apparmor: add ns being viewed as a param to policy_view_capable()

Prepare for a tighter pairing of user namespaces and apparmor policy
namespaces, by making the ns to be viewed available and checking
that the user namespace level is the same as the policy ns level.

This strict pairing will be relaxed once true support of user namespaces
lands.

Signed-off-by: John Johansen <john.johansen@canonical.com>

1 files changed, 22 insertions, 3 deletions

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 0125de6..f092c04 100644
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -76,6 +76,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
+#include <linux/user_namespace.h>
 
 #include "include/apparmor.h"
 #include "include/capability.h"
@@ -89,6 +90,7 @@
 #include "include/policy_unpack.h"
 #include "include/resource.h"
 
+int unprivileged_userns_apparmor_policy = 1;
 
 const char *const aa_profile_mode_names[] = {
 	"enforce",
@@ -607,20 +609,37 @@ static int audit_policy(struct aa_profile *profile, int op, gfp_t gfp,
 			&sa, NULL);
 }
 
-bool policy_view_capable(void)
+/**
+ * policy_view_capable - check if viewing policy in at @ns is allowed
+ * ns: namespace being viewed by current task (may be NULL)
+ * Returns: true if viewing policy is allowed
+ *
+ * If @ns is NULL then the namespace being viewed is assumed to be the
+ * tasks current namespace.
+ */
+bool policy_view_capable(struct aa_ns *ns)
 {
 	struct user_namespace *user_ns = current_user_ns();
+	struct aa_ns *view_ns = aa_get_current_ns();
+	bool root_in_user_ns = uid_eq(current_euid(), make_kuid(user_ns, 0)) ||
+			       in_egroup_p(make_kgid(user_ns, 0));
 	bool response = false;
+	if (!ns)
+		ns = view_ns;
 
-	if (ns_capable(user_ns, CAP_MAC_ADMIN))
+	if (root_in_user_ns && aa_ns_visible(view_ns, ns, true) &&
+	    (user_ns == &init_user_ns ||
+	     (unprivileged_userns_apparmor_policy != 0 &&
+	      user_ns->level == view_ns->level)))
 		response = true;
+	aa_put_ns(view_ns);
 
 	return response;
 }
 
 bool policy_admin_capable(void)
 {
-	return policy_view_capable() && !aa_g_lock_policy;
+	return policy_view_capable(NULL) && !aa_g_lock_policy;
 }
 
 /**