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

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Date:   Fri, 27 Apr 2018 12:06:00 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Thomas-Mich Richter <tmricht@...ux.ibm.com>
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 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