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>

18 files changed, 132 insertions, 12 deletions

diff --git a/fs/mount.h b/fs/mount.h
index 630fafc616bb..cd5007980400 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -4,6 +4,7 @@
 
 struct mnt_namespace {
         atomic_t                count;
+        unsigned int            proc_inum;
         struct mount *  root;
         struct list_head        list;
         struct user_namespace   *user_ns;
diff --git a/fs/namespace.c b/fs/namespace.c
index cab78a74aca3..c1bbe86f4920 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2301,6 +2301,7 @@ dput_out:
 
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
+        proc_free_inum(ns->proc_inum);
         put_user_ns(ns->user_ns);
         kfree(ns);
 }
@@ -2317,10 +2318,16 @@ static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 {
         struct mnt_namespace *new_ns;
+        int ret;
 
         new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
         if (!new_ns)
                 return ERR_PTR(-ENOMEM);
+        ret = proc_alloc_inum(&new_ns->proc_inum);
+        if (ret) {
+                kfree(new_ns);
+                return ERR_PTR(ret);
+        }
         new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
         atomic_set(&new_ns->count, 1);
         new_ns->root = NULL;
@@ -2799,10 +2806,17 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns)
         return 0;
 }
 
+static unsigned int mntns_inum(void *ns)
+{
+        struct mnt_namespace *mnt_ns = ns;
+        return mnt_ns->proc_inum;
+}
+
 const struct proc_ns_operations mntns_operations = {
         .name           = "mnt",
         .type           = CLONE_NEWNS,
         .get            = mntns_get,
         .put            = mntns_put,
         .install        = mntns_install,
+        .inum           = mntns_inum,
 };
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 7a6d8d69cdb8..b7a47196c8c3 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -82,7 +82,7 @@ static struct dentry *proc_ns_get_dentry(struct super_block *sb,
                 return ERR_PTR(-ENOMEM);
         }
 
-        inode = new_inode(sb);
+        inode = iget_locked(sb, ns_ops->inum(ns));
         if (!inode) {
                 dput(dentry);
                 ns_ops->put(ns);
@@ -90,13 +90,17 @@ static struct dentry *proc_ns_get_dentry(struct super_block *sb,
         }
 
         ei = PROC_I(inode);
-        inode->i_ino = get_next_ino();
-        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
-        inode->i_op = &ns_inode_operations;
-        inode->i_mode = S_IFREG | S_IRUGO;
-        inode->i_fop = &ns_file_operations;
-        ei->ns_ops = ns_ops;
-        ei->ns = ns;
+        if (inode->i_state & I_NEW) {
+                inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+                inode->i_op = &ns_inode_operations;
+                inode->i_mode = S_IFREG | S_IRUGO;
+                inode->i_fop = &ns_file_operations;
+                ei->ns_ops = ns_ops;
+                ei->ns = ns;
+                unlock_new_inode(inode);
+        } else {
+                ns_ops->put(ns);
+        }
 
         d_set_d_op(dentry, &ns_dentry_operations);
         result = d_instantiate_unique(dentry, inode);
@@ -162,12 +166,12 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
         if (!ns)
                 goto out_put_task;
 
-        snprintf(name, sizeof(name), "%s", ns_ops->name);
+        snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns_ops->inum(ns));
         len = strlen(name);
 
         if (len > buflen)
                 len = buflen;
-        if (copy_to_user(buffer, ns_ops->name, len))
+        if (copy_to_user(buffer, name, len))
                 len = -EFAULT;
 
         ns_ops->put(ns);
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index f03af702a39d..fe771978e877 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -67,6 +67,8 @@ struct ipc_namespace {
 
         /* user_ns which owns the ipc ns */
         struct user_namespace *user_ns;
+
+        unsigned int    proc_inum;
 };
 
 extern struct ipc_namespace init_ipc_ns;
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 4c96acdb2489..bf285999273a 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -37,6 +37,7 @@ struct pid_namespace {
         kgid_t pid_gid;
         int hide_pid;
         int reboot;     /* group exit code if this pidns was rebooted */
+        unsigned int proc_inum;
 };
 
 extern struct pid_namespace init_pid_ns;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index bf1d000fbba6..2e24018b7cec 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -28,7 +28,11 @@ struct mm_struct;
  */
 
 enum {
-        PROC_ROOT_INO = 1,
+        PROC_ROOT_INO           = 1,
+        PROC_IPC_INIT_INO       = 0xEFFFFFFFU,
+        PROC_UTS_INIT_INO       = 0xEFFFFFFEU,
+        PROC_USER_INIT_INO      = 0xEFFFFFFDU,
+        PROC_PID_INIT_INO       = 0xEFFFFFFCU,
 };
 
 /*
@@ -263,6 +267,7 @@ struct proc_ns_operations {
         void *(*get)(struct task_struct *task);
         void (*put)(void *ns);
         int (*install)(struct nsproxy *nsproxy, void *ns);
+        unsigned int (*inum)(void *ns);
 };
 extern const struct proc_ns_operations netns_operations;
 extern const struct proc_ns_operations utsns_operations;
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 17651f08d67f..b9bd2e6c73cc 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -25,6 +25,7 @@ struct user_namespace {
         struct user_namespace   *parent;
         kuid_t                  owner;
         kgid_t                  group;
+        unsigned int            proc_inum;
 };
 
 extern struct user_namespace init_user_ns;
diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index 221f4a0a7502..239e27733d6c 100644
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -23,6 +23,7 @@ struct uts_namespace {
         struct kref kref;
         struct new_utsname name;
         struct user_namespace *user_ns;
+        unsigned int proc_inum;
 };
 extern struct uts_namespace init_uts_ns;
 
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index c5a43f56b796..de644bcd8613 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -56,6 +56,8 @@ struct net {
 
         struct user_namespace   *user_ns;       /* Owning user namespace */
 
+        unsigned int            proc_inum;
+
         struct proc_dir_entry   *proc_net;
         struct proc_dir_entry   *proc_net_stat;
 
diff --git a/init/version.c b/init/version.c
index 86fe0ccb997a..58170f18912d 100644
--- a/init/version.c
+++ b/init/version.c
@@ -12,6 +12,7 @@
 #include <linux/utsname.h>
 #include <generated/utsrelease.h>
 #include <linux/version.h>
+#include <linux/proc_fs.h>
 
 #ifndef CONFIG_KALLSYMS
 #define version(a) Version_ ## a
@@ -34,6 +35,7 @@ struct uts_namespace init_uts_ns = {
                 .domainname     = UTS_DOMAINNAME,
         },
         .user_ns = &init_user_ns,
+        .proc_inum = PROC_UTS_INIT_INO,
 };
 EXPORT_SYMBOL_GPL(init_uts_ns);
 
diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index 26143d377c95..6471f1bdae96 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -16,6 +16,7 @@
 #include <linux/msg.h>
 #include <linux/ipc_namespace.h>
 #include <linux/utsname.h>
+#include <linux/proc_fs.h>
 #include <asm/uaccess.h>
 
 #include "util.h"
@@ -30,6 +31,7 @@ DEFINE_SPINLOCK(mq_lock);
 struct ipc_namespace init_ipc_ns = {
         .count          = ATOMIC_INIT(1),
         .user_ns = &init_user_ns,
+        .proc_inum = PROC_IPC_INIT_INO,
 };
 
 atomic_t nr_ipc_ns = ATOMIC_INIT(1);
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,
 };
diff --git a/kernel/pid.c b/kernel/pid.c
index 6e8da291de49..3026ddae0a34 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 68508d330634..560da0dab230 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 750acffbe9ec..33acb5e53a5f 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 89f6eaed067a..f5975ccf9348 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 fdc619eb61ef..f6336d51d64c 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,
 };
-
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