linux-kernel - Re: [PATCH 5/6] treewide: use kv[mz]alloc* rather than opencoded variants

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Date:   Fri, 20 Jan 2017 14:41:37 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>, Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Santosh Raspatur <santosh@...lsio.com>,
        Hariprasad S <hariprasad@...lsio.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Yishai Hadas <yishaih@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Sterba <dsterba@...e.com>,
        "Yan, Zheng" <zyan@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 5/6] treewide: use kv[mz]alloc* rather than opencoded
 variants

On 01/12/2017 06:37 PM, Michal Hocko wrote:
> On Thu 12-01-17 09:26:09, Kees Cook wrote:
>> On Thu, Jan 12, 2017 at 7:37 AM, Michal Hocko <mhocko@...nel.org> wrote:
> [...]
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index 4f74511015b8..e6bbb33d2956 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -1126,10 +1126,7 @@ static long kvm_s390_get_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
>>>         if (args->count < 1 || args->count > KVM_S390_SKEYS_MAX)
>>>                 return -EINVAL;
>>>
>>> -       keys = kmalloc_array(args->count, sizeof(uint8_t),
>>> -                            GFP_KERNEL | __GFP_NOWARN);
>>> -       if (!keys)
>>> -               keys = vmalloc(sizeof(uint8_t) * args->count);
>>> +       keys = kvmalloc(args->count * sizeof(uint8_t), GFP_KERNEL);
>>
>> Before doing this conversion, can we add a kvmalloc_array() API? This
>> conversion could allow for the reintroduction of integer overflow
>> flaws. (This particular situation isn't at risk since ->count is
>> checked, but I'd prefer we not create a risky set of examples for
>> using kvmalloc.)
> 
> Well, I am not opposed to kvmalloc_array but I would argue that this
> conversion cannot introduce new overflow issues. The code would have
> to be broken already because even though kmalloc_array checks for the
> overflow but vmalloc fallback doesn't...

Yeah I agree, but if some of the places were really wrong, after the
conversion we won't see them anymore.

> If there is a general interest for this API I can add it.

I think it would be better, yes.