netdev - Re: [PATCH bpf] bpf: reject stores into ctx via st and xadd

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Message-ID: <20180116231300.a6y4tniulkq6xb4x@ast-mbp>
Date:   Tue, 16 Jan 2018 15:13:02 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: reject stores into ctx via st and xadd

On Tue, Jan 16, 2018 at 11:30:10PM +0100, Daniel Borkmann wrote:
> Alexei found that verifier does not reject stores into context
> via BPF_ST instead of BPF_STX. And while looking at it, we
> also should not allow XADD variant of BPF_STX.
> 
> The context rewriter is only assuming either BPF_LDX_MEM- or
> BPF_STX_MEM-type operations, thus reject anything other than
> that so that assumptions in the rewriter properly hold. Add
> test cases as well for BPF selftests.
> 
> Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
> Reported-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied, thank you Daniel.

all bugs are eventually shallow.
For this one we even had two broken testcases. Ouch.