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 [off-list ref] wrote:

On Fri, Aug 15, 2014 at 12:20 PM, Andy Lutomirski [off-list ref] wrote:

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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.

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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.

--Andy