[NETLINK]: Don't BUG on undersized allocations

Currently netlink users BUG when the allocated skb for an event
notification is undersized. While this is certainly a kernel bug,
its not critical and crashing the kernel is too drastic, especially
when considering that these errors have appeared multiple times in
the past and it BUGs even if no listeners are present.

This patch replaces BUG by WARN_ON and changes the notification
functions to inform potential listeners of undersized allocations
using a unique error code (EMSGSIZE).

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 5 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index e63b8a98fb4d..be1028c9933e 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -314,9 +314,12 @@ void rtmsg_fib(int event, __be32 key, struct fib_alias *fa,
         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);
-        /* failure implies BUG in fib_nlmsg_size() */
-        BUG_ON(err < 0);
-
+        if (err < 0) {
+                /* -EMSGSIZE implies BUG in fib_nlmsg_size() */
+                WARN_ON(err == -EMSGSIZE);
+                kfree_skb(skb);
+                goto errout;
+        }
         err = rtnl_notify(skb, info->pid, RTNLGRP_IPV4_ROUTE,
                           info->nlh, GFP_KERNEL);
 errout:
@@ -960,7 +963,7 @@ int fib_dump_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
 
         nlh = nlmsg_put(skb, pid, seq, event, sizeof(*rtm), flags);
         if (nlh == NULL)
-                return -ENOBUFS;
+                return -EMSGSIZE;
 
         rtm = nlmsg_data(nlh);
         rtm->rtm_family = AF_INET;
@@ -1031,7 +1034,8 @@ int fib_dump_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
         return nlmsg_end(skb, nlh);
 
 nla_put_failure:
-        return nlmsg_cancel(skb, nlh);
+        nlmsg_cancel(skb, nlh);
+        return -EMSGSIZE;
 }
 
 /*