linux-kernel - Re: IMA & truncate

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Message-ID: <20140506165901.GS18016@ZenIV.linux.org.uk>
Date:	Tue, 6 May 2014 17:59:02 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dmitry Kasatkin <d.kasatkin@...sung.com>
Cc:	linux-security-module <linux-security-module@...r.kernel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: IMA & truncate

On Tue, May 06, 2014 at 04:32:27PM +0300, Dmitry Kasatkin wrote:
> Hi,
> 
> I have discovered one IMA related issue.
> 
> IMA file hash is re-calculate if needed on file close.
> 
> It works with ftruncate(fd, length) syscall, because it operates on
> "opened" file.
> Recalculation is happening on file close.
> 
> truncate(path, length) syscall works with path and no file open/close
> takes place.
> Recalculation does not happen.
> IMA denies file access later.
> 
> It looks like vfs_truncate() should possibly call IMA to recalculate the
> hash.

Who said that it has permissions to read the file?  Reread truncate(2)
manpage; it requires the file to be *writable* for caller, but it doesn't
need it to be readable.
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