[LSM-IPsec]: SELinux Authorize

This patch contains a fix for the previous patch that adds security
contexts to IPsec policies and security associations.  In the previous
patch, no authorization (besides the check for write permissions to
SAD and SPD) is required to delete IPsec policies and security
assocations with security contexts.  Thus a user authorized to change
SAD and SPD can bypass the IPsec policy authorization by simply
deleteing policies with security contexts.  To fix this security hole,
an additional authorization check is added for removing security
policies and security associations with security contexts.

Note that if no security context is supplied on add or present on
policy to be deleted, the SELinux module allows the change
unconditionally.  The hook is called on deletion when no context is
present, which we may want to change.  At present, I left it up to the
module.

LSM changes:

The patch adds two new LSM hooks: xfrm_policy_delete and
xfrm_state_delete.  The new hooks are necessary to authorize deletion
of IPsec policies that have security contexts.  The existing hooks
xfrm_policy_free and xfrm_state_free lack the context to do the
authorization, so I decided to split authorization of deletion and
memory management of security data, as is typical in the LSM
interface.

Use:

The new delete hooks are checked when xfrm_policy or xfrm_state are
deleted by either the xfrm_user interface (xfrm_get_policy,
xfrm_del_sa) or the pfkey interface (pfkey_spddelete, pfkey_delete).

SELinux changes:

The new policy_delete and state_delete functions are added.

Signed-off-by: Catherine Zhang <cxzhang@watson.ibm.com>
Signed-off-by: Trent Jaeger <tjaeger@cse.psu.edu>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 35 insertions, 4 deletions

diff --git a/security/selinux/xfrm.c b/security/selinux/xfrm.c
index abe99d8..0e24df4 100644
--- a/security/selinux/xfrm.c
+++ b/security/selinux/xfrm.c
@@ -132,10 +132,7 @@ static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_us
 		goto out;
 
 	/*
-	 * Does the subject have permission to set security or permission to
-	 * do the relabel?
-	 * Must be permitted to relabel from default socket type (process type)
-	 * to specified context
+	 * Does the subject have permission to set security context?
 	 */
 	rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 			  SECCLASS_ASSOCIATION,
@@ -201,6 +198,23 @@ void selinux_xfrm_policy_free(struct xfrm_policy *xp)
 }
 
 /*
+ * LSM hook implementation that authorizes deletion of labeled policies.
+ */
+int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
+{
+	struct task_security_struct *tsec = current->security;
+	struct xfrm_sec_ctx *ctx = xp->security;
+	int rc = 0;
+
+	if (ctx)
+		rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
+				  SECCLASS_ASSOCIATION,
+				  ASSOCIATION__SETCONTEXT, NULL);
+
+	return rc;
+}
+
+/*
  * LSM hook implementation that allocs and transfers sec_ctx spec to
  * xfrm_state.
  */
@@ -292,6 +306,23 @@ u32 selinux_socket_getpeer_dgram(struct sk_buff *skb)
 	return SECSID_NULL;
 }
 
+ /*
+  * LSM hook implementation that authorizes deletion of labeled SAs.
+  */
+int selinux_xfrm_state_delete(struct xfrm_state *x)
+{
+	struct task_security_struct *tsec = current->security;
+	struct xfrm_sec_ctx *ctx = x->security;
+	int rc = 0;
+
+	if (ctx)
+		rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
+				  SECCLASS_ASSOCIATION,
+				  ASSOCIATION__SETCONTEXT, NULL);
+
+	return rc;
+}
+
 /*
  * LSM hook that controls access to unlabelled packets.  If
  * a xfrm_state is authorizable (defined by macro) then it was