net: netlink -- Allow netlink_dump to return error code if protocol handler is missed

We've observed that in case if UDP diag module is not supported in kernel the netlink returns NLMSG_DONE without notifying a caller that handler is missed.

This patch makes netlink_dump to return error code instead.

So as example it become possible to detect such situation and handle it gracefully on userspace level.

Signed-off-by Cyrill Gorcunov <[email protected]>

CC David Miller <[email protected]>

CC Eric Dumazet <[email protected]>

CC Pavel Emelyanov <[email protected]>

---
 net/ipv4/inet_diag.c     |    5 ++++-
 net/netlink/af_netlink.c |    4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

Index: linux-2.6.git/net/ipv4/inet_diag.c
===================================================================

net/ipv4/inet_diag.c +4 -1

@@ -895,13 +895,16 @@ static int __inet_diag_dump(struct sk_bu
 		struct inet_diag_req_v2 *r, struct nlattr *bc)
 {
 	const struct inet_diag_handler *handler;
+	int err = 0;
 
 	handler = inet_diag_lock_handler(r->sdiag_protocol);
 	if (!IS_ERR(handler))
 		handler->dump(skb, cb, r, bc);
+	else
+		err = PTR_ERR(handler);
 	inet_diag_unlock_handler(handler);
 
-	return skb->len;
+	return err ? : skb->len;
 }
 
 static int inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)

Index: linux-2.6.git/net/netlink/af_netlink.c
===================================================================

net/netlink/af_netlink.c +0 -0

 	}
 
 	nlh = nlmsg_put_answer(skb, cb, NLMSG_DONE, sizeof(len), NLM_F_MULTI);

.

Quoted 9 lines

static int inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
Index: linux-2.6.git/net/netlink/af_netlink.c
===================================================================

net/netlink/af_netlink.c +0 -0

@@ -1740,6 +1740,10 @@ static int netlink_dump(struct sock *sk)
 		else
 			__netlink_sendskb(sk, skb);
 		return 0;

net/netlink/af_netlink.c static int netlink_dump(struct sock *sk) · line 1746

Quoted 4 lines

net/netlink/af_netlink.c +4 -0

+	} else if (len < 0) {
+		err = len;
+		nlk->cb = NULL;
+		goto errout_skb;

When family-level handler is absent and sock_diag returns error this error gets propagated back to user without this fix. Why do we need it in case we return error from protocol-level handler?

Quoted 9 lines · Pavel Emelyanov

Quoted 9 lines

static int inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
Index: linux-2.6.git/net/netlink/af_netlink.c
===================================================================

net/netlink/af_netlink.c +0 -0

@@ -1740,6 +1740,10 @@ static int netlink_dump(struct sock *sk)
 		else
 			__netlink_sendskb(sk, skb);
 		return 0;

Quoted 8 lines

net/netlink/af_netlink.c static int netlink_dump(struct sock *sk) · line 1746

Quoted 4 lines

net/netlink/af_netlink.c +4 -0

+	} else if (len < 0) {
+		err = len;
+		nlk->cb = NULL;
+		goto errout_skb;

When family-level handler is absent and sock_diag returns error this error gets propagated back to user without this fix. Why do we need it in case we return error from protocol-level handler?

Because as far as I can say the family-level handler already has such error returning code in __sock_diag_rcv_msg. Or you mean something else?