netdev - Re: [PATCH bpf] bpf: change size to u64 for bpf_map_{area_alloc,charge

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Date:   Tue, 29 Oct 2019 17:16:24 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf] bpf: change size to u64 for bpf_map_{area_alloc,charge_init}()

On Tue, 29 Oct 2019 at 17:12, Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Tue, 29 Oct 2019 16:43:07 +0100, Björn Töpel wrote:
> > From: Björn Töpel <bjorn.topel@...el.com>
> >
> > The functions bpf_map_area_alloc() and bpf_map_charge_init() prior
> > this commit passed the size parameter as size_t. In this commit this
> > is changed to u64.
> >
> > All users of these functions avoid size_t overflows on 32-bit systems,
> > by explicitly using u64 when calculating the allocation size and
> > memory charge cost. However, since the result was narrowed by the
> > size_t when passing size and cost to the functions, the overflow
> > handling was in vain.
> >
> > Instead of changing all call sites to size_t and handle overflow at
> > the call site, the parameter is changed to u64 and checked in the
> > functions above.
> >
> > Fixes: d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
> > Fixes: c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()")
> > Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
>
> Okay, I guess that's the smallest change we can make here.
>
> I'd prefer we went the way of using the standard overflow handling the
> kernel has, rather than proliferating this u64 + U32_MAX comparison
> stuff. But it's hard to argue with the patch length in light of the
> necessary backports..
>

I agree with you, but this is a start, and then maps can gradually
move over to standard overflow handling.

> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>