From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/
 directory v12
Date: Wed, 14 Sep 2011 20:00:19 +0400
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Cc: Pavel Machek <pavel@ucw.cz>, Andrew Morton <akpm00@gmail.com>,
	linux-kernel@vger.kernel.org, containers@lists.osdl.org,
	linux-fsdevel@vger.kernel.org,
	Kirill Shutemov <kirill@shutemov.name>,
	Pavel Emelyanov <xemul@parallels.com>,
	James Bottomley <jbottomley@parallels.com>,
	Nathan Lynch <ntl@pobox.com>, Zan Lynx <zlynx@acm.org>,
	Daniel Lezcano <dlezcano@fr.ibm.com>,
	Tejun Heo <tj@kernel.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Al Viro <viro@ZenIV.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>
To: Vasiliy Kulikov <segoon@openwall.com>
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On Wed, Sep 14, 2011 at 06:48:41PM +0400, Vasiliy Kulikov wrote:
...
> 
> Actually now I see the difference between having something mapped and
> having an _fd_ of this something.
> 
> Relevant code:
> 
> +static struct dentry *
> +proc_map_files_instantiate(struct inode *dir, struct dentry *dentry,
> +              struct task_struct *task, const void *ptr)
> +{
> ...
> +   inode->i_mode = S_IFLNK;
> +
> +   if (file->f_mode & FMODE_READ)
> +       inode->i_mode |= S_IRUSR | S_IXUSR;
> +   if (file->f_mode & FMODE_WRITE)
> +       inode->i_mode |= S_IWUSR | S_IXUSR;
> 
> 
> If you have a write mmap area, but no fd, you may not trunc a file; with
> map_files/ you may get an fd and ftrunc it.
> 

This stands for anonymous memory, and if you have enough rights to
access the task this ftruncate is the last problem (since having ptrace
access to the task I _aready_ can trash various stuff inside, i dont need
even bother to look into map_files/ or whatever). So I don't see how
ftruncate migh harm you here?

	Cyrill