[PATCH AUTOSEL for 4.4 091/115] net: xfrm: allow clearing socket xfrm policies.

[Sasha Levin <Alexander.Levin@microsoft.com>]

From: Lorenzo Colitti <lorenzo@google.com>

[ Upstream commit be8f8284cd897af2482d4e54fbc2bdfc15557259 ]

Currently it is possible to add or update socket policies, but
not clear them. Therefore, once a socket policy has been applied,
the socket cannot be used for unencrypted traffic.

This patch allows (privileged) users to clear socket policies by
passing in a NULL pointer and zero length argument to the
{IP,IPV6}_{IPSEC,XFRM}_POLICY setsockopts. This results in both
the incoming and outgoing policies being cleared.

The simple approach taken in this patch cannot clear socket
policies in only one direction. If desired this could be added
in the future, for example by continuing to pass in a length of
zero (which currently is guaranteed to return EMSGSIZE) and
making the policy be a pointer to an integer that contains one
of the XFRM_POLICY_{IN,OUT} enum values.

An alternative would have been to interpret the length as a
signed integer and use XFRM_POLICY_IN (i.e., 0) to clear the
input policy and -XFRM_POLICY_OUT (i.e., -1) to clear the output
policy.

Tested: https://android-review.googlesource.com/539816
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 net/xfrm/xfrm_policy.c | 2 +-
 net/xfrm/xfrm_state.c  | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 4b09a9eaa35f..d95cb69460f0 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1313,7 +1313,7 @@ EXPORT_SYMBOL(xfrm_policy_delete);
 
 int xfrm_sk_policy_insert(struct sock *sk, int dir, struct xfrm_policy *pol)
 {
-	struct net *net = xp_net(pol);
+	struct net *net = sock_net(sk);
 	struct xfrm_policy *old_pol;
 
 #ifdef CONFIG_XFRM_SUB_POLICY
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 9895a8c56d8c..96d664e198bf 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1845,6 +1845,13 @@ int xfrm_user_policy(struct sock *sk, int optname, u8 __user *optval, int optlen
 	struct xfrm_mgr *km;
 	struct xfrm_policy *pol = NULL;
 
+	if (!optval && !optlen) {
+		xfrm_sk_policy_insert(sk, XFRM_POLICY_IN, NULL);
+		xfrm_sk_policy_insert(sk, XFRM_POLICY_OUT, NULL);
+		__sk_dst_reset(sk);
+		return 0;
+	}
+
 	if (optlen <= 0 || optlen > PAGE_SIZE)
 		return -EMSGSIZE;
 
-- 
2.14.1