linux-kernel - Re: [PATCH] inode: debugfs_create_dir uses mode permission from parent

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Date:   Fri, 27 Apr 2018 13:30:53 +0200
From:   Thomas-Mich Richter <tmricht@...ux.ibm.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] inode: debugfs_create_dir uses mode permission from
 parent

On 04/27/2018 12:06 PM, Greg KH wrote:
> On Fri, Apr 27, 2018 at 11:14:26AM +0200, Thomas-Mich Richter wrote:
>> On 04/27/2018 10:27 AM, Greg KH wrote:
>>> On Fri, Apr 27, 2018 at 10:07:12AM +0200, Thomas Richter wrote:
>>>> Currently function debugfs_create_dir() creates a new
>>>> directory in the debugfs (usually mounted /sys/kernel/debug)
>>>> with permission rwxr-xr-x. This is hard coded.
>>>>
>>>> Change this to use the parent directory permission.
>>>>
>>>> Fixes: edac65eaf8d5c ("debugfs: take mode-dependent parts of debugfs_get_inode() into callers")
>>>> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> ---
>>>>  fs/debugfs/inode.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
>>>> index 13b01351dd1c..80618330d86a 100644
>>>> --- a/fs/debugfs/inode.c
>>>> +++ b/fs/debugfs/inode.c
>>>> @@ -512,7 +512,10 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
>>>>  	if (unlikely(!inode))
>>>>  		return failed_creating(dentry);
>>>>  
>>>> -	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
>>>> +	if(!parent)
>>>> +		parent = debugfs_mount->mnt_root;
>>>> +	inode->i_mode = S_IFDIR | (d_inode(parent)->i_mode
>>>> +				   & (S_IRWXU | S_IRWXG));
>>>>  	inode->i_op = &simple_dir_inode_operations;
>>>>  	inode->i_fop = &simple_dir_operations;
>>>>  
>>>
>>> This looks ok, but is it going to change the permissions of existing
>>> stuff in ways that might breaks things, right?
>>
>> Right, but debugfs is usually mounted on /sys/kernel/debug with
>> permissions rwx to root owner. It can be changed after the mount, of course.
>> Unless this is done, the directory permissions for /sys/kernel/debug
>> will stop any descend regardless  of the subdirectory permissions.
>>
>>>
>>> Have you done a before/after comparison?
>>
>> I have tested this patch on my Linux 4.17.0rc2 kernel on s390.
>> That worked well, I have not tested other systems.
> 
> What do you mean by "worked well"?  What were the full tree differences
> between before and after?  You should be able to get this by using:
> 	tree -dp /sys/kernel/debug/
> and then doing a diff on the two files.
> 
> thanks,
> 
> greg k-h
> 

Ok, this is the tree output

Before the patch:
root@...60047 ~]# tree -dp -L 1 /sys/kernel/debug/ 
/sys/kernel/debug/
├── [drwxr-xr-x]  bdi
├── [drwxr-xr-x]  block
├── [drwxr-xr-x]  dasd
├── [drwxr-xr-x]  device_component
├── [drwxr-xr-x]  extfrag
├── [drwxr-xr-x]  hid
├── [drwxr-xr-x]  kprobes
├── [drwxr-xr-x]  kvm
├── [drwxr-xr-x]  memblock
├── [drwxr-xr-x]  pm_qos
├── [drwxr-xr-x]  qdio
├── [drwxr-xr-x]  s390
├── [drwxr-xr-x]  s390dbf
└── [drwx------]  tracing

14 directories

After the patch:
[root@...60047 ~]# tree -dp -L 1 /sys/kernel/debug/
sys/kernel/debug/
├── [drwx------]  bdi
├── [drwx------]  block
├── [drwx------]  dasd
├── [drwx------]  device_component
├── [drwx------]  extfrag
├── [drwx------]  hid
├── [drwx------]  kprobes
├── [drwx------]  kvm
├── [drwx------]  memblock
├── [drwx------]  pm_qos
├── [drwx------]  qdio
├── [drwx------]  s390
├── [drwx------]  s390dbf
└── [drwx------]  tracing

14 directories
[root@...60047 ~]#

I attached the diff of the full tree before and after the patch.


-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz 
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

View attachment "treefull.diff" of type "text/x-patch" (3981 bytes)