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

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Message-Id: <504bade7-7b06-c9d4-e4e2-736b9ee5a313@linux.ibm.com>
Date:   Fri, 27 Apr 2018 11:14:26 +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 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.


-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
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