From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next] bpf: cgroup skb progs cannot access ld_abs/ind
Date: Tue, 06 Jun 2017 16:40:05 -0400 (EDT)
Message-ID: <20170606.164005.76474638904598005.davem@davemloft.net>
References: <1851c3df45588eb96803995a3ceff32819612386.1496766858.git.daniel@iogearbox.net>
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Cc: netdev@vger.kernel.org, fengc@google.com, ast@kernel.org
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From: Daniel Borkmann <daniel@iogearbox.net>
Date: Tue,  6 Jun 2017 18:38:04 +0200

> Commit fb9a307d11d6 ("bpf: Allow CGROUP_SKB eBPF program to
> access sk_buff") enabled programs of BPF_PROG_TYPE_CGROUP_SKB
> type to use ld_abs/ind instructions. However, at this point,
> we cannot use them, since offsets relative to SKF_LL_OFF will
> end up pointing skb_mac_header(skb) out of bounds since in the
> egress path it is not yet set at that point in time, but only
> after __dev_queue_xmit() did a general reset on the mac header.
> bpf_internal_load_pointer_neg_helper() will then end up reading
> data from a wrong offset.
> 
> BPF_PROG_TYPE_CGROUP_SKB programs can use bpf_skb_load_bytes()
> already to access packet data, which is also more flexible than
> the insns carried over from cBPF.
> 
> Fixes: fb9a307d11d6 ("bpf: Allow CGROUP_SKB eBPF program to access sk_buff")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Aha, I see, applied.

Thanks!