Re: [iovisor-dev] [PATCH v3 net-next 02/12] bpf/verifier: rework value tracking

From: Nadav Amit
Date: Thu Jul 06 2017 - 17:22:03 EST

Edward Cree via iovisor-dev <iovisor-dev@xxxxxxxxxxxxxxxxx> wrote:

> Tracks value alignment by means of tracking known & unknown bits.
> Tightens some min/max value checks and fixes a couple of bugs therein.
> If pointer leaks are allowed, and adjust_ptr_min_max_vals returns -EACCES,
> treat the pointer as an unknown scalar and try again, because we might be
> able to conclude something about the result (e.g. pointer & 0x40 is either
> 0 or 0x40).
> Signed-off-by: Edward Cree <ecree@xxxxxxxxxxxxxx>
> ---
> include/linux/bpf.h | 34 +-
> include/linux/bpf_verifier.h | 40 +-
> include/linux/tnum.h | 79 ++
> kernel/bpf/Makefile | 2 +-
> kernel/bpf/tnum.c | 163 ++++
> kernel/bpf/verifier.c | 1692 ++++++++++++++++++++++++------------------
> 6 files changed, 1235 insertions(+), 775 deletions(-)


I find it a bit surprising that such huge changes that can affect security
and robustness are performed in one patch. Personally, I cannot comprehend
all of these changes. In addition, I think that it is valuable to describe
in detail the bugs that the patch solves and when they were introduced.

I can bring up some concerns regarding inconsistencies in offset checks and
size, not spilling SCALAR and my wish not to limit packet size. However,
when the patch is that big, I think it is useless.