Re: [PATCH] BTRFS: Establish i_ops before calling d_instantiate

[Al Viro <viro@ZenIV.linux.org.uk>]

On Tue, Dec 06, 2011 at 04:39:50PM -0800, Casey Schaufler wrote:
> From: Casey Schaufler <casey@schaufler-ca.com>
> 
> The Smack LSM hook for security_d_instantiate checks
> the inode's i_op->getxattr value to determine if the
[snip]

> +	inode->i_op = &btrfs_special_inode_operations;
> +
>  	err = btrfs_add_nondir(trans, dir, dentry, inode, 0, index);
>  	if (err)
>  		drop_inode = 1;
>  	else {
> -		inode->i_op = &btrfs_special_inode_operations;
>  		init_special_inode(inode, inode->i_mode, rdev);
>  		btrfs_update_inode(trans, root, inode);

To hell with LSM, there are much stronger reasons why d_instantiate() on
a half-baked inode is wrong.  As soon as you've done it somebody can
come and look that dentry up.

IOW, the bug is real, but this patch is not enough - in particular, ->create()
part is simply wrong.  We need to set ->a_ops before some joker comes and
tries to open it, at the very least...