netdev - Re: [PATCH bpf] bpf: fix truncated jump targets on heavy expansions

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Date:   Thu, 17 May 2018 16:09:12 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: fix truncated jump targets on heavy expansions

On Thu, May 17, 2018 at 01:44:11AM +0200, Daniel Borkmann wrote:
> Recently during testing, I ran into the following panic:
> 
> Therefore it becomes necessary to detect and reject any such occasions
> in a generic way for native eBPF and cBPF to eBPF migrations. For
> the latter we can simply check bounds in the bpf_convert_filter()'s
> BPF_EMIT_JMP helper macro and bail out once we surpass limits. The
> bpf_patch_insn_single() for native eBPF (and cBPF to eBPF in case
> of subsequent hardening) is a bit more complex in that we need to
> detect such truncations before hitting the bpf_prog_realloc(). Thus
> the latter is split into an extra pass to probe problematic offsets
> on the original program in order to fail early. With that in place
> and carefully tested I no longer hit the panic and the rewrites are
> rejected properly. The above example panic I've seen on bpf-next,
> though the issue itself is generic in that a guard against this issue
> in bpf seems more appropriate in this case.
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Nice catch! Applied.