proc: make proc entries inherit ownership from parent

There are certain parameters that belong to net namespace and that are
exported in /proc. They should be controllable by the container's owner,
but are currently owned by global root and thus not available.

Let's change proc code to inherit ownership of parent entry, and when
create per-ns "net" proc entry set it up as owned by container's owner.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 fs/proc/generic.c  |  2 ++
 fs/proc/proc_net.c | 13 +++++++++++++
 2 files changed, 15 insertions(+)

On Thu, Aug 4, 2016 at 8:22 PM, Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
> There are certain parameters that belong to net namespace and that are
> exported in /proc. They should be controllable by the container's owner,
> but are currently owned by global root and thus not available.
>
> Let's change proc code to inherit ownership of parent entry, and when
> create per-ns "net" proc entry set it up as owned by container's owner.
>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---

Unfortunately this blows up if !CONFIG_NET_NS because of:

commit ed160e839d2e1118529e58b04d52dba703ca629c
Author: Denis V. Lunev <den@openvz.org>
Date:   Tue Nov 13 03:23:21 2007 -0800

    [NET]: Cleanup pernet operation without CONFIG_NET_NS

    If CONFIG_NET_NS is not set, the only namespace is possible.

    This patch removes list of pernet_operations and cleanups code a bit.
    This list is not needed if there are no namespaces. We should just call
    ->init method.

    Additionally, the ->exit will be called on module unloading only. This
    case is safe - the code is not discarded. For the in/kernel code, ->exit
    should never be called.

    Signed-off-by: Denis V. Lunev <den@openvz.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>

This causes proc_net_ns_init() to be called with not-yet-initialized
init_net namespace and oops due to net->user_ns being NULL.

Unfortunately simply reverting did not appear to work. I'll figure out
what to do and resubmit.


>  fs/proc/generic.c  |  2 ++
>  fs/proc/proc_net.c | 13 +++++++++++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> index c633476..bca66d8 100644
> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -390,6 +390,8 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
>         atomic_set(&ent->count, 1);
>         spin_lock_init(&ent->pde_unload_lock);
>         INIT_LIST_HEAD(&ent->pde_openers);
> +       proc_set_user(ent, (*parent)->uid, (*parent)->gid);
> +
>  out:
>         return ent;
>  }
> diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
> index c8bbc68..d701738 100644
> --- a/fs/proc/proc_net.c
> +++ b/fs/proc/proc_net.c
> @@ -21,6 +21,7 @@
>  #include <linux/bitops.h>
>  #include <linux/mount.h>
>  #include <linux/nsproxy.h>
> +#include <linux/uidgid.h>
>  #include <net/net_namespace.h>
>  #include <linux/seq_file.h>
>
> @@ -185,6 +186,8 @@ const struct file_operations proc_net_operations = {
>  static __net_init int proc_net_ns_init(struct net *net)
>  {
>         struct proc_dir_entry *netd, *net_statd;
> +       kuid_t uid;
> +       kgid_t gid;
>         int err;
>
>         err = -ENOMEM;
> @@ -199,6 +202,16 @@ static __net_init int proc_net_ns_init(struct net *net)
>         netd->parent = &proc_root;
>         memcpy(netd->name, "net", 4);
>
> +       uid = make_kuid(net->user_ns, 0);
> +       if (!uid_valid(uid))
> +               uid = GLOBAL_ROOT_UID;
> +
> +       gid = make_kgid(net->user_ns, 0);
> +       if (!gid_valid(gid))
> +               gid = GLOBAL_ROOT_GID;
> +
> +       proc_set_user(netd, uid, gid);
> +
>         err = -EEXIST;
>         net_statd = proc_net_mkdir(net, "stat", netd);
>         if (!net_statd)
> --
> 2.8.0.rc3.226.g39d4020
>
>
> --
> Dmitry

Thanks.