netdev - Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

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Date:	Fri, 4 Sep 2015 13:58:25 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Tycho Andersen <tycho.andersen@...onical.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

On Fri, Sep 04, 2015 at 01:50:55PM -0700, Kees Cook wrote:
> On Fri, Sep 4, 2015 at 1:45 PM, Tycho Andersen
> <tycho.andersen@...onical.com> wrote:
> > On Fri, Sep 04, 2015 at 01:17:30PM -0700, Kees Cook wrote:
> >> On Fri, Sep 4, 2015 at 9:04 AM, Tycho Andersen
> >> <tycho.andersen@...onical.com> wrote:
> >> > This commit adds a way to dump eBPF programs. The initial implementation
> >> > doesn't support maps, and therefore only allows dumping seccomp ebpf
> >> > programs which themselves don't currently support maps.
> >> >
> >> > We export the GPL bit as well as a unique ID for the program so that
> >>
> >> This unique ID appears to be the heap address for the prog. That's a
> >> huge leak, and should not be done. We don't want to introduce new
> >> kernel address leaks while we're trying to fix the remaining ones.
> >> Shouldn't the "unique ID" be the fd itself? I imagine KCMP_FILE
> >> could be used, for example.
> >
> > No; we acquire the fd per process, so if a task installs a filter and
> > then forks N times, we'll grab N (+1) copies of the filter from N (+1)
> > different file descriptors. Ideally, we'd have some way to figure out
> > that these were all the same. Some sort of prog_id is one way,
> > although there may be others.
> 
> If KCMP_FILE or a new KCMP_BPF isn't possible, then we'll probably
> have to add a unique id (counter) to all bpf programs as they're
> created.

I think tweaking KCMP_FILE for anon_inodes should do the trick
and should work at the end (if it's not working already).

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