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

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Date:   Mon, 16 Nov 2020 16:22:02 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.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>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.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 08:52:19AM +0000, Roberto Sassu wrote:
> FMODE_CAN_READ was not set because f_mode does not have
> FMODE_READ. In the patch, I check if the former can be set
> similarly to the way it is done in file_table.c and open.c.
> 
> Is there a better way to read a file when the file was not opened
> for reading and a new file descriptor cannot be created?

You can't open a file not open for reading.  The file system or device
driver might have to prepare read-specific resources in ->open to
support reads.  So what you'll have to do is to open a new instance
of the file that is open for reading.