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

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Message-ID: <939ee428816825b5b28641d6e09b5e75b4172917.camel@linux.ibm.com>
Date:   Wed, 18 Nov 2020 13:28:38 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     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 Tue, 2020-11-17 at 15:36 -0800, Linus Torvalds wrote:
> Another alternative is to change the policy and say "any write-only
> open gets turned into a read-write open".
> 
> But it needs to be done at *OPEN* time, not randomly afterwards by
> just lying to the 'struct file'.

The ima_file_check hook is at open, but it is immediately after
vfs_open().   Only after the file is opened can we determine if the
file is in policy.  If the file was originally opened without read
permission, a new file instance (dentry_open) with read permission is
opened.  Would limiting opening a new file instance with read
permission to just the ima_file_check hook be acceptable?

thanks,

Mimi