[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>

1 files changed, 30 insertions, 6 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 884d176e0082..e63b8a98fb4d 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -273,25 +273,49 @@ int ip_fib_check_default(__be32 gw, struct net_device *dev)
         return -1;
 }
 
+static inline size_t fib_nlmsg_size(struct fib_info *fi)
+{
+        size_t payload = NLMSG_ALIGN(sizeof(struct rtmsg))
+                         + nla_total_size(4) /* RTA_TABLE */
+                         + nla_total_size(4) /* RTA_DST */
+                         + nla_total_size(4) /* RTA_PRIORITY */
+                         + nla_total_size(4); /* RTA_PREFSRC */
+
+        /* 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 flow and gateway attribute */
+                nhsize += 2 * nla_total_size(4);
+
+                /* all nexthops are packed in a nested attribute */
+                payload += nla_total_size(fi->fib_nhs * nhsize);
+        }
+
+        return payload;
+}
+
 void rtmsg_fib(int event, __be32 key, struct fib_alias *fa,
                int dst_len, u32 tb_id, struct nl_info *info)
 {
         struct sk_buff *skb;
-        int payload = sizeof(struct rtmsg) + 256;
         u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
         int err = -ENOBUFS;
 
-        skb = nlmsg_new(nlmsg_total_size(payload), GFP_KERNEL);
+        skb = nlmsg_new(fib_nlmsg_size(fa->fa_info), GFP_KERNEL);
         if (skb == NULL)
                 goto errout;
 
         err = fib_dump_info(skb, info->pid, seq, event, tb_id,
                             fa->fa_type, fa->fa_scope, key, dst_len,
                             fa->fa_tos, fa->fa_info, 0);
-        if (err < 0) {
-                kfree_skb(skb);
-                goto errout;
-        }
+        /* failure implies BUG in fib_nlmsg_size() */
+        BUG_ON(err < 0);
 
         err = rtnl_notify(skb, info->pid, RTNLGRP_IPV4_ROUTE,
                           info->nlh, GFP_KERNEL);