Re: [patch net-next 03/12] ipmr: Add FIB notification access functions

On 09/21/2017 02:19 PM, Nikolay Aleksandrov wrote:

On 21/09/17 09:43, Jiri Pirko wrote:

quoted

From: Yotam Gigi <redacted>

Make the ipmr module register as a FIB notifier. To do that, implement both
the ipmr_seq_read and ipmr_dump ops.

The ipmr_seq_read op returns a sequence counter that is incremented on
every notification related operation done by the ipmr. To implement that,
add a sequence counter in the netns_ipv4 struct and increment it whenever a
new MFC route or VIF are added or deleted. The sequence operations are
protected by the RTNL lock.

The ipmr_dump iterates the list of MFC routes and the list of VIF entries
and sends notifications about them. The entries dump is done under RCU.

Signed-off-by: Yotam Gigi <redacted>
Reviewed-by: Ido Schimmel <redacted>
Signed-off-by: Jiri Pirko <redacted>
---
 include/linux/mroute.h   |  15 ++++++
 include/net/netns/ipv4.h |   3 ++
 net/ipv4/ipmr.c          | 135 ++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 151 insertions(+), 2 deletions(-)

[snip]

quoted

+
+static int ipmr_dump(struct net *net, struct notifier_block *nb)
+{
+	struct mr_table *mrt;
+	int err;
+
+	err = ipmr_rules_dump(net, nb);
+	if (err)
+		return err;
+
+	ipmr_for_each_table(mrt, net) {
+		struct vif_device *v = &mrt->vif_table[0];
+		struct mfc_cache *mfc;
+		int vifi;
+
+		/* Notifiy on table VIF entries */
+		for (vifi = 0; vifi < mrt->maxvif; vifi++, v++) {
+			if (!v->dev)
+				continue;
+
+			call_ipmr_vif_entry_notifier(nb, net, FIB_EVENT_VIF_ADD,
+						     v, vifi, mrt->id);
+		}

The VIF table is protected by mrt_lock (rwlock), here with RCU only
you're not guaranteed to keep v->dev. It can become NULL after the check above.
For details you can see vif_delete() in net/ipv4/ipmr.c. You need at least
mrt_lock for reading.

Hmm, that's interesting. That situation would lead the dump to be inconsistent,
thus eventually discarded, right? So I can also just make sure that the driver
ignores dev=NULL notifications and that would be enough to solve it.

I have to think about it a bit more, but anyway, maybe taking the mrt_lock for
the VIF dump is the right solution here.

Anyway, thanks for the review!

quoted

+
+		/* Notify on table MFC entries */
+		list_for_each_entry_rcu(mfc, &mrt->mfc_cache_list, list)
+			call_ipmr_mfc_entry_notifier(nb, net,
+						     FIB_EVENT_ENTRY_ADD, mfc,
+						     mrt->id);
+	}
+
+	return 0;
+}
+
+static const struct fib_notifier_ops ipmr_notifier_ops_template = {
+	.family		= RTNL_FAMILY_IPMR,
+	.fib_seq_read	= ipmr_seq_read,
+	.fib_dump	= ipmr_dump,
+	.owner		= THIS_MODULE,
+};
+
+int __net_init ipmr_notifier_init(struct net *net)
+{
+	struct fib_notifier_ops *ops;
+
+	net->ipv4.ipmr_seq = 0;
+
+	ops = fib_notifier_ops_register(&ipmr_notifier_ops_template, net);
+	if (IS_ERR(ops))
+		return PTR_ERR(ops);
+	net->ipv4.ipmr_notifier_ops = ops;
+
+	return 0;
+}
+
+static void __net_exit ipmr_notifier_exit(struct net *net)
+{
+	fib_notifier_ops_unregister(net->ipv4.ipmr_notifier_ops);
+	net->ipv4.ipmr_notifier_ops = NULL;
+}
+
 /* Setup for IP multicast routing */
 static int __net_init ipmr_net_init(struct net *net)
 {
 	int err;
 
+	err = ipmr_notifier_init(net);
+	if (err)
+		goto ipmr_notifier_fail;
+
 	err = ipmr_rules_init(net);
 	if (err < 0)
-		goto fail;
+		goto ipmr_rules_fail;
 
 #ifdef CONFIG_PROC_FS
 	err = -ENOMEM;

@@ -3074,7 +3202,9 @@ static int __net_init ipmr_net_init(struct net *net)
 proc_vif_fail:
 	ipmr_rules_exit(net);
 #endif
-fail:
+ipmr_rules_fail:
+	ipmr_notifier_exit(net);
+ipmr_notifier_fail:
 	return err;
 }
 

@@ -3084,6 +3214,7 @@ static void __net_exit ipmr_net_exit(struct net *net)
 	remove_proc_entry("ip_mr_cache", net->proc_net);
 	remove_proc_entry("ip_mr_vif", net->proc_net);
 #endif
+	ipmr_notifier_exit(net);
 	ipmr_rules_exit(net);
 }