From: Edward Cree <ecree@solarflare.com>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Alexei Starovoitov <ast@fb.com>,
"Daniel Borkmann" <daniel@iogearbox.net>,
<netdev@vger.kernel.org>,
iovisor-dev <iovisor-dev@lists.iovisor.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [iovisor-dev] [PATCH v3 net-next 02/12] bpf/verifier: rework value tracking
Date: Mon, 17 Jul 2017 18:02:02 +0100 [thread overview]
Message-ID: <fbd2b381-c444-a736-2d9e-aa83d6153178@solarflare.com> (raw)
In-Reply-To: <12DCE590-7F67-4639-A825-61A24AC44ED3@gmail.com>
On 12/07/17 23:07, Nadav Amit wrote:
> Edward Cree <ecree@solarflare.com> wrote:
>> In this specific case, there was a bug before: if (say) src and dst were
>> both unknown bytes (so range 0 to 255), it would compute the new min and max
>> to be 0, so it would think the result is known to be 0. But that's wrong,
>> because it could be anything from -255 to +255. The bug's implications are
>> that it could be used to construct an out-of-range offset to (say) a map
>> pointer which the verifier would think was in-range and thus accept.
> This sounds like a serious bug that may need to be backported to stable
> versions, no? In this case I would assume it should be in a separate patch
> so it could be applied separately.
Having looked deeper into this in attempting to create a test that the existing
verifier would fail, it turns out that in the existing verifier that BPF_SUB
handling is dead code. If (for instance) we subtract an UNKNOWN_VALUE from a
PTR_TO_MAP_VALUE_ADJ, that code will be run, but afterwards we will
mark_reg_unknown_value() the register (bottom of check_alu_op()) making our
previous min/max determination irrelevant.
So there's nothing to backport, and if I did change this in its own patch,
there'd be no way to test it. (I have, however, added a test covering this
codepath in the new verifier.)
-Ed
next prev parent reply other threads:[~2017-07-17 17:02 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-27 12:53 [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier Edward Cree
2017-06-27 12:56 ` [PATCH v3 net-next 01/12] selftests/bpf: add test for mixed signed and unsigned bounds checks Edward Cree
2017-06-28 13:51 ` Daniel Borkmann
2017-06-27 12:56 ` [PATCH v3 net-next 02/12] bpf/verifier: rework value tracking Edward Cree
2017-06-28 15:15 ` Daniel Borkmann
2017-06-28 16:07 ` Edward Cree
2017-06-28 19:44 ` Daniel Borkmann
2017-06-28 17:09 ` Daniel Borkmann
2017-06-28 18:28 ` Edward Cree
2017-06-29 7:48 ` kbuild test robot
2017-07-06 21:21 ` [iovisor-dev] " Nadav Amit
2017-07-07 13:48 ` Edward Cree
2017-07-07 17:45 ` Nadav Amit
2017-07-08 0:54 ` Nadav Amit
2017-07-12 19:13 ` Edward Cree
2017-07-12 22:07 ` Nadav Amit
2017-07-17 17:02 ` Edward Cree [this message]
2017-06-27 12:57 ` [PATCH v3 net-next 03/12] nfp: change bpf verifier hooks to match new verifier data structures Edward Cree
2017-06-28 20:47 ` Daniel Borkmann
2017-06-29 3:47 ` Jakub Kicinski
2017-06-27 12:57 ` [PATCH v3 net-next 04/12] bpf/verifier: track signed and unsigned min/max values Edward Cree
2017-06-27 12:58 ` [PATCH v3 net-next 05/12] bpf/verifier: more concise register state logs for constant var_off Edward Cree
2017-06-27 12:58 ` [PATCH v3 net-next 06/12] selftests/bpf: change test_verifier expectations Edward Cree
2017-06-27 12:59 ` [PATCH v3 net-next 07/12] selftests/bpf: rewrite test_align Edward Cree
2017-06-27 12:59 ` [PATCH v3 net-next 08/12] selftests/bpf: add a test to test_align Edward Cree
2017-06-27 12:59 ` [PATCH v3 net-next 09/12] selftests/bpf: add test for bogus operations on pointers Edward Cree
2017-06-27 12:59 ` [PATCH v3 net-next 10/12] selftests/bpf: don't try to access past MAX_PACKET_OFF in test_verifier Edward Cree
2017-06-27 13:00 ` [PATCH v3 net-next 11/12] selftests/bpf: add tests for subtraction & negative numbers Edward Cree
2017-06-27 13:00 ` [PATCH v3 net-next 12/12] selftests/bpf: variable offset negative tests Edward Cree
2017-06-28 13:50 ` [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier Daniel Borkmann
2017-06-28 14:11 ` Edward Cree
2017-06-28 20:38 ` Daniel Borkmann
2017-06-28 21:37 ` Alexei Starovoitov
2017-06-30 16:44 ` Edward Cree
2017-06-30 17:34 ` [TEST PATCH] bpf/verifier: roll back ptr&const handling, and fix signed bounds Edward Cree
2017-06-30 18:15 ` [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier Alexei Starovoitov
2017-07-04 19:22 ` Edward Cree
2017-07-04 22:28 ` Daniel Borkmann
2017-07-06 18:27 ` Edward Cree
2017-07-07 9:14 ` Daniel Borkmann
2017-07-07 12:50 ` Edward Cree
2017-07-07 13:05 ` Daniel Borkmann
2017-07-06 14:07 ` Edward Cree
2017-07-14 20:03 ` [iovisor-dev] " Y Song
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