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

[YiFei Zhu]

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

YiFei Zhu