capabilities: introduce security_capable_noaudit

Exactly like security_capable except don't audit any denials.  This is for
places where the kernel may make decisions about what to do if a task has a
given capability, but which failing that capability is not a sign of a
security policy violation.  An example is checking if a task has
CAP_SYS_ADMIN to lower it's likelyhood of being killed by the oom killer.
This check is not a security violation if it is denied.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>

include/linux/security.h

@@ -1668,6 +1668,8 @@ int security_capset(struct cred *new, const struct cred *old,
 		    const kernel_cap_t *permitted);
 int security_capable(const struct cred *cred, struct user_namespace *ns,
 			int cap);
+int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
+			     int cap);
 int security_real_capable(struct task_struct *tsk, struct user_namespace *ns,
 			int cap);
 int security_real_capable_noaudit(struct task_struct *tsk,
@@ -1869,6 +1871,11 @@ static inline int security_capable(const struct cred *cred,
 	return cap_capable(cred, ns, cap, SECURITY_CAP_AUDIT);
 }
 
+static inline int security_capable_noaudit(const struct cred *cred,
+					   struct user_namespace *ns, int cap) {
+	return cap_capable(cred, ns, cap, SECURITY_CAP_NOAUDIT);
+}
+
 static inline int security_real_capable(struct task_struct *tsk, struct user_namespace *ns, int cap)
 {
 	int ret;

security/security.c

@@ -160,6 +160,12 @@ int security_capable(const struct cred *cred, struct user_namespace *ns,
 	return security_ops->capable(cred, ns, cap, SECURITY_CAP_AUDIT);
 }
 
+int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
+			     int cap)
+{
+	return security_ops->capable(cred, ns, cap, SECURITY_CAP_NOAUDIT);
+}
+
 int security_real_capable(struct task_struct *tsk, struct user_namespace *ns,
 			  int cap)
 {