From: Daniel Borkmann <daniel@iogearbox•net>
To: Ingo Molnar <mingo@kernel•org>, Alexei Starovoitov <ast@plumgrid•com>
Cc: "David S. Miller" <davem@davemloft•net>,
Andy Lutomirski <luto@amacapital•net>,
Hannes Frederic Sowa <hannes@stressinduktion•org>,
Eric Dumazet <edumazet@google•com>,
Kees Cook <keescook@chromium•org>,
linux-api@vger•kernel.org, netdev@vger•kernel.org,
linux-kernel@vger•kernel.org
Subject: Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs
Date: Tue, 06 Oct 2015 10:05:15 +0200 [thread overview]
Message-ID: <561380BB.4040506@iogearbox.net> (raw)
In-Reply-To: <20151006071347.GB14093@gmail.com>
On 10/06/2015 09:13 AM, Ingo Molnar wrote:
>
> * Alexei Starovoitov <ast@plumgrid•com> wrote:
>
>> On 10/5/15 3:14 PM, Daniel Borkmann wrote:
>>> One scenario that comes to mind ... what happens when there are kernel
>>> pointers stored in skb->cb[] (either from the current layer or an old
>>> one from a different layer that the skb went through previously, but
>>> which did not get overwritten)?
>>>
>>> Socket filters could read a portion of skb->cb[] also when unprived and
>>> leak that out through maps. I think the verifier doesn't catch that,
>>> right?
>>
>> grrr. indeed. previous layer before sk_filter() can leave junk in there.
>
> Could this be solved by activating zeroing/sanitizing of this data if there's an
> active BPF function around that can access that socket?
I think this check could only be done in sk_filter() for testing these
conditions (unprivileged user + access to cb area), so it would need to
happen from outside a native eBPF program. :/ Also classic BPF would
then need to test for it, since a socket filter doesn't really know
whether native eBPF is loaded there or a classic-to-eBPF transformed one,
and classic never makes use of this. Anyway, it could be done by adding
a bit flag cb_access:1 to the bpf_prog, set it during eBPF verification
phase, and test it inside sk_filter() if I see it correctly.
The reason is that this sanitizing must only be done in the 'top-level'
program that is run from sk_filter() _directly_, because a user at any
time could decide to put an already loaded eBPF fd into a tail call map.
And cb[] is then used to pass args/state around between two programs,
thus it cannot be unconditionally cleared from within the program. The
association to a socket filter (SO_ATTACH_BPF) happens at a later time
after a native eBPF program has already been loaded via bpf(2).
Thanks,
Daniel
next prev parent reply other threads:[~2015-10-06 8:05 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-05 20:48 [PATCH net-next 0/2] bpf: unprivileged Alexei Starovoitov
2015-10-05 20:48 ` [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov
2015-10-05 22:14 ` Daniel Borkmann
[not found] ` <5612F639.2050305-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>
2015-10-06 0:51 ` Alexei Starovoitov
[not found] ` <56131B1F.80002-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-06 7:13 ` Ingo Molnar
2015-10-06 8:05 ` Daniel Borkmann [this message]
2015-10-06 8:20 ` Ingo Molnar
[not found] ` <20151006082048.GA18287-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-10-06 8:39 ` Daniel Borkmann
[not found] ` <561388D1.30406-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>
2015-10-06 17:50 ` Alexei Starovoitov
2015-10-06 17:56 ` Eric Dumazet
[not found] ` <1444154160.9555.5.camel-XN9IlZ5yJG9HTL0Zs8A6p/gx64E7kk8eUsxypvmhUTTZJqsBc5GL+g@public.gmane.org>
2015-10-06 18:05 ` Andy Lutomirski
2015-10-07 6:05 ` Ingo Molnar
2015-10-06 19:26 ` Alexei Starovoitov
[not found] ` <561409EC.5050005-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-06 18:03 ` Daniel Borkmann
2015-10-06 12:45 ` Daniel Borkmann
2015-10-07 21:20 ` Alexei Starovoitov
[not found] ` <56158CAF.9030209-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-07 22:07 ` Daniel Borkmann
2015-10-07 22:22 ` Kees Cook
2015-10-07 23:49 ` Alexei Starovoitov
[not found] ` <5615AF92.50402-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-08 6:21 ` Ingo Molnar
2015-10-08 6:30 ` Alexei Starovoitov
2015-10-08 17:42 ` Kees Cook
[not found] ` <1444078101-29060-2-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-05 21:00 ` Kees Cook
2015-10-05 21:12 ` Alexei Starovoitov
[not found] ` <5612E7C4.1010306-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-10-05 21:16 ` Andy Lutomirski
2015-10-05 21:32 ` Alexei Starovoitov
2015-10-05 22:02 ` Kees Cook
2015-10-06 0:28 ` Alexei Starovoitov
2015-10-08 2:29 ` Alexei Starovoitov
2015-10-05 20:48 ` [PATCH net-next 2/2] bpf: charge user for creation of BPF maps and programs Alexei Starovoitov
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=561380BB.4040506@iogearbox.net \
--to=daniel@iogearbox$(echo .)net \
--cc=ast@plumgrid$(echo .)com \
--cc=davem@davemloft$(echo .)net \
--cc=edumazet@google$(echo .)com \
--cc=hannes@stressinduktion$(echo .)org \
--cc=keescook@chromium$(echo .)org \
--cc=linux-api@vger$(echo .)kernel.org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=luto@amacapital$(echo .)net \
--cc=mingo@kernel$(echo .)org \
--cc=netdev@vger$(echo .)kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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