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

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Date:	Thu, 01 May 2014 20:50:46 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Dave Chinner <david@...morbit.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

Dave Chinner <david@...morbit.com> writes:

> 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()


Will update.

>
>> +	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.
>

Ok.

-aneesh

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