xfrm: Add possibility to set the default to block if we have no policy

[ Upstream commit 2d151d39073aff498358543801fca0f670fea981 ]

As the default we assume the traffic to pass, if we have no
matching IPsec policy. With this patch, we have a possibility to
change this default from allow to block. It can be configured
via netlink. Each direction (input/output/forward) can be
configured separately. With the default to block configuered,
we need allow policies for all packet flows we accept.
We do not use default policy lookup for the loopback device.

v1->v2
 - fix compiling when XFRM is disabled
 - Reported-by: kernel test robot <lkp@intel.com>

Co-developed-by: Christian Langrock <christian.langrock@secunet.com>
Signed-off-by: Christian Langrock <christian.langrock@secunet.com>
Co-developed-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

3 files changed, 47 insertions, 6 deletions

diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index 22e1bc72b979..b694ff0963cc 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -64,6 +64,13 @@ struct netns_xfrm {
 	u32			sysctl_aevent_rseqth;
 	int			sysctl_larval_drop;
 	u32			sysctl_acq_expires;
+
+	u8			policy_default;
+#define XFRM_POL_DEFAULT_IN	1
+#define XFRM_POL_DEFAULT_OUT	2
+#define XFRM_POL_DEFAULT_FWD	4
+#define XFRM_POL_DEFAULT_MASK	7
+
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header	*sysctl_hdr;
 #endif
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 0049a7459649..988886f95e5b 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1088,6 +1088,22 @@ xfrm_state_addr_cmp(const struct xfrm_tmpl *tmpl, const struct xfrm_state *x, un
 }
 
 #ifdef CONFIG_XFRM
+static inline bool
+xfrm_default_allow(struct net *net, int dir)
+{
+	u8 def = net->xfrm.policy_default;
+
+	switch (dir) {
+	case XFRM_POLICY_IN:
+		return def & XFRM_POL_DEFAULT_IN ? false : true;
+	case XFRM_POLICY_OUT:
+		return def & XFRM_POL_DEFAULT_OUT ? false : true;
+	case XFRM_POLICY_FWD:
+		return def & XFRM_POL_DEFAULT_FWD ? false : true;
+	}
+	return false;
+}
+
 int __xfrm_policy_check(struct sock *, int dir, struct sk_buff *skb,
 			unsigned short family);
 
@@ -1101,9 +1117,13 @@ static inline int __xfrm_policy_check2(struct sock *sk, int dir,
 	if (sk && sk->sk_policy[XFRM_POLICY_IN])
 		return __xfrm_policy_check(sk, ndir, skb, family);
 
-	return	(!net->xfrm.policy_count[dir] && !secpath_exists(skb)) ||
-		(skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY)) ||
-		__xfrm_policy_check(sk, ndir, skb, family);
+	if (xfrm_default_allow(net, dir))
+		return (!net->xfrm.policy_count[dir] && !secpath_exists(skb)) ||
+		       (skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY)) ||
+		       __xfrm_policy_check(sk, ndir, skb, family);
+	else
+		return (skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY)) ||
+		       __xfrm_policy_check(sk, ndir, skb, family);
 }
 
 static inline int xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb, unsigned short family)
@@ -1155,9 +1175,13 @@ static inline int xfrm_route_forward(struct sk_buff *skb, unsigned short family)
 {
 	struct net *net = dev_net(skb->dev);
 
-	return	!net->xfrm.policy_count[XFRM_POLICY_OUT] ||
-		(skb_dst(skb)->flags & DST_NOXFRM) ||
-		__xfrm_route_forward(skb, family);
+	if (xfrm_default_allow(net, XFRM_POLICY_FWD))
+		return !net->xfrm.policy_count[XFRM_POLICY_OUT] ||
+			(skb_dst(skb)->flags & DST_NOXFRM) ||
+			__xfrm_route_forward(skb, family);
+	else
+		return (skb_dst(skb)->flags & DST_NOXFRM) ||
+			__xfrm_route_forward(skb, family);
 }
 
 static inline int xfrm4_route_forward(struct sk_buff *skb)
diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 90ddb49fce84..b963e1acf65a 100644
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -213,6 +213,11 @@ enum {
 	XFRM_MSG_GETSPDINFO,
 #define XFRM_MSG_GETSPDINFO XFRM_MSG_GETSPDINFO
 
+	XFRM_MSG_SETDEFAULT,
+#define XFRM_MSG_SETDEFAULT XFRM_MSG_SETDEFAULT
+	XFRM_MSG_GETDEFAULT,
+#define XFRM_MSG_GETDEFAULT XFRM_MSG_GETDEFAULT
+
 	XFRM_MSG_MAPPING,
 #define XFRM_MSG_MAPPING XFRM_MSG_MAPPING
 	__XFRM_MSG_MAX
@@ -515,6 +520,11 @@ struct xfrm_user_offload {
 #define XFRM_OFFLOAD_IPV6	1
 #define XFRM_OFFLOAD_INBOUND	2
 
+struct xfrm_userpolicy_default {
+	__u8				dirmask;
+	__u8				action;
+};
+
 #ifndef __KERNEL__
 /* backwards compatibility for userspace */
 #define XFRMGRP_ACQUIRE		1