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From:   Lorenz Bauer <lmb@cloudflare.com>
Date:   Tue, 26 Jan 2021 09:36:57 +0000
Message-ID: <CACAyw99bEYWJCSGqfLiJ9Jp5YE1ZsZSiJxb4RFUTwbofipf0dA@mail.gmail.com>
Subject: Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
To:     Bui Quang Minh <minhquangbui99@gmail.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, hawk@kernel.org,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        kpsingh@kernel.org, Jakub Sitnicki <jakub@cloudflare.com>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>
> In 32-bit architecture, the result of sizeof() is a 32-bit integer so
> the expression becomes the multiplication between 2 32-bit integer which
> can potentially leads to integer overflow. As a result,
> bpf_map_area_alloc() allocates less memory than needed.
>
> Fix this by casting 1 operand to u64.

Some quick thoughts:
* Should this have a Fixes tag?
* Seems like there are quite a few similar calls scattered around
(cpumap, etc.). Did you audit these as well?
* I'd prefer a calloc style version of bpf_map_area_alloc although
that might conflict with Fixes tag.

Lorenz

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