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>

5 files changed, 46 insertions, 1 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index 6e8da291de4..3026ddae0a3 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -80,6 +80,7 @@ struct pid_namespace init_pid_ns = {
         .level = 0,
         .child_reaper = &init_task,
         .user_ns = &init_user_ns,
+        .proc_inum = PROC_PID_INIT_INO,
 };
 EXPORT_SYMBOL_GPL(init_pid_ns);
 
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 68508d33063..560da0dab23 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -107,6 +107,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
         if (ns->pid_cachep == NULL)
                 goto out_free_map;
 
+        err = proc_alloc_inum(&ns->proc_inum);
+        if (err)
+                goto out_free_map;
+
         kref_init(&ns->kref);
         ns->level = level;
         ns->parent = get_pid_ns(parent_pid_ns);
@@ -133,6 +137,7 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
 {
         int i;
 
+        proc_free_inum(ns->proc_inum);
         for (i = 0; i < PIDMAP_ENTRIES; i++)
                 kfree(ns->pidmap[i].page);
         put_user_ns(ns->user_ns);
@@ -345,12 +350,19 @@ static int pidns_install(struct nsproxy *nsproxy, void *ns)
         return 0;
 }
 
+static unsigned int pidns_inum(void *ns)
+{
+        struct pid_namespace *pid_ns = ns;
+        return pid_ns->proc_inum;
+}
+
 const struct proc_ns_operations pidns_operations = {
         .name           = "pid",
         .type           = CLONE_NEWPID,
         .get            = pidns_get,
         .put            = pidns_put,
         .install        = pidns_install,
+        .inum           = pidns_inum,
 };
 
 static __init int pid_namespaces_init(void)
diff --git a/kernel/user.c b/kernel/user.c
index 750acffbe9e..33acb5e53a5 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/export.h>
 #include <linux/user_namespace.h>
+#include <linux/proc_fs.h>
 
 /*
  * userns count is 1 for root user, 1 for init_uts_ns,
@@ -51,6 +52,7 @@ struct user_namespace init_user_ns = {
         },
         .owner = GLOBAL_ROOT_UID,
         .group = GLOBAL_ROOT_GID,
+        .proc_inum = PROC_USER_INIT_INO,
 };
 EXPORT_SYMBOL_GPL(init_user_ns);
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 89f6eaed067..f5975ccf934 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -58,6 +58,7 @@ int create_user_ns(struct cred *new)
         struct user_namespace *ns, *parent_ns = new->user_ns;
         kuid_t owner = new->euid;
         kgid_t group = new->egid;
+        int ret;
 
         /* The creator needs a mapping in the parent user namespace
          * or else we won't be able to reasonably tell userspace who
@@ -71,6 +72,12 @@ int create_user_ns(struct cred *new)
         if (!ns)
                 return -ENOMEM;
 
+        ret = proc_alloc_inum(&ns->proc_inum);
+        if (ret) {
+                kmem_cache_free(user_ns_cachep, ns);
+                return ret;
+        }
+
         kref_init(&ns->kref);
         /* Leave the new->user_ns reference with the new user namespace. */
         ns->parent = parent_ns;
@@ -103,6 +110,7 @@ void free_user_ns(struct kref *kref)
                 container_of(kref, struct user_namespace, kref);
 
         parent = ns->parent;
+        proc_free_inum(ns->proc_inum);
         kmem_cache_free(user_ns_cachep, ns);
         put_user_ns(parent);
 }
@@ -808,12 +816,19 @@ static int userns_install(struct nsproxy *nsproxy, void *ns)
         return commit_creds(cred);
 }
 
+static unsigned int userns_inum(void *ns)
+{
+        struct user_namespace *user_ns = ns;
+        return user_ns->proc_inum;
+}
+
 const struct proc_ns_operations userns_operations = {
         .name           = "user",
         .type           = CLONE_NEWUSER,
         .get            = userns_get,
         .put            = userns_put,
         .install        = userns_install,
+        .inum           = userns_inum,
 };
 
 static __init int user_namespaces_init(void)
diff --git a/kernel/utsname.c b/kernel/utsname.c
index fdc619eb61e..f6336d51d64 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -36,11 +36,18 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
                                           struct uts_namespace *old_ns)
 {
         struct uts_namespace *ns;
+        int err;
 
         ns = create_uts_ns();
         if (!ns)
                 return ERR_PTR(-ENOMEM);
 
+        err = proc_alloc_inum(&ns->proc_inum);
+        if (err) {
+                kfree(ns);
+                return ERR_PTR(err);
+        }
+
         down_read(&uts_sem);
         memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
         ns->user_ns = get_user_ns(user_ns);
@@ -77,6 +84,7 @@ void free_uts_ns(struct kref *kref)
 
         ns = container_of(kref, struct uts_namespace, kref);
         put_user_ns(ns->user_ns);
+        proc_free_inum(ns->proc_inum);
         kfree(ns);
 }
 
@@ -114,11 +122,18 @@ static int utsns_install(struct nsproxy *nsproxy, void *new)
         return 0;
 }
 
+static unsigned int utsns_inum(void *vp)
+{
+        struct uts_namespace *ns = vp;
+
+        return ns->proc_inum;
+}
+
 const struct proc_ns_operations utsns_operations = {
         .name           = "uts",
         .type           = CLONE_NEWUTS,
         .get            = utsns_get,
         .put            = utsns_put,
         .install        = utsns_install,
+        .inum           = utsns_inum,
 };
-