linux-kernel - Re: [patch] unprivileged mounts update

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Date:	Fri, 27 Apr 2007 09:01:44 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Miklos Szeredi <miklos@...redi.hu>
cc:	ebiederm@...ssion.com, akpm@...ux-foundation.org, serue@...ibm.com,
	viro@....linux.org.uk, linuxram@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, hpa@...or.com
Subject: Re: [patch] unprivileged mounts update


On Apr 26 2007 22:27, Miklos Szeredi wrote:
>> On Apr 25 2007 11:21, Eric W. Biederman wrote:
>> >>
>> >> Why did we want to use fsuid, exactly?
>> >
>> >- Because ruid is completely the wrong thing we want mounts owned
>> >  by whomever's permissions we are using to perform the mount.
>> 
>> Think nfs. I access some nfs file as an unprivileged user. knfsd, by
>> nature, would run as euid=0, uid=0, but it needs fsuid=jengelh for
>> most permission logic to work as expected.
>
>I don't think knfsd will ever want to call mount(2).

I was actually out at something different...

        /* Make sure a caller can chown. */
        if ((ia_valid & ATTR_UID) &&
            (current->fsuid != inode->i_uid ||
             attr->ia_uid != inode->i_uid) && !capable(CAP_CHOWN))
                goto error;

for example. Using current->[e]uid would not make sense here.

>But yeah, I've been convinced, that using fsuid is the right thing to
>do.

Jan
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