linux-kernel - Re: [PATCH -V1 08/22] vfs: Add permission flags for setting file attributes

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Date:	Tue, 29 Apr 2014 10:17:23 +1000
From:	Dave Chinner <david@...morbit.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	agruen@...nel.org, bfields@...ldses.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, dhowells@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V1 08/22] vfs: Add permission flags for setting file
 attributes

On Sun, Apr 27, 2014 at 09:44:39PM +0530, Aneesh Kumar K.V wrote:
> From: Andreas Gruenbacher <agruen@...nel.org>
> 
> Some permission models can allow processes to take ownership of a file,
> change the file permissions, and set the file timestamps.  Introduce new
> permission mask flags and check for those permissions in
> inode_change_ok().
> 
> Signed-off-by: Andreas Gruenbacher <agruen@...nel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  fs/attr.c          | 68 ++++++++++++++++++++++++++++++++++++++++++++----------
>  fs/namei.c         |  2 +-
>  include/linux/fs.h |  4 ++++
>  3 files changed, 61 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/attr.c b/fs/attr.c
> index 1d158c972442..e468d4f2dca8 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -16,6 +16,54 @@
>  #include <linux/evm.h>
>  #include <linux/ima.h>
>  
> +static int richacl_change_ok(struct inode *inode, int mask)
> +{

acl_change_ok()

> +	if (!IS_RICHACL(inode))
> +		return -EPERM;
> +
> +	if (inode->i_op->permission)
> +		return inode->i_op->permission(inode, mask);
> +
> +	return check_acl(inode, mask);
> +}
> +
> +static bool inode_uid_change_ok(struct inode *inode, kuid_t ia_uid)
> +{
> +	if (uid_eq(current_fsuid(), inode->i_uid) &&
> +	    uid_eq(ia_uid, inode->i_uid))
> +		return true;
> +	if (uid_eq(current_fsuid(), ia_uid) &&
> +	    richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
> +		return true;
> +	if (capable(CAP_CHOWN))
> +		return true;
> +	return false;
> +}
> +
> +static bool inode_gid_change_ok(struct inode *inode, kgid_t ia_gid)
> +{
> +	int in_group = in_group_p(ia_gid);
> +	if (uid_eq(current_fsuid(), inode->i_uid) &&
> +	    (in_group || gid_eq(ia_gid, inode->i_gid)))
> +		return true;
> +	if (in_group && richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
> +		return true;
> +	if (capable(CAP_CHOWN))
> +		return true;
> +	return false;
> +}
> +
> +static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
> +{
> +	if (uid_eq(current_fsuid(), inode->i_uid))
> +		return true;
> +	if (richacl_change_ok(inode, mask) == 0)
> +		return true;
> +	if (inode_capable(inode, CAP_FOWNER))
> +		return true;
> +	return false;
> +}

Some comments on when and why these need to be used instead of
inode_owner_or_capable() would be useful. I can see people getting
this wrong in future.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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