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Subject: Re: [PATCH] inode: debugfs_create_dir uses mode permission from
 parent
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     brueckner@linux.vnet.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org
References: <20180427080712.2380-1-tmricht@linux.ibm.com>
 <20180427082737.GA25242@kroah.com>
 <504bade7-7b06-c9d4-e4e2-736b9ee5a313@linux.ibm.com>
 <20180427100600.GB12941@kroah.com>
From:   Thomas-Mich Richter <tmricht@linux.ibm.com>
Organization: IBM LTC
Date:   Fri, 27 Apr 2018 13:30:53 +0200
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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@linux.ibm.com>
>>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.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@s8360047 ~]# 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@s8360047 ~]# 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@s8360047 ~]#

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

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2,52c2,52
< ├── [drwxr-xr-x]  bdi
< │   ├── [drwxr-xr-x]  1:0
< │   ├── [drwxr-xr-x]  1:1
< │   ├── [drwxr-xr-x]  1:10
< │   ├── [drwxr-xr-x]  1:11
< │   ├── [drwxr-xr-x]  1:12
< │   ├── [drwxr-xr-x]  1:13
< │   ├── [drwxr-xr-x]  1:14
< │   ├── [drwxr-xr-x]  1:15
< │   ├── [drwxr-xr-x]  1:2
< │   ├── [drwxr-xr-x]  1:3
< │   ├── [drwxr-xr-x]  1:4
< │   ├── [drwxr-xr-x]  1:5
< │   ├── [drwxr-xr-x]  1:6
< │   ├── [drwxr-xr-x]  1:7
< │   ├── [drwxr-xr-x]  1:8
< │   ├── [drwxr-xr-x]  1:9
< │   └── [drwxr-xr-x]  94:0
< ├── [drwxr-xr-x]  block
< ├── [drwxr-xr-x]  dasd
< │   ├── [drwxr-xr-x]  0.0.e18a
< │   ├── [drwxr-xr-x]  dasda
< │   └── [drwxr-xr-x]  global
< ├── [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]  0.0.f5f2
< ├── [drwxr-xr-x]  s390
< │   └── [drwxr-xr-x]  stsi
< ├── [drwxr-xr-x]  s390dbf
< │   ├── [drwxr-xr-x]  0.0.e18a
< │   ├── [drwxr-xr-x]  cio_crw
< │   ├── [drwxr-xr-x]  cio_msg
< │   ├── [drwxr-xr-x]  cio_trace
< │   ├── [drwxr-xr-x]  dasd
< │   ├── [drwxr-xr-x]  kvm-trace
< │   ├── [drwxr-xr-x]  lgr
< │   ├── [drwxr-xr-x]  qdio_0.0.f5f2
< │   ├── [drwxr-xr-x]  qdio_error
< │   ├── [drwxr-xr-x]  qdio_setup
< │   ├── [drwxr-xr-x]  qeth_card_0.0.f5f0
< │   ├── [drwxr-xr-x]  qeth_control
< │   ├── [drwxr-xr-x]  qeth_msg
< │   ├── [drwxr-xr-x]  qeth_setup
< │   ├── [drwxr-xr-x]  vmcp
< │   └── [drwxr-xr-x]  vmur
---
> ├── [drwx------]  bdi
> │   ├── [drwx------]  1:0
> │   ├── [drwx------]  1:1
> │   ├── [drwx------]  1:10
> │   ├── [drwx------]  1:11
> │   ├── [drwx------]  1:12
> │   ├── [drwx------]  1:13
> │   ├── [drwx------]  1:14
> │   ├── [drwx------]  1:15
> │   ├── [drwx------]  1:2
> │   ├── [drwx------]  1:3
> │   ├── [drwx------]  1:4
> │   ├── [drwx------]  1:5
> │   ├── [drwx------]  1:6
> │   ├── [drwx------]  1:7
> │   ├── [drwx------]  1:8
> │   ├── [drwx------]  1:9
> │   └── [drwx------]  94:0
> ├── [drwx------]  block
> ├── [drwx------]  dasd
> │   ├── [drwx------]  0.0.e18a
> │   ├── [drwx------]  dasda
> │   └── [drwx------]  global
> ├── [drwx------]  device_component
> ├── [drwx------]  extfrag
> ├── [drwx------]  hid
> ├── [drwx------]  kprobes
> ├── [drwx------]  kvm
> ├── [drwx------]  memblock
> ├── [drwx------]  pm_qos
> ├── [drwx------]  qdio
> │   └── [drwx------]  0.0.f5f2
> ├── [drwx------]  s390
> │   └── [drwx------]  stsi
> ├── [drwx------]  s390dbf
> │   ├── [drwx------]  0.0.e18a
> │   ├── [drwx------]  cio_crw
> │   ├── [drwx------]  cio_msg
> │   ├── [drwx------]  cio_trace
> │   ├── [drwx------]  dasd
> │   ├── [drwx------]  kvm-trace
> │   ├── [drwx------]  lgr
> │   ├── [drwx------]  qdio_0.0.f5f2
> │   ├── [drwx------]  qdio_error
> │   ├── [drwx------]  qdio_setup
> │   ├── [drwx------]  qeth_card_0.0.f5f0
> │   ├── [drwx------]  qeth_control
> │   ├── [drwx------]  qeth_msg
> │   ├── [drwx------]  qeth_setup
> │   ├── [drwx------]  vmcp
> │   └── [drwx------]  vmur

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