[PATCH] keys: Permit key expiry time to be set

Add a new keyctl function that allows the expiry time to be set on a key or
removed from a key, provided the caller has attribute modification access.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Alexander Zangerl <az@bond.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/keys.txt

@@ -498,7 +498,7 @@ The keyctl syscall functions are:
      keyring is full, error ENFILE will result.
 
      The link procedure checks the nesting of the keyrings, returning ELOOP if
-     it appears to deep or EDEADLK if the link would introduce a cycle.
+     it appears too deep or EDEADLK if the link would introduce a cycle.
 
 
  (*) Unlink a key or keyring from another keyring:
@@ -628,6 +628,19 @@ The keyctl syscall functions are:
      there is one, otherwise the user default session keyring.
 
 
+ (*) Set the timeout on a key.
+
+	long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
+
+     This sets or clears the timeout on a key. The timeout can be 0 to clear
+     the timeout or a number of seconds to set the expiry time that far into
+     the future.
+
+     The process must have attribute modification access on a key to set its
+     timeout. Timeouts may not be set with this function on negative, revoked
+     or expired keys.
+
+
 ===============
 KERNEL SERVICES
 ===============

include/linux/keyctl.h

@@ -46,5 +46,6 @@
 #define KEYCTL_INSTANTIATE		12	/* instantiate a partially constructed key */
 #define KEYCTL_NEGATE			13	/* negate a partially constructed key */
 #define KEYCTL_SET_REQKEY_KEYRING	14	/* set default request-key keyring */
+#define KEYCTL_SET_TIMEOUT		15	/* set key timeout */
 
 #endif /*  _LINUX_KEYCTL_H */

security/keys/compat.c

@@ -74,6 +74,9 @@ asmlinkage long compat_sys_keyctl(u32 option,
 	case KEYCTL_SET_REQKEY_KEYRING:
 		return keyctl_set_reqkey_keyring(arg2);
 
+	case KEYCTL_SET_TIMEOUT:
+		return keyctl_set_timeout(arg2, arg3);
+
 	default:
 		return -EOPNOTSUPP;
 	}

security/keys/internal.h

@@ -136,6 +136,7 @@ extern long keyctl_instantiate_key(key_serial_t, const void __user *,
 				   size_t, key_serial_t);
 extern long keyctl_negate_key(key_serial_t, unsigned, key_serial_t);
 extern long keyctl_set_reqkey_keyring(int);
+extern long keyctl_set_timeout(key_serial_t, unsigned);
 
 
 /*

security/keys/keyctl.c

@@ -965,6 +965,46 @@ long keyctl_set_reqkey_keyring(int reqkey_defl)
 
 } /* end keyctl_set_reqkey_keyring() */
 
+/*****************************************************************************/
+/*
+ * set or clear the timeout for a key
+ */
+long keyctl_set_timeout(key_serial_t id, unsigned timeout)
+{
+	struct timespec now;
+	struct key *key;
+	key_ref_t key_ref;
+	time_t expiry;
+	long ret;
+
+	key_ref = lookup_user_key(NULL, id, 1, 1, KEY_SETATTR);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
+		goto error;
+	}
+
+	key = key_ref_to_ptr(key_ref);
+
+	/* make the changes with the locks held to prevent races */
+	down_write(&key->sem);
+
+	expiry = 0;
+	if (timeout > 0) {
+		now = current_kernel_time();
+		expiry = now.tv_sec + timeout;
+	}
+
+	key->expiry = expiry;
+
+	up_write(&key->sem);
+	key_put(key);
+
+	ret = 0;
+error:
+	return ret;
+
+} /* end keyctl_set_timeout() */
+
 /*****************************************************************************/
 /*
  * the key control system call
@@ -1038,6 +1078,10 @@ asmlinkage long sys_keyctl(int option, unsigned long arg2, unsigned long arg3,
 	case KEYCTL_SET_REQKEY_KEYRING:
 		return keyctl_set_reqkey_keyring(arg2);
 
+	case KEYCTL_SET_TIMEOUT:
+		return keyctl_set_timeout((key_serial_t) arg2,
+					  (unsigned) arg3);
+
 	default:
 		return -EOPNOTSUPP;
 	}