Re: [PATCH net] bpf: rework prog_digest into prog_tag

[David Miller <davem@davemloft.net>]

From: Daniel Borkmann <daniel@iogearbox.net>
Date: Fri, 13 Jan 2017 23:38:15 +0100

> Commit 7bd509e311f4 ("bpf: add prog_digest and expose it via
> fdinfo/netlink") was recently discussed, partially due to
> admittedly suboptimal name of "prog_digest" in combination
> with sha1 hash usage, thus inevitably and rightfully concerns
> about its security in terms of collision resistance were
> raised with regards to use-cases.
> 
> The intended use cases are for debugging resp. introspection
> only for providing a stable "tag" over the instruction sequence
> that both kernel and user space can calculate independently.
> It's not usable at all for making a security relevant decision.
> So collisions where two different instruction sequences generate
> the same tag can happen, but ideally at a rather low rate. The
> "tag" will be dumped in hex and is short enough to introspect
> in tracepoints or kallsyms output along with other data such
> as stack trace, etc. Thus, this patch performs a rename into
> prog_tag and truncates the tag to a short output (64 bits) to
> make it obvious it's not collision-free.
> 
> Should in future a hash or facility be needed with a security
> relevant focus, then we can think about requirements, constraints,
> etc that would fit to that situation. For now, rework the exposed
> parts for the current use cases as long as nothing has been
> released yet. Tested on x86_64 and s390x.
> 
> Fixes: 7bd509e311f4 ("bpf: add prog_digest and expose it via fdinfo/netlink")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Applied, thanks.