From: Florian Westphal <fw@strlen.de>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Florian Westphal <fw@strlen.de>,
Lorenzo Bianconi <lorenzo@kernel.org>,
bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org,
daniel@iogearbox.net, andrii@kernel.org, davem@davemloft.net,
kuba@kernel.org, edumazet@google.com, pabeni@redhat.com,
pablo@netfilter.org, netfilter-devel@vger.kernel.org,
lorenzo.bianconi@redhat.com, brouer@redhat.com, toke@redhat.com,
yhs@fb.com
Subject: Re: [PATCH v4 bpf-next 06/14] bpf: Whitelist some fields in nf_conn for BPF_WRITE
Date: Fri, 27 May 2022 14:02:17 +0200 [thread overview]
Message-ID: <20220527120217.GG7680@breakpoint.cc> (raw)
In-Reply-To: <20220527113343.h3q5zmkmqm7fev7r@apollo.legion>
Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
> On Fri, May 27, 2022 at 03:15:58AM IST, Florian Westphal wrote:
> > Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> > > From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > >
> > > Since we want to allow user to set some fields in nf_conn after it is
> > > allocated but before it is inserted, we can permit BPF_WRITE for normal
> > > nf_conn, and then mark return value as read only on insert, preventing
> > > further BPF_WRITE. This way, nf_conn can be written to using normal
> > > BPF instructions after allocation, but not after insertion.
> > >
> > > Note that we special nf_conn a bit here, inside the btf_struct_access
> > > callback for XDP and TC programs. Since this is the only struct for
> > > these programs requiring such adjustments, making this mechanism
> > > more generic has been left as an exercise for a future patch adding
> > > custom callbacks for more structs.
> >
> > Are you sure this is safe?
> > As far as I can see this allows nf_conn->status = ~0ul.
> > I'm fairly sure this isn't a good idea, see nf_ct_delete() for example.
>
> This only allows writing to an allocated but not yet inserted nf_conn. The idea
> was that insert checks whether ct->status only has permitted bits set before
> making the entry visible, and then we make nf_conn pointer read only, however
> the runtime check seems to be missing right now in patch 12; something to fix in
> v5. With that sorted, would it be fine?
Its fragile, e.g. what if I set TEMPLATE bit? If refcount goes down to
0, object is released via kfree() instead of kmem_cache_free.
What if I clear SNAT_DONE bit? Would it leave the (freed) entry on the
bysource hash list (see nf_nat_core.c)?
Or is there some magic that prevents this from happening? I have no
idea how processing pipeline looks like...
next prev parent reply other threads:[~2022-05-27 12:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-26 21:34 [PATCH v4 bpf-next 00/14] net: netfilter: add kfunc helper to update ct timeout Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 01/14] bpf: Add support for forcing kfunc args to be referenced Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 02/14] bpf: Print multiple type flags in verifier log Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 03/14] bpf: Support rdonly PTR_TO_BTF_ID for pointer to const return value Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 04/14] bpf: Support storing rdonly PTR_TO_BTF_ID in BPF maps Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 05/14] bpf: Support passing rdonly PTR_TO_BTF_ID to kfunc Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 06/14] bpf: Whitelist some fields in nf_conn for BPF_WRITE Lorenzo Bianconi
2022-05-26 21:45 ` Florian Westphal
2022-05-27 11:36 ` Kumar Kartikeya Dwivedi
2022-05-27 12:02 ` Florian Westphal [this message]
2022-05-26 23:55 ` kernel test robot
2022-05-27 7:34 ` kernel test robot
2022-05-27 9:17 ` kernel test robot
2022-05-26 21:34 ` [PATCH v4 bpf-next 07/14] bpf: Define acquire-release pairs for kfuncs Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 08/14] selftests/bpf: Add verifier tests for forced kfunc ref args Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 09/14] selftests/bpf: Add C tests for rdonly PTR_TO_BTF_ID Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 10/14] selftests/bpf: Add verifier " Lorenzo Bianconi
2022-05-26 21:34 ` [PATCH v4 bpf-next 11/14] net: netfilter: add kfunc helper to update ct timeout Lorenzo Bianconi
2022-05-26 21:35 ` [PATCH v4 bpf-next 12/14] net: netfilter: add kfunc helpers to alloc and insert a new ct entry Lorenzo Bianconi
2022-05-26 21:35 ` [PATCH v4 bpf-next 13/14] selftests/bpf: add selftest for bpf_xdp_ct_add and bpf_ct_refresh_timeout kfunc Lorenzo Bianconi
2022-05-26 21:35 ` [PATCH v4 bpf-next 14/14] selftests/bpf: Add negative tests for bpf_nf Lorenzo Bianconi
2022-06-11 20:11 ` [PATCH v4 bpf-next 00/14] net: netfilter: add kfunc helper to update ct timeout Alexei Starovoitov
2022-06-13 16:14 ` Kumar Kartikeya Dwivedi
2022-06-13 22:15 ` Alexei Starovoitov
2022-06-14 2:23 ` Kumar Kartikeya Dwivedi
2022-06-17 20:45 ` Alexei Starovoitov
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