pid namespaces: make proc have multiple superblocks - one for each namespace

Each pid namespace have to be visible through its own proc mount.  Thus we
need to have per-namespace proc trees with their own superblocks.

We cannot easily show different pid namespace via one global proc tree, since
each pid refers to different tasks in different namespaces.  E.g.  pid 1
refers to the init task in the initial namespace and to some other task when
seeing from another namespace.  Moreover - pid, exisintg in one namespace may
not exist in the other.

This approach has one move advantage is that the tasks from the init namespace
can see what tasks live in another namespace by reading entries from another
proc tree.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 63 insertions, 4 deletions

diff --git a/fs/proc/root.c b/fs/proc/root.c
index cf3046638b09..94e9d734384e 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -18,32 +18,90 @@
 #include <linux/bitops.h>
 #include <linux/smp_lock.h>
 #include <linux/mount.h>
+#include <linux/pid_namespace.h>
 
 #include "internal.h"
 
 struct proc_dir_entry *proc_bus, *proc_root_fs, *proc_root_driver;
 
+static int proc_test_super(struct super_block *sb, void *data)
+{
+        return sb->s_fs_info == data;
+}
+
+static int proc_set_super(struct super_block *sb, void *data)
+{
+        struct pid_namespace *ns;
+
+        ns = (struct pid_namespace *)data;
+        sb->s_fs_info = get_pid_ns(ns);
+        return set_anon_super(sb, NULL);
+}
+
 static int proc_get_sb(struct file_system_type *fs_type,
         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 {
+        int err;
+        struct super_block *sb;
+        struct pid_namespace *ns;
+        struct proc_inode *ei;
+
         if (proc_mnt) {
                 /* Seed the root directory with a pid so it doesn't need
                  * to be special in base.c.  I would do this earlier but
                  * the only task alive when /proc is mounted the first time
                  * is the init_task and it doesn't have any pids.
                  */
-                struct proc_inode *ei;
                 ei = PROC_I(proc_mnt->mnt_sb->s_root->d_inode);
                 if (!ei->pid)
                         ei->pid = find_get_pid(1);
         }
-        return get_sb_single(fs_type, flags, data, proc_fill_super, mnt);
+
+        if (flags & MS_KERNMOUNT)
+                ns = (struct pid_namespace *)data;
+        else
+                ns = current->nsproxy->pid_ns;
+
+        sb = sget(fs_type, proc_test_super, proc_set_super, ns);
+        if (IS_ERR(sb))
+                return PTR_ERR(sb);
+
+        if (!sb->s_root) {
+                sb->s_flags = flags;
+                err = proc_fill_super(sb);
+                if (err) {
+                        up_write(&sb->s_umount);
+                        deactivate_super(sb);
+                        return err;
+                }
+
+                ei = PROC_I(sb->s_root->d_inode);
+                if (!ei->pid) {
+                        rcu_read_lock();
+                        ei->pid = get_pid(find_pid_ns(1, ns));
+                        rcu_read_unlock();
+                }
+
+                sb->s_flags |= MS_ACTIVE;
+                ns->proc_mnt = mnt;
+        }
+
+        return simple_set_mnt(mnt, sb);
+}
+
+static void proc_kill_sb(struct super_block *sb)
+{
+        struct pid_namespace *ns;
+
+        ns = (struct pid_namespace *)sb->s_fs_info;
+        kill_anon_super(sb);
+        put_pid_ns(ns);
 }
 
 static struct file_system_type proc_fs_type = {
         .name           = "proc",
         .get_sb         = proc_get_sb,
-        .kill_sb        = kill_anon_super,
+        .kill_sb        = proc_kill_sb,
 };
 
 void __init proc_root_init(void)
@@ -54,12 +112,13 @@ void __init proc_root_init(void)
         err = register_filesystem(&proc_fs_type);
         if (err)
                 return;
-        proc_mnt = kern_mount(&proc_fs_type);
+        proc_mnt = kern_mount_data(&proc_fs_type, &init_pid_ns);
         err = PTR_ERR(proc_mnt);
         if (IS_ERR(proc_mnt)) {
                 unregister_filesystem(&proc_fs_type);
                 return;
         }
+
         proc_misc_init();
 
         proc_net_init();