staging: lustre: hsm: permission checks for HSM ioctl operations

In the LL_IOC_HSM_CT_START case of ll_dir_ioctl() require
CAP_SYS_ADMIN, since the local handler for this ioctl may modify the
global KUC table.
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3866
Reviewed-on: http://review.whamcloud.com/7565Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/dir.c

@@ -1843,6 +1843,9 @@ static long ll_dir_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return rc;
 	}
 	case LL_IOC_HSM_CT_START:
+		if (!capable(CFS_CAP_SYS_ADMIN))
+			return -EPERM;
+
 		rc = copy_and_ioctl(cmd, sbi->ll_md_exp, (void __user *)arg,
 				    sizeof(struct lustre_kernelcomm));
 		return rc;