linux-kernel - Re: [PATCH 02/36] usercopy: Include offset in overflow report

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Date:   Wed, 10 Jan 2018 13:15:14 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Windsor <dave@...lcore.net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Laura Abbott <labbott@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Dave Kleikamp <dave.kleikamp@...cle.com>,
        Jan Kara <jack@...e.cz>,
        Luis de Bethencourt <luisbg@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Rik van Riel <riel@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 02/36] usercopy: Include offset in overflow report

On Wed, Jan 10, 2018 at 7:25 AM, Christopher Lameter <cl@...ux.com> wrote:
> On Tue, 9 Jan 2018, Kees Cook wrote:
>
>> -static void report_usercopy(unsigned long len, bool to_user, const char *type)
>> +int report_usercopy(const char *name, const char *detail, bool to_user,
>> +                 unsigned long offset, unsigned long len)
>>  {
>> -     pr_emerg("kernel memory %s attempt detected %s '%s' (%lu bytes)\n",
>> +     pr_emerg("kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)\n",
>>               to_user ? "exposure" : "overwrite",
>> -             to_user ? "from" : "to", type ? : "unknown", len);
>> +             to_user ? "from" : "to",
>> +             name ? : "unknown?!",
>> +             detail ? " '" : "", detail ? : "", detail ? "'" : "",
>> +             offset, len);
>>       /*
>>        * For greater effect, it would be nice to do do_group_exit(),
>>        * but BUG() actually hooks all the lock-breaking and per-arch
>>        * Oops code, so that is used here instead.
>>        */
>>       BUG();
>
> Should this be a WARN() or so? Or some configuration that changes
> BUG() behavior? Otherwise

This BUG() is the existing behavior, with the new behavior taking the
WARN() route in a following patch.

>> +
>> +     return -1;
>
> This return code will never be returned.
>
> Why a return code at all? Maybe I will see that in the following patches?

I was trying to simplify the callers, but I agree, the result is
rather ugly. I'll see if I can fix this up.

-Kees

-- 
Kees Cook
Pixel Security