[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>

2 files changed, 35 insertions, 5 deletions

diff --git a/net/decnet/dn_rules.c b/net/decnet/dn_rules.c
index e32d0c3d5a96..b7dfd04a9638 100644
--- a/net/decnet/dn_rules.c
+++ b/net/decnet/dn_rules.c
@@ -241,6 +241,12 @@ static u32 dn_fib_rule_default_pref(void)
         return 0;
 }
 
+static size_t dn_fib_rule_nlmsg_payload(struct fib_rule *rule)
+{
+        return nla_total_size(2) /* dst */
+               + nla_total_size(2); /* src */
+}
+
 int dn_fib_dump_rules(struct sk_buff *skb, struct netlink_callback *cb)
 {
         return fib_rules_dump(skb, cb, AF_DECnet);
diff --git a/net/decnet/dn_table.c b/net/decnet/dn_table.c
index 317904bb5896..e74b744254ab 100644
--- a/net/decnet/dn_table.c
+++ b/net/decnet/dn_table.c
@@ -263,6 +263,32 @@ static int dn_fib_nh_match(struct rtmsg *r, struct nlmsghdr *nlh, struct dn_kern
         return 0;
 }
 
+static inline size_t dn_fib_nlmsg_size(struct dn_fib_info *fi)
+{
+        size_t payload = NLMSG_ALIGN(struct rtmsg)
+                         + nla_total_size(4) /* RTA_TABLE */
+                         + nla_total_size(2) /* RTA_DST */
+                         + nla_total_size(4); /* RTA_PRIORITY */
+
+        /* space for nested metrics */
+        payload += nla_total_size((RTAX_MAX * nla_total_size(4)));
+
+        if (fi->fib_nhs) {
+                /* Also handles the special case fib_nhs == 1 */
+
+                /* each nexthop is packed in an attribute */
+                size_t nhsize = nla_total_size(sizeof(struct rtnexthop));
+
+                /* may contain a gateway attribute */
+                nhsize += nla_total_size(4);
+
+                /* all nexthops are packed in a nested attribute */
+                payload += nla_total_size(fi->fib_nhs * nhsize);
+        }
+
+        return payload;
+}
+
 static int dn_fib_dump_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
                         u32 tb_id, u8 type, u8 scope, void *dst, int dst_len,
                         struct dn_fib_info *fi, unsigned int flags)
@@ -335,17 +361,15 @@ static void dn_rtmsg_fib(int event, struct dn_fib_node *f, int z, u32 tb_id,
         u32 pid = req ? req->pid : 0;
         int err = -ENOBUFS;
 
-        skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+        skb = nlmsg_new(dn_fib_nlmsg_size(DN_FIB_INFO(f), GFP_KERNEL));
         if (skb == NULL)
                 goto errout;
 
         err = dn_fib_dump_info(skb, pid, nlh->nlmsg_seq, event, tb_id,
                                f->fn_type, f->fn_scope, &f->fn_key, z,
                                DN_FIB_INFO(f), 0);
-        if (err < 0) {
-                kfree_skb(skb);
-                goto errout;
-        }
+        /* failure implies BUG in dn_fib_nlmsg_size() */
+        BUG_ON(err < 0);
 
         err = rtnl_notify(skb, pid, RTNLGRP_DECnet_ROUTE, nlh, GFP_KERNEL);
 errout: