[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>

4 files changed, 31 insertions, 19 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 480ace9..c402036 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1140,7 +1140,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
 
 	nlh = nlmsg_put(skb, pid, seq, event, sizeof(*ifm), flags);
 	if (nlh == NULL)
-		return -ENOBUFS;
+		return -EMSGSIZE;
 
 	ifm = nlmsg_data(nlh);
 	ifm->ifa_family = AF_INET;
@@ -1167,7 +1167,8 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
 	return nlmsg_end(skb, nlh);
 
 nla_put_failure:
-	return nlmsg_cancel(skb, nlh);
+	nlmsg_cancel(skb, nlh);
+	return -EMSGSIZE;
 }
 
 static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
@@ -1225,9 +1226,12 @@ static void rtmsg_ifa(int event, struct in_ifaddr* ifa, struct nlmsghdr *nlh,
 		goto errout;
 
 	err = inet_fill_ifaddr(skb, ifa, pid, seq, event, 0);
-	/* failure implies BUG in inet_nlmsg_size() */
-	BUG_ON(err < 0);
-
+	if (err < 0) {
+		/* -EMSGSIZE implies BUG in inet_nlmsg_size() */
+		WARN_ON(err == -EMSGSIZE);
+		kfree_skb(skb);
+		goto errout;
+	}
 	err = rtnl_notify(skb, pid, RTNLGRP_IPV4_IFADDR, nlh, GFP_KERNEL);
 errout:
 	if (err < 0)
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index e63b8a9..be1028c 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;
 }
 
 /*
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 77761ac..9cd53ad 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -153,7 +153,7 @@ static int inet_csk_diag_fill(struct sock *sk,
 rtattr_failure:
 nlmsg_failure:
 	skb_trim(skb, b - skb->data);
-	return -1;
+	return -EMSGSIZE;
 }
 
 static int inet_twsk_diag_fill(struct inet_timewait_sock *tw,
@@ -209,7 +209,7 @@ static int inet_twsk_diag_fill(struct inet_timewait_sock *tw,
 	return skb->len;
 nlmsg_failure:
 	skb_trim(skb, previous_tail - skb->data);
-	return -1;
+	return -EMSGSIZE;
 }
 
 static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
@@ -274,11 +274,14 @@ static int inet_diag_get_exact(struct sk_buff *in_skb,
 	if (!rep)
 		goto out;
 
-	if (sk_diag_fill(sk, rep, req->idiag_ext,
-			 NETLINK_CB(in_skb).pid,
-			 nlh->nlmsg_seq, 0, nlh) <= 0)
-		BUG();
-
+	err = sk_diag_fill(sk, rep, req->idiag_ext,
+			   NETLINK_CB(in_skb).pid,
+			   nlh->nlmsg_seq, 0, nlh);
+	if (err < 0) {
+		WARN_ON(err == -EMSGSIZE);
+		kfree_skb(rep);
+		goto out;
+	}
 	err = netlink_unicast(idiagnl, rep, NETLINK_CB(in_skb).pid,
 			      MSG_DONTWAIT);
 	if (err > 0)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 2daa0dc..baee304 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2635,7 +2635,7 @@ static int rt_fill_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
 
 	nlh = nlmsg_put(skb, pid, seq, event, sizeof(*r), flags);
 	if (nlh == NULL)
-		return -ENOBUFS;
+		return -EMSGSIZE;
 
 	r = nlmsg_data(nlh);
 	r->rtm_family	 = AF_INET;
@@ -2718,7 +2718,8 @@ static int rt_fill_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;
 }
 
 int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr* nlh, void *arg)