netdev - Re: [PATCH net] bpf: expose netns inode to bpf programs

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Date:   Thu, 26 Jan 2017 09:46:32 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Ahern <dsa@...ulusnetworks.com>,
        Tejun Heo <tj@...nel.org>, Thomas Graf <tgraf@...g.ch>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net] bpf: expose netns inode to bpf programs

On 1/26/17 8:37 AM, Andy Lutomirski wrote:
>> Think of bpf programs as safe kernel modules. They don't have
>> confined boundaries and program authors, if not careful, can shoot
>> themselves in the foot. We're not trying to prevent that because
>> it's impossible to check that the program is sane. Just like
>> it's impossible to check that kernel module is sane.
>> But in case of bpf we check that bpf program is _safe_ from the kernel
>> point of view. If it's doing some garbage, it's program's business.
>> Does it make more sense now?
>>
>
> With all due respect, I think this is not an acceptable way to think
> about BPF at all.  If you think of BPF this way, I think there needs
> to be a real discussion at KS or similar as to whether this is okay.
> The reason is simple: the kernel promises a stable ABI to userspace
> but not to kernel modules.  By thinking of BPF as more like a module,
> you're taking a big shortcut that will either result in ABI breakage
> down the road or in committing to a problematic stable ABI.

you misunderstood the analogy.
bpf abi is certainly stable. that's why we were careful of not
exposing anything to it that is not already stable.