[PATCH AUTOSEL 4.14 110/123] netfilter: physdev: relax br_netfilter dependency

[Sasha Levin]

From: Florian Westphal <fw@xxxxxxxxx>

[ Upstream commit 8e2f311a68494a6677c1724bdcb10bada21af37c ]

Following command:
  iptables -D FORWARD -m physdev ...
causes connectivity loss in some setups.

Reason is that iptables userspace will probe kernel for the module revision
of the physdev patch, and physdev has an artificial dependency on
br_netfilter (xt_physdev use makes no sense unless a br_netfilter module
is loaded).

This causes the "phydev" module to be loaded, which in turn enables the
"call-iptables" infrastructure.

bridged packets might then get dropped by the iptables ruleset.

The better fix would be to change the "call-iptables" defaults to 0 and
enforce explicit setting to 1, but that breaks backwards compatibility.

This does the next best thing: add a request_module call to checkentry.
This was a stray '-D ... -m physdev' won't activate br_netfilter
anymore.

Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/net/netfilter/br_netfilter.h | 1 -
 net/bridge/br_netfilter_hooks.c      | 5 -----
 net/netfilter/xt_physdev.c           | 9 +++++++--
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/net/netfilter/br_netfilter.h b/include/net/netfilter/br_netfilter.h
index 74af19c3a8f7..a4ba601b5d04 100644
--- a/include/net/netfilter/br_netfilter.h
+++ b/include/net/netfilter/br_netfilter.h
@@ -49,7 +49,6 @@ static inline struct rtable *bridge_parent_rtable(const struct net_device *dev)
 }
 
 struct net_device *setup_pre_routing(struct sk_buff *skb);
-void br_netfilter_enable(void);
 
 #if IS_ENABLED(CONFIG_IPV6)
 int br_validate_ipv6(struct net *net, struct sk_buff *skb);
diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index 3f3859b8d49f..5fd283d9929e 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -881,11 +881,6 @@ static const struct nf_br_ops br_ops = {
 	.br_dev_xmit_hook =	br_nf_dev_xmit,
 };
 
-void br_netfilter_enable(void)
-{
-}
-EXPORT_SYMBOL_GPL(br_netfilter_enable);
-
 /* For br_nf_post_routing, we need (prio = NF_BR_PRI_LAST), because
  * br_dev_queue_push_xmit is called afterwards */
 static const struct nf_hook_ops br_nf_ops[] = {
diff --git a/net/netfilter/xt_physdev.c b/net/netfilter/xt_physdev.c
index bb33598e4530..ec247d8370e8 100644
--- a/net/netfilter/xt_physdev.c
+++ b/net/netfilter/xt_physdev.c
@@ -96,8 +96,7 @@ physdev_mt(const struct sk_buff *skb, struct xt_action_param *par)
 static int physdev_mt_check(const struct xt_mtchk_param *par)
 {
 	const struct xt_physdev_info *info = par->matchinfo;
-
-	br_netfilter_enable();
+	static bool brnf_probed __read_mostly;
 
 	if (!(info->bitmask & XT_PHYSDEV_OP_MASK) ||
 	    info->bitmask & ~XT_PHYSDEV_OP_MASK)
@@ -113,6 +112,12 @@ static int physdev_mt_check(const struct xt_mtchk_param *par)
 		if (par->hook_mask & (1 << NF_INET_LOCAL_OUT))
 			return -EINVAL;
 	}
+
+	if (!brnf_probed) {
+		brnf_probed = true;
+		request_module("br_netfilter");
+	}
+
 	return 0;
 }
 
-- 
2.19.1