IPsec: correct semantics for SELinux policy matching

Currently when an IPSec policy rule doesn't specify a security
context, it is assumed to be "unlabeled" by SELinux, and so
the IPSec policy rule fails to match to a flow that it would
otherwise match to, unless one has explicitly added an SELinux
policy rule allowing the flow to "polmatch" to the "unlabeled"
IPSec policy rules. In the absence of such an explicitly added
SELinux policy rule, the IPSec policy rule fails to match and
so the packet(s) flow in clear text without the otherwise applicable
xfrm(s) applied.

The above SELinux behavior violates the SELinux security notion of
"deny by default" which should actually translate to "encrypt by
default" in the above case.

This was first reported by Evgeniy Polyakov and the way James Morris
was seeing the problem was when connecting via IPsec to a
confined service on an SELinux box (vsftpd), which did not have the
appropriate SELinux policy permissions to send packets via IPsec.

With this patch applied, SELinux "polmatching" of flows Vs. IPSec
policy rules will only come into play when there's a explicit context
specified for the IPSec policy rule (which also means there's corresponding
SELinux policy allowing appropriate domains/flows to polmatch to this context).

Secondly, when a security module is loaded (in this case, SELinux), the
security_xfrm_policy_lookup() hook can return errors other than access denied,
such as -EINVAL.  We were not handling that correctly, and in fact
inverting the return logic and propagating a false "ok" back up to
xfrm_lookup(), which then allowed packets to pass as if they were not
associated with an xfrm policy.

The solution for this is to first ensure that errno values are
correctly propagated all the way back up through the various call chains
from security_xfrm_policy_lookup(), and handled correctly.

Then, flow_cache_lookup() is modified, so that if the policy resolver
fails (typically a permission denied via the security module), the flow
cache entry is killed rather than having a null policy assigned (which
indicates that the packet can pass freely).  This also forces any future
lookups for the same flow to consult the security module (e.g. SELinux)
for current security policy (rather than, say, caching the error on the
flow cache entry).

This patch: Fix the selinux side of things.

This makes sure SELinux polmatching of flow contexts to IPSec policy
rules comes into play only when an explicit context is associated
with the IPSec policy rule.

Also, this no longer defaults the context of a socket policy to
the context of the socket since the "no explicit context" case
is now handled properly.

Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 9 insertions, 15 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index 9b5fea81f55e..b200b9856f32 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -882,7 +882,8 @@ struct request_sock;
  *      Check permission when a flow selects a xfrm_policy for processing
  *      XFRMs on a packet.  The hook is called when selecting either a
  *      per-socket policy or a generic xfrm policy.
- *      Return 0 if permission is granted.
+ *      Return 0 if permission is granted, -ESRCH otherwise, or -errno
+ *      on other errors.
  * @xfrm_state_pol_flow_match:
  *      @x contains the state to match.
  *      @xp contains the policy to check for a match.
@@ -891,6 +892,7 @@ struct request_sock;
  * @xfrm_flow_state_match:
  *      @fl contains the flow key to match.
  *      @xfrm points to the xfrm_state to match.
+ *      @xp points to the xfrm_policy to match.
  *      Return 1 if there is a match.
  * @xfrm_decode_session:
  *      @skb points to skb to decode.
@@ -1388,7 +1390,8 @@ struct security_operations {
         int (*xfrm_policy_lookup)(struct xfrm_policy *xp, u32 fl_secid, u8 dir);
         int (*xfrm_state_pol_flow_match)(struct xfrm_state *x,
                         struct xfrm_policy *xp, struct flowi *fl);
-        int (*xfrm_flow_state_match)(struct flowi *fl, struct xfrm_state *xfrm);
+        int (*xfrm_flow_state_match)(struct flowi *fl, struct xfrm_state *xfrm,
+                        struct xfrm_policy *xp);
         int (*xfrm_decode_session)(struct sk_buff *skb, u32 *secid, int ckall);
 #endif  /* CONFIG_SECURITY_NETWORK_XFRM */
 
@@ -3120,11 +3123,6 @@ static inline int security_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm
         return security_ops->xfrm_policy_alloc_security(xp, sec_ctx, NULL);
 }
 
-static inline int security_xfrm_sock_policy_alloc(struct xfrm_policy *xp, struct sock *sk)
-{
-        return security_ops->xfrm_policy_alloc_security(xp, NULL, sk);
-}
-
 static inline int security_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 {
         return security_ops->xfrm_policy_clone_security(old, new);
@@ -3175,9 +3173,10 @@ static inline int security_xfrm_state_pol_flow_match(struct xfrm_state *x,
         return security_ops->xfrm_state_pol_flow_match(x, xp, fl);
 }
 
-static inline int security_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm)
+static inline int security_xfrm_flow_state_match(struct flowi *fl,
+                        struct xfrm_state *xfrm, struct xfrm_policy *xp)
 {
-        return security_ops->xfrm_flow_state_match(fl, xfrm);
+        return security_ops->xfrm_flow_state_match(fl, xfrm, xp);
 }
 
 static inline int security_xfrm_decode_session(struct sk_buff *skb, u32 *secid)
@@ -3197,11 +3196,6 @@ static inline int security_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm
         return 0;
 }
 
-static inline int security_xfrm_sock_policy_alloc(struct xfrm_policy *xp, struct sock *sk)
-{
-        return 0;
-}
-
 static inline int security_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 {
         return 0;
@@ -3249,7 +3243,7 @@ static inline int security_xfrm_state_pol_flow_match(struct xfrm_state *x,
 }
 
 static inline int security_xfrm_flow_state_match(struct flowi *fl,
-                                struct xfrm_state *xfrm)
+                        struct xfrm_state *xfrm, struct xfrm_policy *xp)
 {
         return 1;
 }