Re: [PATCH 2/3] lib/kobject_uevent.c: add uevent forwarding function

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 08, 2015 at 10:10:29PM -0400, Michael J. Coss wrote:
> Adds capability to allow userspace programs to forward a given event to
> a specific network namespace as determined by the provided pid.  In
> addition, support for a per-namespace kobject_sequence counter was
> added.  Sysfs was modified to return the correct event counter based on
> the current network namespace.
> 
> Signed-off-by: Michael J. Coss <michael.coss@alcatel-lucent.com>
> ---
>  include/linux/kobject.h     |  3 ++
>  include/net/net_namespace.h |  3 ++
>  kernel/ksysfs.c             | 12 ++++++
>  lib/kobject_uevent.c        | 90 +++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 108 insertions(+)
> 
> diff --git a/include/linux/kobject.h b/include/linux/kobject.h
> index 637f670..d1bb509 100644
> --- a/include/linux/kobject.h
> +++ b/include/linux/kobject.h
> @@ -215,6 +215,9 @@ extern struct kobject *firmware_kobj;
>  int kobject_uevent(struct kobject *kobj, enum kobject_action action);
>  int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
>  			char *envp[]);
> +#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
> +int kobject_uevent_forward(char *buf, size_t len, pid_t pid);
> +#endif
>  
>  __printf(2, 3)
>  int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...);
> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> index e951453..a4013e5 100644
> --- a/include/net/net_namespace.h
> +++ b/include/net/net_namespace.h
> @@ -134,6 +134,9 @@ struct net {
>  #if IS_ENABLED(CONFIG_MPLS)
>  	struct netns_mpls	mpls;
>  #endif
> +#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
> +	u64				kevent_seqnum;
> +#endif
>  	struct sock		*diag_nlsk;
>  	atomic_t		fnhe_genid;
>  };
> diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
> index 6683cce..4bc15fd 100644
> --- a/kernel/ksysfs.c
> +++ b/kernel/ksysfs.c
> @@ -21,6 +21,9 @@
>  #include <linux/compiler.h>
>  
>  #include <linux/rcupdate.h>	/* rcu_expedited */
> +#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
> +#include <net/net_namespace.h>
> +#endif

#if isn't needed here, right?

>  
>  #define KERNEL_ATTR_RO(_name) \
>  static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> @@ -33,6 +36,15 @@ static struct kobj_attribute _name##_attr = \
>  static ssize_t uevent_seqnum_show(struct kobject *kobj,
>  				  struct kobj_attribute *attr, char *buf)
>  {
> +#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
> +	pid_t p = task_pid_vnr(current);
> +	struct net *n = get_net_ns_by_pid(p);
> +
> +	if (n != ERR_PTR(-ESRCH)) {
> +		if (!net_eq(n, &init_net))
> +			return sprintf(buf, "%llu\n", n->kevent_seqnum);
> +	}
> +#endif
>  	return sprintf(buf, "%llu\n", (unsigned long long)uevent_seqnum);
>  }
>  KERNEL_ATTR_RO(uevent_seqnum);
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index d791e33..7589745 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -379,6 +379,96 @@ int kobject_uevent(struct kobject *kobj, enum kobject_action action)
>  }
>  EXPORT_SYMBOL_GPL(kobject_uevent);
>  
> +#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
> +/**
> + * kobject_uevent_forward - forward event to specified network namespace
> + *
> + * @buf: event buffer
> + * @len: event length
> + * @pid: pid of network namespace
> + *
> + * Returns 0 if kobject_uevent_forward() is completed with success or the
> + * corresponding error when it fails.
> + */
> +int kobject_uevent_forward(char *buf, size_t len, pid_t pid)
> +{
> +	int retval = 0;
> +#if defined(CONFIG_NET)
> +	struct uevent_sock *ue_sk;
> +	struct net *pns;
> +	char *p;
> +	u64 num;
> +
> +	/* grab the network namespace of the provided pid */
> +	pns = get_net_ns_by_pid(pid);
> +	if (pns == ERR_PTR(-ESRCH))
> +		return -ESRCH;
> +
> +	/* find sequence number in buffer */
> +	p = buf;
> +	num = 0;
> +	while (p < (buf + len)) {
> +		if (strncmp(p, "SEQNUM=", 7) == 0) {
> +			int r;
> +
> +			p += 7;
> +			r = kstrtoull(p, 10, &num);
> +			if (r) {
> +				put_net(pns);
> +				return r;
> +			}
> +			break;
> +		}
> +		p += (strlen(p) + 1);
> +	}

Ok, that's crazy, replacing an existing sequence number with a sequence
number of the namespace?  An interesting hack, yes, but something we
want to maintain for the next 20+ years, no.  Surely there's a better
way to do this?

But again, I'm not sold on this whole idea anyway.

greg k-h