Re: [PATCH 7/9] syslog_ns: implement function for creating syslog ns

[Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>]

On 07/29/2013 10:31 AM, Rui Xiang wrote:
> Add create_syslog_ns function to create a new ns. We
> must create a user_ns before create a new syslog ns.
> And then tie the new syslog_ns to current user_ns
> instead of original syslog_ns which comes from
> parent user_ns.
> 
> Add a new syslog flag SYSLOG_ACTION_NEW_NS to implement
> a new command(11) of __NR_syslog system call. Through
> that command, we can create a new syslog ns in user
> space.
> 
> Signed-off-by: Rui Xiang <rui.xiang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> ---
>  include/linux/syslog.h |  2 ++
>  kernel/printk.c        | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/include/linux/syslog.h b/include/linux/syslog.h
> index fbf0cb6..df57c21 100644
> --- a/include/linux/syslog.h
> +++ b/include/linux/syslog.h
> @@ -46,6 +46,8 @@
>  #define SYSLOG_ACTION_SIZE_UNREAD    9
>  /* Return size of the log buffer */
>  #define SYSLOG_ACTION_SIZE_BUFFER   10
> +/* Create a new syslog ns */
> +#define SYSLOG_ACTION_NEW_NS        11
>  
>  #define SYSLOG_FROM_READER           0
>  #define SYSLOG_FROM_PROC             1
> diff --git a/kernel/printk.c b/kernel/printk.c
> index fd2d600..6b561db 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -384,6 +384,10 @@ static int check_syslog_permissions(int type, bool from_file,
>  		|| type == SYSLOG_ACTION_CONSOLE_LEVEL)
>  		ns = &init_syslog_ns;
>  
> +	/* create a new syslog ns */
> +	if (type == SYSLOG_ACTION_NEW_NS)
> +		return 0;
> +
>  	if (syslog_action_restricted(type, ns)) {
>  		if (ns_capable(ns->owner, CAP_SYSLOG))
>  			return 0;
> @@ -1131,6 +1135,51 @@ static int syslog_print_all(char __user *buf, int size, bool clear,
>  	return len;
>  }
>  
> +static int create_syslog_ns(void)
> +{
> +	struct user_namespace *userns = current_user_ns();
> +	struct syslog_namespace *oldns, *newns;
> +	int err;
> +
> +	/*
> +	 * syslog ns belongs to a user ns.  So you can only unshare your
> +	 * user_ns if you share a user_ns with your parent userns
> +	 */
> +	if (userns == &init_user_ns ||
> +		userns->syslog_ns != userns->parent->syslog_ns)
> +		return -EINVAL;
> +
> +	if (!ns_capable(userns, CAP_SYSLOG))
> +		return -EPERM;
> +
> +	err = -ENOMEM;
> +	oldns = userns->syslog_ns;
> +	newns = kzalloc(sizeof(*newns), GFP_ATOMIC);
> +	if (!newns)
> +		goto out;
> +	newns->log_buf_len = __LOG_BUF_LEN;
> +	newns->log_buf = kzalloc(newns->log_buf_len, GFP_ATOMIC);
> +	if (!newns->log_buf)
> +		goto out;
> +
> +	newns->owner = get_user_ns(userns);
> +	raw_spin_lock_init(&(newns->logbuf_lock));
> +	newns->logbuf_cpu = UINT_MAX;
> +	newns->dmesg_restrict = oldns->dmesg_restrict;
> +	put_syslog_ns(oldns);
> +	kref_init(&newns->kref);
> +	userns->syslog_ns = newns;

seems like user namespace references the syslog_ns and syslog_ns references
user namespace too? how do you deal with the release?

> +	newns = NULL;
> +
> +	err = 0;
> +out:
> +	if (newns) {
> +		kfree(newns->log_buf);
> +		kfree(newns);
> +	}
> +	return err;
> +}
> +
>  int do_syslog(int type, char __user *buf, int len, bool from_file,
>  		struct syslog_namespace *ns)
>  {
> @@ -1254,6 +1303,9 @@ int do_syslog(int type, char __user *buf, int len, bool from_file,
>  	case SYSLOG_ACTION_SIZE_BUFFER:
>  		error = ns->log_buf_len;
>  		break;
> +	case SYSLOG_ACTION_NEW_NS:
> +		error = create_syslog_ns();
> +		break;
>  	default:
>  		error = -EINVAL;
>  		break;
>