Subject: Re: inbound connection problems when "netlink: test for all flags of the NLM_F_DUMP composite" commit applied

From: Jarek Poplawski <[email-masked]>
Date: Tue, 18 Jan 2011 21:07:16 +0100

On Tue, Jan 18, 2011 at 08:26:42PM +0100, Alessandro Suardi wrote:
> On Tue, Jan 18, 2011 at 7:47 PM, Jarek Poplawski <[email-masked]> wrote:
> > On Tue, Jan 18, 2011 at 07:28:52PM +0100, Jarek Poplawski wrote:
> >> On Tue, Jan 18, 2011 at 07:24:40PM +0100, Jan Engelhardt wrote:
> >> >
> >> > On Tuesday 2011-01-18 19:10, Alessandro Suardi wrote:
> >> > >On Tue, Jan 18, 2011 at 6:23 PM, Jarek Poplawski <[email-masked]> wrote:
> >> > >>
> >> > >> NLM_F_DUMP flags should be applied to GET requests only, eg. rtnetlink
> >> > >> tests message type to verify this. Since genetlink can't do the same
> >> > >> use "practical" test for ops->dumpit (assuming NEW request won't be
> >> > >> mixed with GET).
> >> ...
> >> > >2.6.37-git18 + netlink revert + this patch
> >> > > - fixes Avahi
> >> > > - breaks acpid
> >> > >Starting acpi daemon: RTNETLINK1 answers: Operation not supported
> >> > >acpid: error talking to the kernel via netlink
> >> >
> >> > Deducing from that, it is a GET-like request that was sent by acpid,
> >> > and the message type is one that has both a dumpit and a doit function.
> >> > So if EOPNOTSUPP now occurs on all message types that have both dumpit
> >> > and doit, you should have broken a lot more than just acpid.
> >>
> >> Right, we need something better here.
> >
> > On the other hand, until there is something better, we might try to
> > fix it at least for "normal" dumpit cases?
> >
> > Alessandro, could you try (with the netlink revert)?
...
> 2.6.37-git18 + netlink revert + this 2nd attempt
> 
>  appears to be good for me - both Avahi and acpid start up fine and I
>  can't see any other program misbehaving.
> 
> 
Alessandro, thanks for testing!

Jan, feel free to NAK if it can't help for your problem.

Jarek P.
---------------->
[PATCH v2] netlink: Fix possible NLM_F_DUMP misuse in genetlink

NLM_F_DUMP flags should be applied to GET requests only, eg. rtnetlink
tests message type to verify this. Since genetlink can't do the same
use "practical" test for ops->dumpit, assuming NEW request won't be
mixed with GET. Otherwise, it should work old way. Since, as reported
by Alessandro, apps like acpid use messages with ops->dumpit without
NLM_F_DUMP flags, there is no error reporting for this case.

Original patch by: Jan Engelhardt <[email-masked]>

Tested-by: Alessandro Suardi <[email-masked]>
Signed-off-by: Jarek Poplawski <[email-masked]>
Cc: Jan Engelhardt <[email-masked]>
Cc: Pablo Neira Ayuso <[email-masked]>
Cc: Jamal Hadi Salim <[email-masked]>
---

diff -Nurp a/net/netlink/genetlink.c b/net/netlink/genetlink.c
--- a/net/netlink/genetlink.c	2011-01-18 16:58:16.000000000 +0100
+++ b/net/netlink/genetlink.c	2011-01-18 19:36:25.000000000 +0100
@@ -519,15 +519,14 @@ static int genl_rcv_msg(struct sk_buff *
 	    security_netlink_recv(skb, CAP_NET_ADMIN))
 		return -EPERM;
 
-	if (nlh->nlmsg_flags & NLM_F_DUMP) {
-		if (ops->dumpit == NULL)
-			return -EOPNOTSUPP;
-
-		genl_unlock();
-		err = netlink_dump_start(net->genl_sock, skb, nlh,
-					 ops->dumpit, ops->done);
-		genl_lock();
-		return err;
+	if (ops->dumpit) {
+		if (nlh->nlmsg_flags & NLM_F_DUMP) {
+			genl_unlock();
+			err = netlink_dump_start(net->genl_sock, skb, nlh,
+						 ops->dumpit, ops->done);
+			genl_lock();
+			return err;
+		}
 	}
 
 	if (ops->doit == NULL)