Re: v5 of seccomp filter c/r patches

[Daniel Borkmann <daniel@iogearbox.net>]

On 10/03/2015 12:44 AM, Tycho Andersen wrote:
> On Fri, Oct 02, 2015 at 02:10:24PM -0700, Kees Cook wrote:
...
> Ok, how about,
>
> struct sock_filter insns[BPF_MAXINSNS];
> insn_cnt = ptrace(PTRACE_SECCOMP_GET_FILTER, pid, insns, i);

Would also be good that when the storage buffer (insns) is NULL,
it just returns you the number of sock_filter insns (or 0 when
nothing attached).

That would be consistent with classic socket filters (see
sk_get_filter()), and user space could allocate a specific
size instead of always passing in max insns.

> when asking for the ith filter? It returns either the number of
> instructions, -EINVAL if something was wrong (i, pid,
> CONFIG_CHECKPOINT_RESTORE isn't enabled). While it would always
> succeed now, if/when the underlying filter was not created from a bpf
> classic filter, we can return -EMEDIUMTYPE? (Suggestions welcome, I
> picked this mostly based on what sounds nice.)
>
> Tycho
>