netdev - Re: [PATCH bpf] bpf: prevent mmap()'ing read-only maps as writable

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Message-ID: <CAG48ez2HZfjCKG+coVq2k9eE_Hm0rsdQE=O=5nVyKL80QncVZA@mail.gmail.com>
Date:   Thu, 21 May 2020 04:50:32 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf] bpf: prevent mmap()'ing read-only maps as writable

On Tue, May 19, 2020 at 7:38 AM Andrii Nakryiko <andriin@...com> wrote:
> As discussed in [0], it's dangerous to allow mapping BPF map, that's meant to
> be frozen and is read-only on BPF program side, because that allows user-space
> to actually store a writable view to the page even after it is frozen. This is
> exacerbated by BPF verifier making a strong assumption that contents of such
> frozen map will remain unchanged. To prevent this, disallow mapping
> BPF_F_RDONLY_PROG mmap()'able BPF maps as writable, ever.
>
>   [0] https://lore.kernel.org/bpf/CAEf4BzYGWYhXdp6BJ7_=9OQPJxQpgug080MMjdSB72i9R+5c6g@mail.gmail.com/
>
> Suggested-by: Jann Horn <jannh@...gle.com>
> Fixes: fc9702273e2e ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY")
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Reviewed-by: Jann Horn <jannh@...gle.com>