linux-kernel - Re: [PATCH RFC 09/12] userns: Convert ocfs2 to use kuid and kgid where appropriate

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Message-ID: <20121121195940.GO2822@localhost>
Date:	Wed, 21 Nov 2012 11:59:41 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-fsdevel@...r.kernel.org,
	Linux Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org, "Serge E. Hallyn" <serge@...lyn.com>,
	Mark Fasheh <mfasheh@...e.com>
Subject: Re: [PATCH RFC 09/12] userns: Convert ocfs2 to use kuid and kgid
 where appropriate

On Tue, Nov 20, 2012 at 04:43:37AM -0800, Eric W. Biederman wrote:
> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
> index 260b162..8a40457 100644
> --- a/fs/ocfs2/acl.c
> +++ b/fs/ocfs2/acl.c
> @@ -65,7 +65,20 @@ static struct posix_acl *ocfs2_acl_from_xattr(const void *value, size_t size)
>  
>  		acl->a_entries[n].e_tag  = le16_to_cpu(entry->e_tag);
>  		acl->a_entries[n].e_perm = le16_to_cpu(entry->e_perm);
> -		acl->a_entries[n].e_id   = le32_to_cpu(entry->e_id);
> +		switch(acl->a_entries[n].e_tag) {
> +		case ACL_USER:
> +			acl->a_entries[n].e_uid =
> +				make_kuid(&init_user_ns,
> +					  le32_to_cpu(entry->e_id));
> +			break;

Stupid question: do you consider disjoint namespaces on multiple
machines to be a problem?  Remember that ocfs2 is a cluster filesystem.
If I have uid 100 on machine A in the default namespace, and then I
mount the filesystem on machine B with uid 100 in a different namespace,
what happens?  I presume that both can access as the same nominal uid,
and configuring this correctly is left as an exercise to the namespace
administrator?

> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 4f7795f..f99af1c 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -2045,8 +2045,8 @@ static void __ocfs2_stuff_meta_lvb(struct inode *inode)
>  	lvb->lvb_version   = OCFS2_LVB_VERSION;
>  	lvb->lvb_isize	   = cpu_to_be64(i_size_read(inode));
>  	lvb->lvb_iclusters = cpu_to_be32(oi->ip_clusters);
> -	lvb->lvb_iuid      = cpu_to_be32(inode->i_uid);
> -	lvb->lvb_igid      = cpu_to_be32(inode->i_gid);
> +	lvb->lvb_iuid      = cpu_to_be32(i_uid_read(inode));
> +	lvb->lvb_igid      = cpu_to_be32(i_gid_read(inode));

	I have the reverse question here.  Are we guaranteed that the
on-disk uid/gid will not change regardless of the namespace?  That is,
if I create a file on machine A in init_user_ns as uid 100, then access
it over on machine B in some other namespace with a user-visible uid of
100, will the wire be passing 100 in both directions?  This absolutely
must be true for the cluster communication to work.

Joel


-- 

Life's Little Instruction Book #80

	"Slow dance"

			http://www.jlbec.org/
			jlbec@...lplan.org
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