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, 16 insertions, 0 deletions

diff --git a/ipc/namespace.c b/ipc/namespace.c
index 72c868277793..cf3386a51de2 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -26,9 +26,16 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
         if (ns == NULL)
                 return ERR_PTR(-ENOMEM);
 
+        err = proc_alloc_inum(&ns->proc_inum);
+        if (err) {
+                kfree(ns);
+                return ERR_PTR(err);
+        }
+
         atomic_set(&ns->count, 1);
         err = mq_init_ns(ns);
         if (err) {
+                proc_free_inum(ns->proc_inum);
                 kfree(ns);
                 return ERR_PTR(err);
         }
@@ -111,6 +118,7 @@ static void free_ipc_ns(struct ipc_namespace *ns)
          */
         ipcns_notify(IPCNS_REMOVED);
         put_user_ns(ns->user_ns);
+        proc_free_inum(ns->proc_inum);
         kfree(ns);
 }
 
@@ -172,10 +180,18 @@ static int ipcns_install(struct nsproxy *nsproxy, void *new)
         return 0;
 }
 
+static unsigned int ipcns_inum(void *vp)
+{
+        struct ipc_namespace *ns = vp;
+
+        return ns->proc_inum;
+}
+
 const struct proc_ns_operations ipcns_operations = {
         .name           = "ipc",
         .type           = CLONE_NEWIPC,
         .get            = ipcns_get,
         .put            = ipcns_put,
         .install        = ipcns_install,
+        .inum           = ipcns_inum,
 };