proc: Usable inode numbers for the namespace file descriptors.

Assign a unique proc inode to each namespace, and use that
inode number to ensure we only allocate at most one proc
inode for every namespace in proc.

A single proc inode per namespace allows userspace to test
to see if two processes are in the same namespace.

This has been a long requested feature and only blocked because
a naive implementation would put the id in a global space and
would ultimately require having a namespace for the names of
namespaces, making migration and certain virtualization tricks
impossible.

We still don't have per superblock inode numbers for proc, which
appears necessary for application unaware checkpoint/restart and
migrations (if the application is using namespace file descriptors)
but that is now allowd by the design if it becomes important.

I have preallocated the ipc and uts initial proc inode numbers so
their structures can be statically initialized.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index ec2870b44c1f..2e9a3132b8dd 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -381,6 +381,21 @@ struct net *get_net_ns_by_pid(pid_t pid)
 }
 EXPORT_SYMBOL_GPL(get_net_ns_by_pid);
 
+static __net_init int net_ns_net_init(struct net *net)
+{
+        return proc_alloc_inum(&net->proc_inum);
+}
+
+static __net_exit void net_ns_net_exit(struct net *net)
+{
+        proc_free_inum(net->proc_inum);
+}
+
+static struct pernet_operations __net_initdata net_ns_ops = {
+        .init = net_ns_net_init,
+        .exit = net_ns_net_exit,
+};
+
 static int __init net_ns_init(void)
 {
         struct net_generic *ng;
@@ -412,6 +427,8 @@ static int __init net_ns_init(void)
 
         mutex_unlock(&net_mutex);
 
+        register_pernet_subsys(&net_ns_ops);
+
         return 0;
 }
 
@@ -640,11 +657,18 @@ static int netns_install(struct nsproxy *nsproxy, void *ns)
         return 0;
 }
 
+static unsigned int netns_inum(void *ns)
+{
+        struct net *net = ns;
+        return net->proc_inum;
+}
+
 const struct proc_ns_operations netns_operations = {
         .name           = "net",
         .type           = CLONE_NEWNET,
         .get            = netns_get,
         .put            = netns_put,
         .install        = netns_install,
+        .inum           = netns_inum,
 };
 #endif