KEYS: Add a new keyctl op to reject a key with a specified error code

Add a new keyctl op to reject a key with a specified error code.  This works
much the same as negating a key, and so keyctl_negate_key() is made a special
case of keyctl_reject_key().  The difference is that keyctl_negate_key()
selects ENOKEY as the error to be reported.

Typically the key would be rejected with EKEYEXPIRED, EKEYREVOKED or
EKEYREJECTED, but this is not mandatory.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 38 insertions, 2 deletions

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 31a0fd8189f..0d7b1946ff9 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1013,12 +1013,42 @@ error:
  */
 long keyctl_negate_key(key_serial_t id, unsigned timeout, key_serial_t ringid)
 {
+        return keyctl_reject_key(id, timeout, ENOKEY, ringid);
+}
+
+/*
+ * Negatively instantiate the key with the given timeout (in seconds) and error
+ * code and link the key into the destination keyring if one is given.
+ *
+ * The caller must have the appropriate instantiation permit set for this to
+ * work (see keyctl_assume_authority).  No other permissions are required.
+ *
+ * The key and any links to the key will be automatically garbage collected
+ * after the timeout expires.
+ *
+ * Negative keys are used to rate limit repeated request_key() calls by causing
+ * them to return the specified error code until the negative key expires.
+ *
+ * If successful, 0 will be returned.
+ */
+long keyctl_reject_key(key_serial_t id, unsigned timeout, unsigned error,
+                       key_serial_t ringid)
+{
         const struct cred *cred = current_cred();
         struct request_key_auth *rka;
         struct key *instkey, *dest_keyring;
         long ret;
 
-        kenter("%d,%u,%d", id, timeout, ringid);
+        kenter("%d,%u,%u,%d", id, timeout, error, ringid);
+
+        /* must be a valid error code and mustn't be a kernel special */
+        if (error <= 0 ||
+            error >= MAX_ERRNO ||
+            error == ERESTARTSYS ||
+            error == ERESTARTNOINTR ||
+            error == ERESTARTNOHAND ||
+            error == ERESTART_RESTARTBLOCK)
+                return -EINVAL;
 
         /* the appropriate instantiation authorisation key must have been
          * assumed before calling this */
@@ -1038,7 +1068,7 @@ long keyctl_negate_key(key_serial_t id, unsigned timeout, key_serial_t ringid)
                 goto error;
 
         /* instantiate the key and link it into a keyring */
-        ret = key_negate_and_link(rka->target_key, timeout,
+        ret = key_reject_and_link(rka->target_key, timeout, error,
                                   dest_keyring, instkey);
 
         key_put(dest_keyring);
@@ -1492,6 +1522,12 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
         case KEYCTL_SESSION_TO_PARENT:
                 return keyctl_session_to_parent();
 
+        case KEYCTL_REJECT:
+                return keyctl_reject_key((key_serial_t) arg2,
+                                         (unsigned) arg3,
+                                         (unsigned) arg4,
+                                         (key_serial_t) arg5);
+
         default:
                 return -EOPNOTSUPP;
         }