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SubjectRe: [PATCH 7/9] syslog_ns: implement function for creating syslog ns
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@huawei.com>
> ---
> 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;
>



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