linux-kernel - Re: [PATCH v2 2/2] KVM: s390: Use memdup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdUS2aMd5B2nQOpQFdQGE7EvWMCea+dMzS7R7_yZ4LdONw@mail.gmail.com>
Date:   Mon, 3 Oct 2016 16:00:03 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     kvm@...r.kernel.org, linux-s390 <linux-s390@...r.kernel.org>,
        Christian Bornträger <borntraeger@...ibm.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        David Hildenbrand <dahi@...ux.vnet.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        Walter Harms <wharms@....de>
Subject: Re: [PATCH v2 2/2] KVM: s390: Use memdup_user() rather than
 duplicating code

Hi Markus,

On Mon, Oct 3, 2016 at 3:47 PM, SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:
>>> Did you notice the check "IS_ERR(bp_data)" and the corresponding reaction
>>> in this update suggestion?
>>
>> Yes, but bp_data may still be a valid (as in "not an error") value.
>
> Thanks for your constructive feedback.
>
>> Your commit a1708a2eaded836b ("KVM: s390: Improve determination of sizes in
>> kvm_s390_import_bp_data()") made the code more robust, as kmalloc_array() ha
>>  a builtin overflow check, and will return NULL if overflow is detected.
>> However, commit 0624a8eb82efd58e ("KVM: s390: Use memdup_user() rather than
>> duplicating code") dropped that safety net again.
>
> * How much are you concerned about the shown software evolution around
>   multiplications for memory allocations?

Enough to write my reply ;-)

> * Does there really a probability remain that an inappropriate product
>   would be calculated here (as the situation was before my two update steps
>   for this software module)?

Perhaps not. Hence my "Probably not an issue here, ...".

> * Can it be that you are looking for a variant of a function like "memdup_user"
>   where values can be passed as separate parameters "count" and "size" so that
>   the needed multiplication and corresponding overflow check would be performed
>   together as desired?

If there are enough uses, and people like it, adding memdup_user_array()
may be a good idea...

P.S. Why do your questions make me think of a scientific paper? ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds