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SubjectRe: [PATCH] sysctl: Add the kernel.ns_last_pid control
On 11/29/2011 09:47 PM, Oleg Nesterov wrote:
> On 11/28, Pavel Emelyanov wrote:
>>
>> --- a/kernel/pid_namespace.c
>> +++ b/kernel/pid_namespace.c
>> @@ -191,9 +191,40 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>> return;
>> }
>>
>> +static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>> + void __user *buffer, size_t *lenp, loff_t *ppos)
>> +{
>> + struct ctl_table tmp = *table;
>> +
>> + if (write && !capable(CAP_SYS_ADMIN))
>> + return -EPERM;
>> +
>> + /*
>> + * Writing directly to ns' last_pid field is OK, since this field
>> + * is volatile in a living namespace anyway and a code writing to
>> + * it should synchronize its usage with external means.
>> + */
>> +
>> + tmp.data = &current->nsproxy->pid_ns->last_pid;
>> + return proc_dointvec(&tmp, write, buffer, lenp, ppos);
>> +}
>> +
>> +static struct ctl_table pid_ns_ctl_table[] = {
>> + {
>> + .procname = "ns_last_pid",
>> + .maxlen = sizeof(int),
>> + .mode = 0666, /* permissions are checked in the handler */
>> + .proc_handler = pid_ns_ctl_handler,
>> + },
>> + { }
>> +};
>> +
>> +static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
>> +
>> static __init int pid_namespaces_init(void)
>> {
>> pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
>> + register_sysctl_paths(kern_path, pid_ns_ctl_table);
>> return 0;
>> }
>
> Hmm. This way it depends on CONFIG_PID_NS.

Yes, since this _is_ for namespaces. As we've found out this is close to completely
unusable in the initial namespace in which tasks are just forking without caring
much about what CAP_SYS_ADMIN-s think about this.

> Can't we simply add an entry into kern_table[] ?

And store the .proc_handler function dealing with somewhat which is pid namespace
specific in the same generic file?

> And without ns_, just /proc/sys/kernel/last_pid.

But that's the namespace's last pid, not just some system-wide last pid.

> Oleg.
>
> .
>



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