[RFC PATCH bpf-next seccomp 10/12] seccomp-ebpf: Add ability to read user memory

Andy Lutomirski luto at amacapital.net
Thu May 13 14:53:15 UTC 2021

> On May 12, 2021, at 10:26 PM, YiFei Zhu <zhuyifei1999 at gmail.com> wrote:
> On Wed, May 12, 2021 at 5:36 PM Alexei Starovoitov
> <alexei.starovoitov at gmail.com> wrote:
>> Typically the verifier does all the checks at load time to avoid
>> run-time overhead during program execution. Then at attach time we
>> check that attach parameters provided at load time match exactly
>> to those at attach time. ifindex, attach_btf_id, etc fall into this category.
>> Doing something similar it should be possible to avoid
>> doing get_dumpable() at run-time.
> Do you mean to move the check of dumpable to load time instead of
> runtime? I do not think that makes sense. A process may arbitrarily
> set its dumpable attribute during execution via prctl. A process could
> do set itself to non-dumpable, before interacting with sensitive
> information that would better not be possible to be dumped (eg.
> ssh-agent does this [1]). Therefore, being dumpable at one point in
> time does not indicate anything about whether it stays dumpable at a
> later point in time. Besides, seccomp filters are inherited across
> clone and exec, attaching to many tasks with no option to detach. What
> should the load-time check of task dump-ability be against? The
> current task may only be the tip of an iceburg.
> [1] https://github.com/openssh/openssh-portable/blob/2dc328023f60212cd29504fc05d849133ae47355/ssh-agent.c#L1398

First things first: why are you checking dumpable at all?  Once you figure out why and whether it’s needed, you may learn something about what task to check.

I don’t think checking dumpable makes any sense.

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