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From: Kees Cook <keescook@chromium.org>
Date: Wed, 10 Jan 2018 13:15:14 -0800
Message-ID: <CAGXu5jLdtLQhkcujTjMwKCwbV6kVb7-2mqz4ki-B9NtPTrDQ9A@mail.gmail.com>
Subject: Re: [PATCH 02/36] usercopy: Include offset in overflow report
To: Christopher Lameter <cl@linux.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Windsor <dave@nullcore.net>,
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        Andy Lutomirski <luto@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        "David S. Miller" <davem@davemloft.net>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Christoffer Dall <christoffer.dall@linaro.org>,
        Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jan Kara <jack@suse.cz>,
        Luis de Bethencourt <luisbg@kernel.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Rik van Riel <riel@redhat.com>,
        Matthew Garrett <mjg59@google.com>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
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        Network Development <netdev@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        kernel-hardening@lists.openwall.com
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Sender: linux-kernel-owner@vger.kernel.org

On Wed, Jan 10, 2018 at 7:25 AM, Christopher Lameter <cl@linux.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