linux-kernel - Re: [PATCH v17 08/15] seccomp: add system call filtering using BPF

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Date:	Sat, 31 Mar 2012 08:40:33 +0400
From:	Vladimir Murzin <murzin.v@...il.com>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-arch@...r.kernel.org,
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Subject: Re: [PATCH v17 08/15] seccomp: add system call filtering using BPF

Hi Will,

On Thu, Mar 29, 2012 at 03:01:53PM -0500, Will Drewry wrote:

snipped

> +
> +/* Limit any path through the tree to 256KB worth of instructions. */
> +#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
> +
> +static void seccomp_filter_log_failure(int syscall)
> +{
> +	int compat = 0;
> +#ifdef CONFIG_COMPAT
> +	compat = is_compat_task();
> +#endif
> +	pr_info("%s[%d]: %ssystem call %d blocked at 0x%lx\n",
> +		current->comm, task_pid_nr(current),
> +		(compat ? "compat " : ""),
> +		syscall, KSTK_EIP(current));
> +}

snipped

> +/**
> + * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
> + * @user_filter: pointer to the user data containing a sock_fprog.
> + *
> + * Returns 0 on success and non-zero otherwise.
> + */
> +long seccomp_attach_user_filter(char __user *user_filter)
> +{
> +	struct sock_fprog fprog;
> +	long ret = -EFAULT;
> +
> +#ifdef CONFIG_COMPAT
> +	if (is_compat_task()) {
> +		struct compat_sock_fprog fprog32;
> +		if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
> +			goto out;
> +		fprog.len = fprog32.len;
> +		fprog.filter = compat_ptr(fprog32.filter);
> +	} else /* falls through to the if below. */
> +#endif
> +	if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
> +		goto out;
> +	ret = seccomp_attach_filter(&fprog);
> +out:
> +	return ret;
> +}

Do we really need to surround is_compat_task() with CNFIG_COMPAT?
It seems that this case has already handled in compat.h [1]

[1] http://lxr.linux.no/#linux+v3.3/include/linux/compat.h#L566

Best wishes
Vladimir Murzin

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