From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752227AbbDPTbb (ORCPT ); Thu, 16 Apr 2015 15:31:31 -0400 Received: from mail-vn0-f43.google.com ([209.85.216.43]:40632 "EHLO mail-vn0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751455AbbDPTbW (ORCPT ); Thu, 16 Apr 2015 15:31:22 -0400 MIME-Version: 1.0 In-Reply-To: <20150416150847.GA16917@azat> References: <552FA066.3010905@huawei.com> <20150416150847.GA16917@azat> Date: Thu, 16 Apr 2015 21:31:21 +0200 Message-ID: Subject: Re: [PATCH] fs/sync.c : Add CAP_SYS_ADMIN checking before sync From: Richard Weinberger To: Azat Khuzhin Cc: Wuqixuan , Al Viro , linux-fsdevel , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 16, 2015 at 5:08 PM, Azat Khuzhin wrote: > On Thu, Apr 16, 2015 at 07:43:34PM +0800, Wuqixuan wrote: >> The process, supposed in one container, can't flush the metadata >> and data of the all host's partitions without CAP_SYS_ADMIN >> capability, like sys_mount is doing. The checking will prevent some >> vicious programs impacting IO sequnces of those partitions, >> particularly, the ones which can't be accessed in the container. >> >> Signed-off-by: Last Wu >> --- >> fs/sync.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/fs/sync.c b/fs/sync.c >> index fbc98ee..9f07909 100644 >> --- a/fs/sync.c >> +++ b/fs/sync.c >> @@ -103,6 +103,9 @@ SYSCALL_DEFINE0(sync) >> { >> int nowait = 0, wait = 1; >> >> + if (!capable(CAP_SYS_ADMIN)) >> + return -EPERM; > > So after this patch I can't call sync as a regular user? (even without > containers). > But nothing in sync(2) says about special permissions for this. Yeah, this solution will break userspace. A much more generic solution would be to wait for cgroup aware writeback[1]. As temporary hack you can check whether the calling process is in the initial pid namesapce to detect a container calling sync(2)... [1] https://lwn.net/Articles/628631/ -- Thanks, //richard