From: Andy Lutomirski <luto@amacapital.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
Andy Lutomirski <luto@kernel.org>,
Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Eric Dumazet <edumazet@google.com>,
Eric Biggers <ebiggers3@gmail.com>,
Tom Herbert <tom@herbertland.com>,
"David S. Miller" <davem@davemloft.net>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [RFC PATCH 4.10 3/6] bpf: Use SHA256 instead of SHA1 for bpf digests
Date: Mon, 26 Dec 2016 18:08:18 -0800 [thread overview]
Message-ID: <CALCETrWsR6Lsy_gY1uBMh2UbYm+Z7v5mV_96bSeb6Ru8hyhA2A@mail.gmail.com> (raw)
In-Reply-To: <20161227013644.GA96815@ast-mbp.thefacebook.com>
On Mon, Dec 26, 2016 at 5:36 PM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Sat, Dec 24, 2016 at 08:59:53PM +0100, Daniel Borkmann wrote:
>> On 12/24/2016 03:22 AM, Andy Lutomirski wrote:
>> >BPF digests are intended to be used to avoid reloading programs that
>> >are already loaded. For use cases (CRIU?) where untrusted programs
>> >are involved, intentional hash collisions could cause the wrong BPF
>> >program to execute. Additionally, if BPF digests are ever used
>> >in-kernel to skip verification, a hash collision could give privilege
>> >escalation directly.
>>
>> Just for the record, digests will never ever be used to skip the
>> verification step, so I don't know why this idea even comes up
>> here (?) or is part of the changelog? As this will never be done
>> anyway, rather drop that part so we can avoid confusion on this?
>
> +1 to what Daniel said above.
>
> For the others let me explain what this patch set is actually
> trying to accomplish.
The patch:
a) cleans up the code and
b) uses a cryptographic hash that is actually believed to satisfy the
definition of a cryptographic hash.
There's no excuse for not doing b.
> and I have an obvious NACK for bpf related patches 3,4,5,6.
Did you *read* the ones that were pure cleanups?
>
> sha1 is 20 bytes which is already a bit long to print and copy paste by humans.
> whereas 4 byte jhash is a bit too short, since collisions are not that rare
> and may lead to incorrect assumptions from the users that develop the programs.
> I would prefer something in 6-10 byte range that prevents collisions most of
> the time and short to print as hex, but I don't know of anything like this
> in the existing kernel and inventing bpf specific hash is not great.
> Another requirement for debugging (and prog_digest) that user space
> should be able to produce the same hash without asking kernel, so
> sha1 fits that as well, since it's well known and easy to put into library.
Then truncate them in user space.
next prev parent reply other threads:[~2016-12-27 2:08 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-24 2:22 [RFC PATCH 4.10 0/6] Switch BPF's digest to SHA256 Andy Lutomirski
2016-12-24 2:22 ` [RFC PATCH 4.10 1/6] crypto/sha256: Refactor the API so it can be used without shash Andy Lutomirski
2016-12-24 2:26 ` Andy Lutomirski
2016-12-24 10:33 ` Ard Biesheuvel
2016-12-24 17:57 ` Andy Lutomirski
2016-12-26 7:57 ` Herbert Xu
2016-12-26 17:51 ` Ard Biesheuvel
2016-12-26 18:08 ` Andy Lutomirski
2016-12-27 9:58 ` Herbert Xu
2016-12-27 14:16 ` Daniel Borkmann
2016-12-27 19:00 ` Andy Lutomirski
2016-12-24 2:22 ` [RFC PATCH 4.10 2/6] crypto/sha256: Make the sha256 library functions selectable Andy Lutomirski
2016-12-24 2:22 ` [RFC PATCH 4.10 3/6] bpf: Use SHA256 instead of SHA1 for bpf digests Andy Lutomirski
2016-12-24 19:59 ` Daniel Borkmann
2016-12-27 1:36 ` Alexei Starovoitov
2016-12-27 2:08 ` Andy Lutomirski [this message]
2016-12-24 2:22 ` [RFC PATCH 4.10 4/6] bpf: Avoid copying the entire BPF program when hashing it Andy Lutomirski
2016-12-24 2:22 ` [RFC PATCH 4.10 5/6] bpf: Rename fdinfo's prog_digest to prog_sha256 Andy Lutomirski
2016-12-24 2:22 ` [RFC PATCH 4.10 6/6] net: Rename TCA*BPF_DIGEST to ..._SHA256 Andy Lutomirski
2016-12-26 8:20 ` [RFC PATCH 4.10 0/6] Switch BPF's digest to SHA256 Herbert Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CALCETrWsR6Lsy_gY1uBMh2UbYm+Z7v5mV_96bSeb6Ru8hyhA2A@mail.gmail.com \
--to=luto@amacapital.net \
--cc=Jason@zx2c4.com \
--cc=alexei.starovoitov@gmail.com \
--cc=ast@kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=ebiggers3@gmail.com \
--cc=edumazet@google.com \
--cc=hannes@stressinduktion.org \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=tom@herbertland.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).