct fib_rule *rule)
+{
+	size_t payload = NLMSG_ALIGN(sizeof(struct fib_rule_hdr))
+			 + nla_total_size(IFNAMSIZ) /* FRA_IFNAME */
+			 + nla_total_size(4) /* FRA_PRIORITY */
+			 + nla_total_size(4) /* FRA_TABLE */
+			 + nla_total_size(4) /* FRA_FWMARK */
+			 + nla_total_size(4); /* FRA_FWMASK */
+
+	if (ops->nlmsg_payload)
+		payload += ops->nlmsg_payload(rule);
+
+	return payload;
+}
+
 static int fib_nl_fill_rule(struct sk_buff *skb, struct fib_rule *rule,
 			    u32 pid, u32 seq, int type, int flags,
 			    struct fib_rules_ops *ops)
@@ -384,15 +400,13 @@ static void notify_rule_change(int event, struct fib_rule *rule,
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+	skb = nlmsg_new(fib_rule_nlmsg_size(ops, rule), GFP_KERNEL);
 	if (skb == NULL)
 		goto errout;
 
 	err = fib_nl_fill_rule(skb, rule, pid, nlh->nlmsg_seq, event, 0, ops);
-	if (err < 0) {
-		kfree_skb(skb);
-		goto errout;
-	}
+	/* failure implies BUG in fib_rule_nlmsg_size() */
+	BUG_ON(err < 0);
 
 	err = rtnl_notify(skb, pid, ops->nlgroup, nlh, GFP_KERNEL);
 errout:
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index b4b4783..0e097ba 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2410,20 +2410,27 @@ static struct file_operations neigh_stat_seq_fops = {
 #endif /* CONFIG_PROC_FS */
 
 #ifdef CONFIG_ARPD
+static inline size_t neigh_nlmsg_size(void)
+{
+	return NLMSG_ALIGN(sizeof(struct ndmsg))
+	       + nla_total_size(MAX_ADDR_LEN) /* NDA_DST */
+	       + nla_total_size(MAX_ADDR_LEN) /* NDA_LLADDR */
+	       + nla_total_size(sizeof(struct nda_cacheinfo))
+	       + nla_total_size(4); /* NDA_PROBES */
+}
+
 static void __neigh_notify(struct neighbour *n, int type, int flags)
 {
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(NLMSG_GOODSIZE, GFP_ATOMIC);
+	skb = nlmsg_new(neigh_nlmsg_size(), GFP_ATOMIC);
 	if (skb == NULL)
 		goto errout;
 
 	err = neigh_fill_info(skb, n, 0, 0, type, flags);
-	if (err < 0) {
-		kfree_skb(skb);
-		goto errout;
-	}
+	/* failure implies BUG in neigh_nlmsg_size() */
+	BUG_ON(err < 0);
 
 	err = rtnl_notify(skb, 0, RTNLGRP_NEIGH, NULL, GFP_ATOMIC);
 errout:
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 02f3c79..50d6cb4 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -273,6 +273,25 @@ static void copy_rtnl_link_stats(struct rtnl_link_stats *a,
 	a->tx_compressed = b->tx_compressed;
 };
 
+static inline size_t if_nlmsg_size(int iwbuflen)
+{
+	return NLMSG_ALIGN(sizeof(struct ifinfomsg))
+	       + nla_total_size(IFNAMSIZ) /* IFLA_IFNAME */
+	       + nla_total_size(IFNAMSIZ) /* IFLA_QDISC */
+	       + nla_total_size(sizeof(struct rtnl_link_ifmap))
+	       + nla_total_size(sizeof(struct rtnl_link_stats))
+	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_ADDRESS */
+	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_BROADCAST */
+	       + nla_total_size(4) /* IFLA_TXQLEN */
+	       + nla_total_size(4) /* IFLA_WEIGHT */
+	       + nla_total_size(4) /* IFLA_MTU */
+	       + nla_total_size(4) /* IFLA_LINK */
+	       + nla_total_size(4) /* IFLA_MASTER */
+	       + nla_total_size(1) /* IFLA_OPERSTATE */
+	       + nla_total_size(1) /* IFLA_LINKMODE */
+	       + nla_total_size(iwbuflen);
+}
+
 static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 			    void *iwbuf, int iwbuflen, int type, u32 pid,
 			    u32 seq, u32 change, unsigned int flags)
@@ -558,7 +577,7 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 	struct sk_buff *nskb;
 	char *iw_buf = NULL, *iw = NULL;
 	int iw_buf_len = 0;
-	int err, payload;
+	int err;
 
 	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFLA_MAX, ifla_policy);
 	if (err < 0)
@@ -587,9 +606,7 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 	}
 #endif	/* CONFIG_NET_WIRELESS_RTNETLINK */
 
-	payload = NLMSG_ALIGN(sizeof(struct ifinfomsg) +
-			      nla_total_size(iw_buf_len));
-	nskb = nlmsg_new(nlmsg_total_size(payload), GFP_KERNEL);
+	nskb = nlmsg_new(if_nlmsg_size(iw_buf_len), GFP_KERNEL);
 	if (nskb == NULL) {
 		err = -ENOBUFS;
 		goto errout;
@@ -597,10 +614,8 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 
 	err = rtnl_fill_ifinfo(nskb, dev, iw, iw_buf_len, RTM_NEWLINK,
 			       NETLINK_CB(skb).pid, nlh->nlmsg_seq, 0, 0);
-	if (err <= 0) {
-		kfree_skb(nskb);
-		goto errout;
-	}
+	/* failure impilies BUG in if_nlmsg_size or wireless_rtnetlink_get */
+	BUG_ON(err < 0);
 
 	err = rtnl_unicast(nskb, NETLINK_CB(skb).pid);
 errout:
@@ -639,15 +654,13 @@ void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change)
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+	skb = nlmsg_new(if_nlmsg_size(0), GFP_KERNEL);
 	if (skb == NULL)
 		goto errout;
 
 	err = rtnl_fill_ifinfo(skb, dev, NULL, 0, type, 0, 0, change, 0);
-	if (err < 0) {
-		kfree_skb(skb);
-		goto errout;
-	}
+	/* failure implies BUG in if_nlmsg_size() */
+	BUG_ON(err < 0);
 
 	err = rtnl_notify(skb, 0, RTNLGRP_LINK, NULL, GFP_KERNEL);
 errout: