linux-kernel - Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

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Date:	Thu, 12 Jan 2012 15:50:40 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, eparis@...hat.com,
	djm@...drot.org, torvalds@...ux-foundation.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, luto@....edu, mingo@...e.hu,
	akpm@...ux-foundation.org, khilman@...com, borislav.petkov@....com,
	amwang@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com
Subject: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using
	BPF

On 01/11, Will Drewry wrote:
>
> This patch adds support for seccomp mode 2.  This mode enables dynamic
> enforcement of system call filtering policy in the kernel as specified
> by a userland task.  The policy is expressed in terms of a BPF program,
> as is used for userland-exposed socket filtering.  Instead of network
> data, the BPF program is evaluated over struct user_regs_struct at the
> time of the system call (as retrieved using regviews).

Cool ;)

I didn't really read this patch yet, just one nit.

> +#define seccomp_filter_init_task(_tsk) do { \
> +	(_tsk)->seccomp.filter = NULL; \
> +} while (0);

Cosmetic and subjective, but imho it would be better to add inline
functions instead of define's.

> @@ -166,6 +167,7 @@ void free_task(struct task_struct *tsk)
>  	free_thread_info(tsk->stack);
>  	rt_mutex_debug_task_free(tsk);
>  	ftrace_graph_exit_task(tsk);
> +	seccomp_filter_free_task(tsk);
>  	free_task_struct(tsk);
>  }
>  EXPORT_SYMBOL(free_task);
> @@ -1209,6 +1211,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	/* Perform scheduler related setup. Assign this task to a CPU. */
>  	sched_fork(p);
>  
> +	seccomp_filter_init_task(p);

This doesn't look right or I missed something. something seccomp_filter_init_task()
should be called right after dup_task_struct(), at least before copy process can
fail.

Otherwise copy_process()->free_fork()->seccomp_filter_free_task() can put
current->seccomp.filter copied by arch_dup_task_struct().

> +struct seccomp_filter {
> +	struct kref usage;
> +	struct pid *creator;

Why? seccomp_filter->creator is never used, no?

Oleg.

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