autofs: make dev ioctl version and ismountpoint user accessible

Some of the autofs miscellaneous device ioctls need to be accessable to
user space applications without CAP_SYS_ADMIN to get information about
autofs mounts.

Link: http://lkml.kernel.org/r/150216642517.11652.2338933266137331637.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Colin Walters <walters@redhat.com>
Cc: Ondrej Holy <oholy@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/dev-ioctl.c

@@ -628,10 +628,6 @@ static int _autofs_dev_ioctl(unsigned int command,
 	ioctl_fn fn = NULL;
 	int err = 0;
 
-	/* only root can play with this */
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
 	cmd_first = _IOC_NR(AUTOFS_DEV_IOCTL_IOC_FIRST);
 	cmd = _IOC_NR(command);
 
@@ -640,6 +636,14 @@ static int _autofs_dev_ioctl(unsigned int command,
 		return -ENOTTY;
 	}
 
+	/* Only root can use ioctls other than AUTOFS_DEV_IOCTL_VERSION_CMD
+	 * and AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD
+	 */
+	if (cmd != AUTOFS_DEV_IOCTL_VERSION_CMD &&
+	    cmd != AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD &&
+	    !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	/* Copy the parameters into kernel space. */
 	param = copy_dev_ioctl(user);
 	if (IS_ERR(param))

include/uapi/linux/auto_dev-ioctl.h

@@ -16,7 +16,7 @@
 #define AUTOFS_DEVICE_NAME		"autofs"
 
 #define AUTOFS_DEV_IOCTL_VERSION_MAJOR	1
-#define AUTOFS_DEV_IOCTL_VERSION_MINOR	0
+#define AUTOFS_DEV_IOCTL_VERSION_MINOR	1
 
 #define AUTOFS_DEV_IOCTL_SIZE		sizeof(struct autofs_dev_ioctl)