kernel: Add noaudit variant of ns_capable()

When checking the current cred for a capability in a specific user
namespace, it isn't always desirable to have the LSMs audit the check.
This patch adds a noaudit variant of ns_capable() for when those
situations arise.

The common logic between ns_capable() and the new ns_capable_noaudit()
is moved into a single, shared function to keep duplicated code to a
minimum and ease maintainability.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 00690ff..5f3c63d 100644 (file)
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -206,6 +206,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
                                      struct user_namespace *ns, int cap);
 extern bool capable(int cap);
 extern bool ns_capable(struct user_namespace *ns, int cap);
+extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
 #else
 static inline bool has_capability(struct task_struct *t, int cap)
 {
@@ -233,6 +234,10 @@ static inline bool ns_capable(struct user_namespace *ns, int cap)
 {
        return true;
 }
+static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
+{
+       return true;
+}
 #endif /* CONFIG_MULTIUSER */
 extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
 extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);

diff --git a/kernel/capability.c b/kernel/capability.c
index 45432b5..00411c8 100644 (file)
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -361,6 +361,24 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
        return has_ns_capability_noaudit(t, &init_user_ns, cap);
 }
 
+static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
+{
+       int capable;
+
+       if (unlikely(!cap_valid(cap))) {
+               pr_crit("capable() called with invalid cap=%u\n", cap);
+               BUG();
+       }
+
+       capable = audit ? security_capable(current_cred(), ns, cap) :
+                         security_capable_noaudit(current_cred(), ns, cap);
+       if (capable == 0) {
+               current->flags |= PF_SUPERPRIV;
+               return true;
+       }
+       return false;
+}
+
 /**
  * ns_capable - Determine if the current task has a superior capability in effect
  * @ns:  The usernamespace we want the capability in
@@ -374,19 +392,27 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
  */
 bool ns_capable(struct user_namespace *ns, int cap)
 {
-       if (unlikely(!cap_valid(cap))) {
-               pr_crit("capable() called with invalid cap=%u\n", cap);
-               BUG();
-       }
-
-       if (security_capable(current_cred(), ns, cap) == 0) {
-               current->flags |= PF_SUPERPRIV;
-               return true;
-       }
-       return false;
+       return ns_capable_common(ns, cap, true);
 }
 EXPORT_SYMBOL(ns_capable);
 
+/**
+ * ns_capable_noaudit - Determine if the current task has a superior capability
+ * (unaudited) in effect
+ * @ns:  The usernamespace we want the capability in
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+bool ns_capable_noaudit(struct user_namespace *ns, int cap)
+{
+       return ns_capable_common(ns, cap, false);
+}
+EXPORT_SYMBOL(ns_capable_noaudit);
 
 /**
  * capable - Determine if the current task has a superior capability in effect