linux-kernel - Re: [TOMOYO #8 (2.6.25-mm1) 1/7] Introduce new LSM hooks.

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Date:	Thu, 1 May 2008 01:01:44 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Toshiharu Harada <haradats@...data.co.jp>
Cc:	akpm@...ux-foundation.org, chrisw@...s-sol.org,
	viro@...IV.linux.org.uk, linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kentaro Takeda <takedakn@...data.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [TOMOYO #8 (2.6.25-mm1) 1/7] Introduce new LSM hooks.

* Toshiharu Harada (haradats@...data.co.jp) wrote:
> This patch allows LSM to check permission using "struct vfsmount"
> without passing "struct vfsmount" to VFS helper functions.

This is simply duplicating many of the existing checks.
I don't see how this is an improvement.

> --- mm.orig/fs/namei.c
> +++ mm/fs/namei.c
> @@ -1595,6 +1595,9 @@ int vfs_create(struct inode *dir, struct
>  	error = security_inode_create(dir, dentry, mode);
>  	if (error)
>  		return error;
> +	error = security_path_create(dir, dentry, mode, nd);
> +	if (error)
> +		return error;

Pure duplication (of course adding nameidata, although I think you just
want path).

>  	DQUOT_INIT(dir);
>  	error = dir->i_op->create(dir, dentry, mode, nd);
>  	if (!error)
> @@ -1650,6 +1653,17 @@ int may_open(struct nameidata *nd, int a
	...
	error = vfs_permission(nd, acc_mode);
	if (error)
		return error;
	...
>  			return -EPERM;
>  
>  	/*
> +	 * security_inode_permission() called from vfs_permission()
> +	 * can't know that the file is going to be truncated when
> +	 * open(filename, O_WRONLY | O_TRUNC | O_APPEND) is used.
> +	 * So, this hook checks O_APPEND and O_TRUNC flags as well
> +	 * as MAY_READ and MAY_WRITE flags.
> +	 */
> +	error = security_path_open(nd->path.dentry, nd->path.mnt, flag);
> +	if (error)
> +		return error;

Also duplication.  And why the unique flag handling, you don't seem to
ever check?

> +
> +	/*
>  	 * Ensure there are no outstanding leases on the file.
>  	 */
>  	error = break_lease(inode, flag);
> @@ -2021,7 +2035,12 @@ fail:
>  }
>  EXPORT_SYMBOL_GPL(lookup_create);
>  
> -int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
> +/*
> + * These pre_vfs_*() functions are separated from vfs_*() functions so that
> + * LSM's security_path_*() functions can do DAC checks before MAC checks
> + * without duplicating may_create()/may_delete() functions.
> + */
> +int pre_vfs_mknod(struct inode *dir, struct dentry *dentry, int mode)
>  {
>  	int error = may_create(dir, dentry, NULL);
>  
> @@ -2033,6 +2052,14 @@ int vfs_mknod(struct inode *dir, struct 
>  
>  	if (!dir->i_op || !dir->i_op->mknod)
>  		return -EPERM;
> +	return 0;
> +}
> +
> +int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
> +{
> +	int error = pre_vfs_mknod(dir, dentry, mode);
> +	if (error)
> +		return error;

More duplication, you'll get a call chain like:

sys_mknod
  security_path_mknod
    pre_vfs_mknod
  vfs_mknod
   pre_vfs_mknod
   security_inode_mknod


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