linux-kernel - Re: [PATCH 2/4] seccomp: rework seccomp_prepare

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Message-ID: <55423858.9040108@freebox.fr>
Date:	Thu, 30 Apr 2015 16:12:40 +0200
From:	Nicolas Schichan <nschichan@...ebox.fr>
To:	Daniel Borkmann <daniel@...earbox.net>,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	ast@...mgrid.com, davem@...emloft.net
Subject: Re: [PATCH 2/4] seccomp: rework seccomp_prepare_filter().

On 04/30/2015 02:46 PM, Daniel Borkmann wrote:
>> 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) {
>         __bpf_prog_release(fp);
>         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,
>                     fp->len);
>         if (err) {
>             __bpf_prog_release(fp);
>             return ERR_PTR(err);
>         }
>     }
> 
>     /* Probe if we can JIT compile the filter and if so, do
>      * the compilation of the filter.
>      */
>     bpf_jit_compile(fp);
> 
>     /* 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);

Thanks for the precisions, I'll look into that.

-- 
Nicolas Schichan
Freebox SAS
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