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

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Message-ID: <20200521032931.rs5vbob2gei6ccic@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 20 May 2020 20:29:31 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Andrii Nakryiko <andriin@...com>, 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 Thu, May 21, 2020 at 04:50:32AM +0200, Jann Horn wrote:
> 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>

I fixed trailing white space after 'writable page'
and applied to bpf tree.
Thanks