linux-kernel - Re: [RESEND][PATCH] ima: Set and clear FMODE_CAN_READ in ima_calc_file

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Message-ID: <20201116174127.GA4578@infradead.org>
Date:   Mon, 16 Nov 2020 17:41:27 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [RESEND][PATCH] ima: Set and clear FMODE_CAN_READ in
 ima_calc_file_hash()

On Mon, Nov 16, 2020 at 09:37:32AM -0800, Linus Torvalds wrote:
> > This discussion seems to be going down the path of requiring an IMA
> > filesystem hook for reading the file, again.  That solution was
> > rejected, not by me.  What is new this time?
> 
> You can't read a non-read-opened file. Not even IMA can.
> 
> So don't do that then.
> 
> IMA is doing something wrong. Why would you ever read a file that can't be read?
> 
> Fix whatever "open" function instead of trying to work around the fact
> that you opened it wrong.

The "issue" with IMA is that it uses security hooks to hook into the
VFS and then wants to read every file that gets opened on a real file
system to "measure" the contents vs a hash stashed away somewhere.
Which has always been rather sketchy.