linux-kernel - Re: [PATCH] keys/encrypted: Fix two crypto-on-the-stack bugs

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Message-ID: <CALCETrVPnrXVcapWezAw+AwEpcyTybKUpAO4YqVDk+e1yBUoUw@mail.gmail.com>
Date:   Mon, 12 Dec 2016 16:32:03 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>, keyrings@...r.kernel.org,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH] keys/encrypted: Fix two crypto-on-the-stack bugs

On Mon, Dec 12, 2016 at 2:28 PM, David Howells <dhowells@...hat.com> wrote:
> Andy Lutomirski <luto@...nel.org> wrote:
>
>> +static const char zero_pad[16] = {0};
>
> Isn't there a global page of zeros or something that we can share?  Also, you
> shouldn't explicitly initialise it so that it stays in .bss.

This is a double-edged sword.  It seems that omitting the
initialization causes it to go in .bss, which isn't read only.  I have
no idea why initializing make a difference at all -- the IMO sensible
behavior would be to put it in .rodata as NOBITS either way.

But I'll use empty_zero_page.

>
>> -     sg_set_buf(&sg_out[1], pad, sizeof pad);
>> +     sg_set_buf(&sg_out[1], zero_pad, sizeof zero_pad);
>
> Can you put brackets on the sizeof?

Will do for v2.