linux-kernel - Re: [PATCH 12/13] ovl: switch to __inode

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Date:	Wed, 15 Aug 2012 10:34:58 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Andy Whitcroft <apw@...onical.com>
CC:	Miklos Szeredi <miklos@...redi.hu>, viro@...IV.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, nbd@...nwrt.org, neilb@...e.de,
	hramrach@...trum.cz, jordipujolp@...il.com, ezk@....cs.sunysb.edu,
	ricwheeler@...il.com, dhowells@...hat.com, hpj@...la.net,
	sedat.dilek@...glemail.com, penberg@...nel.org,
	goran.cetusic@...il.com, romain@...bokech.com, mszeredi@...e.cz
Subject: Re: [PATCH 12/13] ovl: switch to __inode_permission()

On 8/15/2012 10:07 AM, Andy Whitcroft wrote:
> On Wed, Aug 15, 2012 at 09:59:51AM -0700, Casey Schaufler wrote:
>> On 8/15/2012 8:48 AM, Miklos Szeredi wrote:
>>> From: Andy Whitcroft <apw@...onical.com>
>>>
>>> When checking permissions on an overlayfs inode we do not take into
>>> account either device cgroup restrictions nor security permissions.
>>> This allows a user to mount an overlayfs layer over a restricted device
>>> directory and by pass those permissions to open otherwise restricted
>>> files.
>> Why is this a good idea? Either you're not including enough context
>> about the conditions under which this can occur, or you're suggesting
>> the introduction of a trivial mechanism for bypassing all file access
>> controls. This does not seem right.
> It is stating that the unprotected case is how things was before this
> patch switches us over to __inode_permisssions.  The patch is closing
> the hole indicated.

Well, that's good then. Carry on.

>
> -apw
>>> Switch over to __inode_permissions.
>>>
>>> Signed-off-by: Andy Whitcroft <apw@...onical.com>
>>> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
>>> ---
>>>  fs/overlayfs/inode.c |   12 +-----------
>>>  1 files changed, 1 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>> index e854720..f3a534f 100644
>>> --- a/fs/overlayfs/inode.c
>>> +++ b/fs/overlayfs/inode.c
>>> @@ -100,19 +100,9 @@ int ovl_permission(struct inode *inode, int mask)
>>>  		if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
>>>  		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
>>>  			goto out_dput;
>>> -
>>> -		/*
>>> -		 * Nobody gets write access to an immutable file.
>>> -		 */
>>> -		err = -EACCES;
>>> -		if (IS_IMMUTABLE(realinode))
>>> -			goto out_dput;
>>>  	}
>>>  
>>> -	if (realinode->i_op->permission)
>>> -		err = realinode->i_op->permission(realinode, mask);
>>> -	else
>>> -		err = generic_permission(realinode, mask);
>>> +	err = __inode_permission(realinode, mask);
>>>  out_dput:
>>>  	dput(alias);
>>>  	return err;
> --
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