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

[Oren Laadan <orenl-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org>]

On Wed, Sep 9, 2015 at 2:53 PM, Michael J. Coss <
michael.coss-cfy2TCaE7SFv+uJa97DSA9BPR1lH4CV8@public.gmane.org> 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-cfy2TCaE7SFv+uJa97DSA9BPR1lH4CV8@public.gmane.org>
> ---
>  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
>
>  #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);
> +       }
> +
> +       /* if we didn't see a valid seqnum, or none was present, return
> error */
> +       if (num == 0) {
> +               put_net(pns);
> +               return -EINVAL;
> +       }
> +       /* update per namespace sequence number as needed */
> +       if (pns->kevent_seqnum < num)
> +               pns->kevent_seqnum = num;
> +
> +       list_for_each_entry(ue_sk, &uevent_sock_list, list) {
> +               struct sock *uevent_sock = ue_sk->sk;
> +               struct sk_buff *skb;
> +
> +               if (!netlink_has_listeners(uevent_sock, 1))
> +                       continue;
> +               /*
> +                * only send to sockets share the same network namespace
> +                * as the passed pid
> +                */
> +               if (!net_eq(sock_net(uevent_sock), pns))
> +                       continue;
> +
> +               /* allocate message with the maximum possible size */
> +               skb = alloc_skb(len, GFP_KERNEL);
> +               if (skb) {
> +                       char *p;
> +
> +                       p = skb_put(skb, len);
> +                       memcpy(p, buf, len);
> +                       NETLINK_CB(skb).dst_group = 1;
> +                       retval = netlink_broadcast(uevent_sock, skb, 0, 1,
> +                                                  GFP_KERNEL);
> +
> +                       /* ENOBUFS should be handled in userspace */
> +                       if (retval == -ENOBUFS || retval == -ESRCH)
> +                               retval = 0;
>

This may mask an error from an earlier send (to a distinct listener
socket). Instead, we should retain and report either the first error seen
or some error seen.



> +               } else {
> +                       retval = -ENOMEM;
> +               }
> +       }
> +       put_net(pns);
> +#endif
> +       return retval;
>
+}
> +EXPORT_SYMBOL_GPL(kobject_uevent_forward);
> +#endif
> +
>  /**
>   * add_uevent_var - add key value string to the environment buffer
>   * @env: environment buffer structure
> --
> 2.4.6
>
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