Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757587AbaD2WY6 (ORCPT ); Tue, 29 Apr 2014 18:24:58 -0400 Received: from mail.siteground.com ([67.19.240.234]:57700 "EHLO mail.siteground.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751644AbaD2WY4 (ORCPT ); Tue, 29 Apr 2014 18:24:56 -0400 Message-ID: <536026B3.1020905@1h.com> Date: Wed, 30 Apr 2014 01:24:51 +0300 From: Marian Marinov Organization: 1H Ltd. User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Serge Hallyn CC: "Theodore Ts'o" , containers@lists.linux-foundation.org, LXC development mailing-list , "linux-kernel@vger.kernel.org" Subject: Re: ioctl CAP_LINUX_IMMUTABLE is checked in the wrong namespace References: <535FADDA.2070803@1h.com> <20140429183534.GB19325@thunk.org> <20140429185251.GA27969@ubuntumail> <53601E5B.5050004@1h.com> <20140429220234.GC28410@ubuntumail> In-Reply-To: <20140429220234.GC28410@ubuntumail> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - mail.siteground.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - 1h.com X-Get-Message-Sender-Via: mail.siteground.com: none X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/30/2014 01:02 AM, Serge Hallyn wrote: > Quoting Marian Marinov (mm@1h.com): >> On 04/29/2014 09:52 PM, Serge Hallyn wrote: >>> Quoting Theodore Ts'o (tytso@mit.edu): >>>> On Tue, Apr 29, 2014 at 04:49:14PM +0300, Marian Marinov wrote: >>>>> >>>>> I'm proposing a fix to this, by replacing the capable(CAP_LINUX_IMMUTABLE) >>>>> check with ns_capable(current_cred()->user_ns, CAP_LINUX_IMMUTABLE). >>>> >>>> Um, wouldn't it be better to simply fix the capable() function? >>>> >>>> /** >>>> * capable - Determine if the current task has a superior capability in effect >>>> * @cap: The capability to be tested for >>>> * >>>> * Return true if the current task has the given superior capability currently >>>> * available for use, false if not. >>>> * >>>> * This sets PF_SUPERPRIV on the task if the capability is available on the >>>> * assumption that it's about to be used. >>>> */ >>>> bool capable(int cap) >>>> { >>>> return ns_capable(&init_user_ns, cap); >>>> } >>>> EXPORT_SYMBOL(capable); >>>> >>>> The documentation states that it is for "the current task", and I >>>> can't imagine any use case, where user namespaces are in effect, where >>>> using init_user_ns would ever make sense. >>> >>> the init_user_ns represents the user_ns owning the object, not the >>> subject. >>> >>> The patch by Marian is wrong. Anyone can do 'clone(CLONE_NEWUSER)', >>> setuid(0), execve, and end up satisfying 'ns_capable(current_cred()->userns, >>> CAP_SYS_IMMUTABLE)' by definition. >>> >>> So NACK to that particular patch. I'm not sure, but IIUC it should be >>> safe to check against the userns owning the inode? >>> >> >> So what you are proposing is to replace 'ns_capable(current_cred()->userns, CAP_SYS_IMMUTABLE)' with >> 'inode_capable(inode, CAP_SYS_IMMUTABLE)' ? >> >> I agree that this is more sane. > > Right, and I think the two operations you're looking at seem sane > to allow. If you are ok with this patch, I will fix all file systems and send patches. Signed-off-by: Marian Marinov --- fs/ext4/ioctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c index d011b69..9418634 100644 --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -265,7 +265,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) * This test looks nicer. Thanks to Pauline Middelink */ if ((flags ^ oldflags) & (EXT4_APPEND_FL | EXT4_IMMUTABLE_FL)) { - if (!capable(CAP_LINUX_IMMUTABLE)) + if (!inode_capable(inode, CAP_LINUX_IMMUTABLE)) goto flags_out; } --- 1.8.4 Marian > > thanks, > -serge > -- Marian Marinov Founder & CEO of 1H Ltd. Jabber/GTalk: hackman@jabber.org ICQ: 7556201 Mobile: +359 886 660 270 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/