Patch "lwtunnel: fix autoload of lwt modules" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

lwtunnel: fix autoload of lwt modules

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
lwtunnel-fix-autoload-of-lwt-modules.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Ahern <[email protected]>
Date: Tue, 17 Jan 2017 14:57:36 -0800
Subject: lwtunnel: fix autoload of lwt modules

From: David Ahern <[email protected]>

[ Upstream commit 9ed59592e3e379b2e9557dc1d9e9ec8fcbb33f16]

Trying to add an mpls encap route when the MPLS modules are not loaded hangs. For example:

    CONFIG_MPLS=y
    CONFIG_NET_MPLS_GSO=m
    CONFIG_MPLS_ROUTING=m
    CONFIG_MPLS_IPTUNNEL=m

    $ ip route add 10.10.10.10/32 encap mpls 100 via inet 10.100.1.2

The ip command hangs:
root 880 826 0 21:25 pts/0 00:00:00 ip route add 10.10.10.10/32 encap mpls 100 via inet 10.100.1.2

    $ cat /proc/880/stack
    [<ffffffff81065a9b>] call_usermodehelper_exec+0xd6/0x134
    [<ffffffff81065efc>] __request_module+0x27b/0x30a
    [<ffffffff814542f6>] lwtunnel_build_state+0xe4/0x178
    [<ffffffff814aa1e4>] fib_create_info+0x47f/0xdd4
    [<ffffffff814ae451>] fib_table_insert+0x90/0x41f
    [<ffffffff814a8010>] inet_rtm_newroute+0x4b/0x52
    ...

modprobe is trying to load rtnl-lwt-MPLS:

root 881 5 0 21:25 ? 00:00:00 /sbin/modprobe -q -- rtnl-lwt-MPLS

and it hangs after loading mpls_router:

    $ cat /proc/881/stack
    [<ffffffff81441537>] rtnl_lock+0x12/0x14
    [<ffffffff8142ca2a>] register_netdevice_notifier+0x16/0x179
    [<ffffffffa0033025>] mpls_init+0x25/0x1000 [mpls_router]
    [<ffffffff81000471>] do_one_initcall+0x8e/0x13f
    [<ffffffff81119961>] do_init_module+0x5a/0x1e5
    [<ffffffff810bd070>] load_module+0x13bd/0x17d6
    ...

The problem is that lwtunnel_build_state is called with rtnl lock held preventing mpls_init from registering.

Given the potential references held by the time lwtunnel_build_state it can not drop the rtnl lock to the load module. So, extract the module loading code from lwtunnel_build_state into a new function to validate the encap type. The new function is called while converting the user request into a fib_config which is well before any table, device or fib entries are examined.

---
 include/net/lwtunnel.h  |   11 ++++++++
 net/core/lwtunnel.c     |   62 +++++++++++++++++++++++++++++++++++++++++++-----
 net/ipv4/fib_frontend.c |    8 ++++++
 net/ipv6/route.c        |   12 ++++++++-
 4 files changed, 86 insertions(+), 7 deletions(-)

@@ -106,6 +106,8 @@ int lwtunnel_encap_add_ops(const struct
 			   unsigned int num);
 int lwtunnel_encap_del_ops(const struct lwtunnel_encap_ops *op,
 			   unsigned int num);
+int lwtunnel_valid_encap_type(u16 encap_type);
+int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len);
 int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 			 struct nlattr *encap,
 			 unsigned int family, const void *cfg,

@@ -168,6 +170,15 @@ static inline int lwtunnel_encap_del_ops
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int lwtunnel_valid_encap_type(u16 encap_type)
+{
+	return -EOPNOTSUPP;
+}
+static inline int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len)
+{
+	return -EOPNOTSUPP;
+}
 
 static inline int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 				       struct nlattr *encap,

@@ -46,6 +46,7 @@
 #include <net/rtnetlink.h>
 #include <net/xfrm.h>
 #include <net/l3mdev.h>
+#include <net/lwtunnel.h>
 #include <trace/events/fib.h>
 
 #ifndef CONFIG_IP_MULTIPLE_TABLES

@@ -676,6 +677,10 @@ static int rtm_to_fib_config(struct net
 			cfg->fc_mx_len = nla_len(attr);
 			break;
 		case RTA_MULTIPATH:
+			err = lwtunnel_valid_encap_type_attr(nla_data(attr),
+							     nla_len(attr));
+			if (err < 0)
+				goto errout;
 			cfg->fc_mp = nla_data(attr);
 			cfg->fc_mp_len = nla_len(attr);
 			break;

@@ -690,6 +695,9 @@ static int rtm_to_fib_config(struct net
 			break;
 		case RTA_ENCAP_TYPE:
 			cfg->fc_encap_type = nla_get_u16(attr);
+			err = lwtunnel_valid_encap_type(cfg->fc_encap_type);
+			if (err < 0)
+				goto errout;
 			break;
 		}
 	}

@@ -2885,6 +2885,11 @@ static int rtm_to_fib6_config(struct sk_
 	if (tb[RTA_MULTIPATH]) {
 		cfg->fc_mp = nla_data(tb[RTA_MULTIPATH]);
 		cfg->fc_mp_len = nla_len(tb[RTA_MULTIPATH]);
+
+		err = lwtunnel_valid_encap_type_attr(cfg->fc_mp,
+						     cfg->fc_mp_len);
+		if (err < 0)
+			goto errout;
 	}
 
 	if (tb[RTA_PREF]) {

@@ -2898,9 +2903,14 @@ static int rtm_to_fib6_config(struct sk_
 	if (tb[RTA_ENCAP])
 		cfg->fc_encap = tb[RTA_ENCAP];
 
-	if (tb[RTA_ENCAP_TYPE])
+	if (tb[RTA_ENCAP_TYPE]) {
 		cfg->fc_encap_type = nla_get_u16(tb[RTA_ENCAP_TYPE]);
 
+		err = lwtunnel_valid_encap_type(cfg->fc_encap_type);
+		if (err < 0)
+			goto errout;
+	}
+
 	if (tb[RTA_EXPIRES]) {
 		unsigned long timeout = addrconf_timeout_fixup(nla_get_u32(tb[RTA_EXPIRES]), HZ);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net-lwtunnel-handle-lwtunnel_fill_encap-failure.patch queue-4.9/lwtunnel-fix-autoload-of-lwt-modules.patch queue-4.9/net-ipv4-fix-table-id-in-getroute-response.patch queue-4.9/net-mpls-fix-multipath-selection-for-lsr-use-case.patch