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Subject: Re: [PATCH] ima: avoid appraise error for hash calc interrupt
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
        Patrick Callaghan <patrickc@linux.ibm.com>,
        linux-integrity@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Sascha Hauer <s.hauer@pengutronix.de>
Date:   Tue, 12 Nov 2019 13:12:24 -0500
In-Reply-To: <c6a57c24-2f30-f252-0f42-8d748ede65af@linux.microsoft.com>
References: <20191111192348.30535-1-patrickc@linux.ibm.com>
         <e3f520ce-a290-206d-8097-b852123357ca@linux.microsoft.com>
         <1573578841.17949.48.camel@linux.ibm.com>
         <c6a57c24-2f30-f252-0f42-8d748ede65af@linux.microsoft.com>
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On Tue, 2019-11-12 at 09:33 -0800, Lakshmi Ramasubramanian wrote:
> On 11/12/2019 9:14 AM, Mimi Zohar wrote:
> 
> > On Mon, 2019-11-11 at 14:29 -0800, Lakshmi Ramasubramanian wrote:
> >> On 11/11/19 11:23 AM, Patrick Callaghan wrote:
> >>
> >>> -		if (rbuf_len == 0)
> >>> +		if (rbuf_len == 0) {	/* unexpected EOF */
> >>> +			rc = -EINVAL;
> >>>    			break;
> >>> +		}
> >>>    		offset += rbuf_len;
> >>
> >> Should there be an additional check to validate that (offset + rbuf_len)
> >> is less than i_size before calling cypto_shash_update (since rbuf_len is
> >> one of the parameters for this call)?
> > 
> > The "while" statement enforces that.
> > 
> > Mimi
> 
> Yes - but that check happens after the call to crypto_shash_update().
> 
> Perhaps integrity_kernel_read() will never return (rbuf_len) that will
>   => violate the check in the "while" statement.
>   => number of bytes read that is greater than the memory allocated for 
> rbuf even in error conditions.
> 
> Just making sure.

integrity_kernel_read() returns an error (< 0) or the number of bytes
read.  The while statement ensures that there is more data to read, so
returning 0 is always an error.

Mimi