linux-kernel - Re: [PATCH 00/23] Removal of binary sysctl support

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Date:	Fri, 20 Nov 2009 07:17:53 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	ebiederm@...ssion.com
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, john.johansen@...onical.com
Subject: Re: [PATCH 00/23] Removal of binary sysctl support

Hello.

Eric W. Biederman wrote:
> > Indeed. TOMOYO and AppArmor need a hint for prepending "/proc" prefix.
> > A simple implementation which adds one bit to task_struct is shown below.
> > In this way, not only the file permission checks inside dentry_open()
> > but also the directory permission checks inside vfs_path_lookup() can be
> > prepended "/proc" prefix. AppArmor might want to prepend "/proc" inside
> > vfs_path_lookup().
> 
> There don't appear to be any security hooks in vfs_path_lookup().
>
OK. Then, AppArmor won't be confused.

> Instead of current->in_sysctl we can just look at the path and see if
> it is the root of the mount chain and if the fs is proc.
> 
> Something like:
> 
> diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
> index 5f2e332..0b55faa 100644
> --- a/security/tomoyo/realpath.c
> +++ b/security/tomoyo/realpath.c
> @@ -108,6 +108,15 @@ int tomoyo_realpath_from_path2(struct path *path, char *newname,
>  		spin_unlock(&dcache_lock);
>  		path_put(&root);
>  		path_put(&ns_root);
> +		/* Prepend "/proc" prefix if using internal proc vfs mount. */
> +		if (!IS_ERR(sp) && (path->mnt->mnt_parent == path->mnt) &&
> +		    (strcmp(path->mnt->mnt_sb->s_type->name, "proc") == 0)) {
> +			sp -= 5;
> +			if (sp >= newname)
> +				memcpy(sp, "/proc", 5);
> +			else
> +				sp = ERR_PTR(-ENOMEM);
> +		}
>  	}
>  	if (IS_ERR(sp))
>  		error = PTR_ERR(sp);

Above patch works. Please proceed. Thank you.

Acked-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

Why not to use path->mnt->mnt_sb->s_magic == PROC_SUPER_MAGIC rather than
strcmp(path->mnt->mnt_sb->s_type->name, "proc") == 0 ?
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