selinux: process labeled IPsec TCP SYN-ACK packets properly in selinux_ip_postroute()

Due to difficulty in arriving at the proper security label for
TCP SYN-ACK packets in selinux_ip_postroute(), we need to check packets
while/before they are undergoing XFRM transforms instead of waiting
until afterwards so that we can determine the correct security label.

Reported-by: Janak Desai <Janak.Desai@gtri.gatech.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Paul Moore <pmoore@redhat.com>

1 files changed, 35 insertions, 7 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 95cb1345257d..a98228e7b91d 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4846,22 +4846,31 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
          * as fast and as clean as possible. */
         if (!selinux_policycap_netpeer)
                 return selinux_ip_postroute_compat(skb, ifindex, family);
+
+        secmark_active = selinux_secmark_enabled();
+        peerlbl_active = selinux_peerlbl_enabled();
+        if (!secmark_active && !peerlbl_active)
+                return NF_ACCEPT;
+
+        sk = skb->sk;
+
 #ifdef CONFIG_XFRM
         /* If skb->dst->xfrm is non-NULL then the packet is undergoing an IPsec
          * packet transformation so allow the packet to pass without any checks
          * since we'll have another chance to perform access control checks
          * when the packet is on it's final way out.
          * NOTE: there appear to be some IPv6 multicast cases where skb->dst
-         *       is NULL, in this case go ahead and apply access control. */
-        if (skb_dst(skb) != NULL && skb_dst(skb)->xfrm != NULL)
+         *       is NULL, in this case go ahead and apply access control.
+         * NOTE: if this is a local socket (skb->sk != NULL) that is in the
+         *       TCP listening state we cannot wait until the XFRM processing
+         *       is done as we will miss out on the SA label if we do;
+         *       unfortunately, this means more work, but it is only once per
+         *       connection. */
+        if (skb_dst(skb) != NULL && skb_dst(skb)->xfrm != NULL &&
+            !(sk != NULL && sk->sk_state == TCP_LISTEN))
                 return NF_ACCEPT;
 #endif
-        secmark_active = selinux_secmark_enabled();
-        peerlbl_active = selinux_peerlbl_enabled();
-        if (!secmark_active && !peerlbl_active)
-                return NF_ACCEPT;
 
-        sk = skb->sk;
         if (sk == NULL) {
                 /* Without an associated socket the packet is either coming
                  * from the kernel or it is being forwarded; check the packet
@@ -4889,6 +4898,25 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
                 struct sk_security_struct *sksec = sk->sk_security;
                 if (selinux_skb_peerlbl_sid(skb, family, &skb_sid))
                         return NF_DROP;
+                /* At this point, if the returned skb peerlbl is SECSID_NULL
+                 * and the packet has been through at least one XFRM
+                 * transformation then we must be dealing with the "final"
+                 * form of labeled IPsec packet; since we've already applied
+                 * all of our access controls on this packet we can safely
+                 * pass the packet. */
+                if (skb_sid == SECSID_NULL) {
+                        switch (family) {
+                        case PF_INET:
+                                if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
+                                        return NF_ACCEPT;
+                                break;
+                        case PF_INET6:
+                                if (IP6CB(skb)->flags & IP6SKB_XFRM_TRANSFORMED)
+                                        return NF_ACCEPT;
+                        default:
+                                return NF_DROP_ERR(-ECONNREFUSED);
+                        }
+                }
                 if (selinux_conn_sid(sksec->sid, skb_sid, &peer_sid))
                         return NF_DROP;
                 secmark_perm = PACKET__SEND;