`nd' parameter may be null for security_inode_permission()

From: Globe Trekker (globetrekker@private)
Date: Thu Oct 27 2005 - 00:08:20 PDT 

Hi!

I'm implementing a Mandatory Access Control LSM for linux-2.6.12.5.
I have to use security_inode_permission hook to check the permission of 
the access to a file.
I use Extended Attribute to store all MAC attributes of files.
In my mac_inode_permission(), I have to get the MAC attribute of the 
inode, using this:

if ((inode->i_op) && (inode->i_op->getxattr)) {
    error = inode->i_op->getxattr(nd->dentry, POSIX_MAC_XATTR_NAME, 
&mac_xattr, sizeof(posix_mac_xattr));
}

So, you see, I have to use the nd parameter of the 
security_inode_permission() hook. But sometimes this parameter is NULL.  
For now, my mac_inode_permission() just return success if  `nd' is NULL, 
and the MAC mechainism behaves strangely, the MAC control on directories 
just doesn't work.

I tried to get `dentry' from `inode' but found it almost impossible(any 
new idea?). I tried to figure out the situations in which the `nd' 
parameter for security_inode_permission() hook is NULL but found it too 
hard to accomplish.

Any ideas?

Thanks!

Hawk Xu
Beijing

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