netdev - Re: [PATCH net][v2] bpf: fix range arithmetic for bpf map access

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Message-ID: <20161115031016.GA10323@ast-mbp.thefacebook.com>
Date:   Mon, 14 Nov 2016 19:10:17 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Josef Bacik <jbacik@...com>
Cc:     jannh@...gle.com, ast@...nel.org, daniel@...earbox.net,
        davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net][v2] bpf: fix range arithmetic for bpf map access

On Mon, Nov 14, 2016 at 03:45:36PM -0500, Josef Bacik wrote:
> I made some invalid assumptions with BPF_AND and BPF_MOD that could result in
> invalid accesses to bpf map entries.  Fix this up by doing a few things
> 
> 1) Kill BPF_MOD support.  This doesn't actually get used by the compiler in real
> life and just adds extra complexity.
> 
> 2) Fix the logic for BPF_AND, don't allow AND of negative numbers and set the
> minimum value to 0 for positive AND's.
> 
> 3) Don't do operations on the ranges if they are set to the limits, as they are
> by definition undefined, and allowing arithmetic operations on those values
> could make them appear valid when they really aren't.
> 
> This fixes the testcase provided by Jann as well as a few other theoretical
> problems.
> 
> Reported-by: Jann Horn <jannh@...gle.com>
> Signed-off-by: Josef Bacik <jbacik@...com>

lgtm.
Acked-by: Alexei Starovoitov <ast@...nel.org>

Jann, could you please double check the logic.
Thanks!