From: Daniel Borkmann <daniel@iogearbox.net>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Jann Horn <jannh@google.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf 1/2] bpf: prevent re-mmap()'ing BPF map as writable for initially r/o mapping
Date: Tue, 14 Apr 2020 21:44:00 +0200 [thread overview]
Message-ID: <900084f0-e435-b2e5-6ef1-06db90ceac94@iogearbox.net> (raw)
In-Reply-To: <CAEf4Bza2=_OM_yxu3FAyf=mRoDmQC6KmFQ-5qKu0bxxX0PkzgQ@mail.gmail.com>
On 4/14/20 8:28 PM, Andrii Nakryiko wrote:
> On Tue, Apr 14, 2020 at 9:58 AM Jann Horn <jannh@google.com> wrote:
>> On Fri, Apr 10, 2020 at 10:26 PM Andrii Nakryiko <andriin@fb.com> wrote:
>>> VM_MAYWRITE flag during initial memory mapping determines if already mmap()'ed
>>> pages can be later remapped as writable ones through mprotect() call. To
>>> prevent user application to rewrite contents of memory-mapped as read-only and
>>> subsequently frozen BPF map, remove VM_MAYWRITE flag completely on initially
>>> read-only mapping.
>>>
>>> Alternatively, we could treat any memory-mapping on unfrozen map as writable
>>> and bump writecnt instead. But there is little legitimate reason to map
>>> BPF map as read-only and then re-mmap() it as writable through mprotect(),
>>> instead of just mmap()'ing it as read/write from the very beginning.
>>>
>>> Also, at the suggestion of Jann Horn, drop unnecessary refcounting in mmap
>>> operations. We can just rely on VMA holding reference to BPF map's file
>>> properly.
>>>
>>> Fixes: fc9702273e2e ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY")
>>> Reported-by: Jann Horn <jannh@google.com>
>>> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>>
>> Reviewed-by: Jann Horn <jannh@google.com>
>>
>> (in the sense that I think this patch is good and correct, but does
>> not fix the entire problem in the bigger picture)
>
> I agree, we'll continue discussion on the other thread, but this
> should be applied as a bug fix anyways.
Applied, thanks!
prev parent reply other threads:[~2020-04-14 19:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-10 20:26 [PATCH v2 bpf 1/2] bpf: prevent re-mmap()'ing BPF map as writable for initially r/o mapping Andrii Nakryiko
2020-04-10 20:26 ` [PATCH v2 bpf 2/2] selftests/bpf: validate frozen map contents stays frozen Andrii Nakryiko
2020-04-14 16:57 ` [PATCH v2 bpf 1/2] bpf: prevent re-mmap()'ing BPF map as writable for initially r/o mapping Jann Horn
2020-04-14 18:28 ` Andrii Nakryiko
2020-04-14 19:44 ` Daniel Borkmann [this message]
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