Re: [PATCH 2/4] seccomp: rework seccomp_prepare_filter().

From: Daniel Borkmann
Date: Thu Apr 30 2015 - 08:46:47 EST

On 04/30/2015 02:27 PM, Nicolas Schichan wrote:
I'll take more care about the receiver list for the v2 of this serie.

Ok, cool.

I see, you need that to make it available to the old bpf_jit_compile()
for probing on classic JITs. Actually, I really would prefer, if instead
of duplicating that code, you could export bpf_prepare_filter() and
pass seccomp_check_filter() as an argument to bpf_prepare_filter().

Just to be sure you want me to pass a pointer to seccomp_check_filter to
bpf_prepare_filter so that it can run it between bpf_check_classic() and
bpf_jit_compile ?

For example, what comes to mind is something along these lines:

struct bpf_prog *
bpf_prepare_filter(struct bpf_prog *fp,
int (*aux_trans_classic)(struct sock_filter *filter,
unsigned int flen))
int err;

fp->bpf_func = NULL;
fp->jited = false;

err = bpf_check_classic(fp->insns, fp->len);
if (err) {
return ERR_PTR(err);

/* There might be additional checks and transformations
* needed on classic filters, f.e. in case of seccomp.
if (aux_trans_classic) {
err = aux_trans_classic(fp->insns,
if (err) {
return ERR_PTR(err);

/* Probe if we can JIT compile the filter and if so, do
* the compilation of the filter.

/* JIT compiler couldn't process this filter, so do the
* internal BPF translation for the optimized interpreter.
if (!fp->jited)
fp = bpf_migrate_filter(fp);

return fp;

From seccomp side, you invoke:

... bpf_prepare_filter(fp, seccomp_check_filter);

I would actually like to see that customized code in seccomp_prepare_filter()
further reduced instead of increased, would certainly make it easier to
maintain and understand.

Do you think something like the above is possible?

Otherwise, in case bpf_prepare_filter() changes, people will easily
forget to update seccomp related code, really.

Fair point.


Thanks a lot,
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