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, 41 insertions, 12 deletions

diff --git a/security/selinux/xfrm.c b/security/selinux/xfrm.c
index 3e742b8..675b995 100644
--- a/security/selinux/xfrm.c
+++ b/security/selinux/xfrm.c
@@ -77,8 +77,8 @@ static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  */
 int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 fl_secid, u8 dir)
 {
-	int rc = 0;
-	u32 sel_sid = SECINITSID_UNLABELED;
+	int rc;
+	u32 sel_sid;
 	struct xfrm_sec_ctx *ctx;
 
 	/* Context sid is either set to label or ANY_ASSOC */
@@ -88,11 +88,21 @@ int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 fl_secid, u8 dir)
 
 		sel_sid = ctx->ctx_sid;
 	}
+	else
+		/*
+		 * All flows should be treated as polmatch'ing an
+		 * otherwise applicable "non-labeled" policy. This
+		 * would prevent inadvertent "leaks".
+		 */
+		return 0;
 
 	rc = avc_has_perm(fl_secid, sel_sid, SECCLASS_ASSOCIATION,
 			  ASSOCIATION__POLMATCH,
 			  NULL);
 
+	if (rc == -EACCES)
+		rc = -ESRCH;
+
 	return rc;
 }
 
@@ -108,15 +118,20 @@ int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *
 	u32 pol_sid;
 	int err;
 
-	if (x->security)
-		state_sid = x->security->ctx_sid;
-	else
-		state_sid = SECINITSID_UNLABELED;
-
-	if (xp->security)
+	if (xp->security) {
+		if (!x->security)
+			/* unlabeled SA and labeled policy can't match */
+			return 0;
+		else
+			state_sid = x->security->ctx_sid;
 		pol_sid = xp->security->ctx_sid;
-	else
-		pol_sid = SECINITSID_UNLABELED;
+	} else
+		if (x->security)
+			/* unlabeled policy and labeled SA can't match */
+			return 0;
+		else
+			/* unlabeled policy and unlabeled SA match all flows */
+			return 1;
 
 	err = avc_has_perm(state_sid, pol_sid, SECCLASS_ASSOCIATION,
 			  ASSOCIATION__POLMATCH,
@@ -125,7 +140,11 @@ int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *
 	if (err)
 		return 0;
 
-	return selinux_xfrm_flow_state_match(fl, x);
+	err = avc_has_perm(fl->secid, state_sid, SECCLASS_ASSOCIATION,
+			  ASSOCIATION__SENDTO,
+			  NULL)? 0:1;
+
+	return err;
 }
 
 /*
@@ -133,12 +152,22 @@ int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *
  * can use a given security association.
  */
 
-int selinux_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm)
+int selinux_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm,
+				  struct xfrm_policy *xp)
 {
 	int rc = 0;
 	u32 sel_sid = SECINITSID_UNLABELED;
 	struct xfrm_sec_ctx *ctx;
 
+	if (!xp->security)
+		if (!xfrm->security)
+			return 1;
+		else
+			return 0;
+	else
+		if (!xfrm->security)
+			return 0;
+
 	/* Context sid is either set to label or ANY_ASSOC */
 	if ((ctx = xfrm->security)) {
 		if (!selinux_authorizable_ctx(ctx))