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Date:	Fri, 15 Aug 2014 12:32:41 -0700
From:	Andy Lutomirski <>
To:	Alexei Starovoitov <>
Cc:	"David S. Miller" <>,
	Ingo Molnar <>,
	Linus Torvalds <>,
	Steven Rostedt <>,
	Daniel Borkmann <>,
	Chema Gonzalez <>,
	Eric Dumazet <>,
	Peter Zijlstra <>,
	"H. Peter Anvin" <>,
	Andrew Morton <>,
	Kees Cook <>,
	Linux API <>,
	Network Development <>,
	"" <>
Subject: Re: [PATCH RFC v4 net-next 17/26] tracing: allow eBPF programs to be
 attached to events

On Fri, Aug 15, 2014 at 12:29 PM, Alexei Starovoitov <> wrote:
> On Fri, Aug 15, 2014 at 12:20 PM, Andy Lutomirski <> wrote:
>>>> I don't think that fixing this should be a prerequisite for merging,
>>>> since the risk is so small.  Nonetheless, it would be nice.  (This
>>>> family of attacks has lead to several root vulnerabilities in the
>>>> past.)
>>> Ok. I think keeping a track of pid between open and write is kinda
>>> ugly.
>> Agreed.
>> TBH, I would just add a comment to the open implementation saying
>> that, if unprivileged or less privileged open is allowed, then this
>> needs to be fixed.
> ok. will do.
>>> Should we add some new CAP flag and check it for all file
>>> ops? Another option is to conditionally make open() of tracing
>>> files as cloexec...
>> That won't help.  The same attack can be done with SCM_RIGHTS, and
>> cloexec can be cleared.
> ouch, can we then make ebpf FDs and may be debugfs FDs
> not passable at all? Otherwise it feels that generality and
> flexibility of FDs is becoming a burden.

I'm not sure there's much of a general problem.  The issue is when
there's an fd for which write(2) (or other
assumed-to-not-check-permissions calls like read, pread, pwrite, etc)
depend on context.  This is historically an issue for netlink and
various /proc files.

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