ns: proc files for namespace naming policy.

Create files under /proc/<pid>/ns/ to allow controlling the
namespaces of a process.

This addresses three specific problems that can make namespaces hard to
work with.
- Namespaces require a dedicated process to pin them in memory.
- It is not possible to use a namespace unless you are the child
  of the original creator.
- Namespaces don't have names that userspace can use to talk about
  them.

The namespace files under /proc/<pid>/ns/ can be opened and the
file descriptor can be used to talk about a specific namespace, and
to keep the specified namespace alive.

A namespace can be kept alive by either holding the file descriptor
open or bind mounting the file someplace else.  aka:
mount --bind /proc/self/ns/net /some/filesystem/path
mount --bind /proc/self/fd/<N> /some/filesystem/path

This allows namespaces to be named with userspace policy.

It requires additional support to make use of these filedescriptors
and that will be comming in the following patches.

Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

5 files changed, 223 insertions, 11 deletions

diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index df434c5f28fb..c1c729335924 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -20,6 +20,7 @@ proc-y	+= stat.o
 proc-y  += uptime.o
 proc-y  += version.o
 proc-y  += softirqs.o
+proc-y  += namespaces.o
 proc-$(CONFIG_PROC_SYSCTL)      += proc_sysctl.o
 proc-$(CONFIG_NET)              += proc_net.o
 proc-$(CONFIG_PROC_KCORE)       += kcore.o
diff --git a/fs/proc/base.c b/fs/proc/base.c
index dfa532730e55..dc8bca72b002 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -600,7 +600,7 @@ static int proc_fd_access_allowed(struct inode *inode)
         return allowed;
 }
 
-static int proc_setattr(struct dentry *dentry, struct iattr *attr)
+int proc_setattr(struct dentry *dentry, struct iattr *attr)
 {
         int error;
         struct inode *inode = dentry->d_inode;
@@ -1736,8 +1736,7 @@ static int task_dumpable(struct task_struct *task)
         return 0;
 }
 
-
-static struct inode *proc_pid_make_inode(struct super_block * sb, struct task_struct *task)
+struct inode *proc_pid_make_inode(struct super_block * sb, struct task_struct *task)
 {
         struct inode * inode;
         struct proc_inode *ei;
@@ -1779,7 +1778,7 @@ out_unlock:
         return NULL;
 }
 
-static int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
+int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
 {
         struct inode *inode = dentry->d_inode;
         struct task_struct *task;
@@ -1820,7 +1819,7 @@ static int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat
  * made this apply to all per process world readable and executable
  * directories.
  */
-static int pid_revalidate(struct dentry *dentry, struct nameidata *nd)
+int pid_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
         struct inode *inode;
         struct task_struct *task;
@@ -1862,7 +1861,7 @@ static int pid_delete_dentry(const struct dentry * dentry)
         return !proc_pid(dentry->d_inode)->tasks[PIDTYPE_PID].first;
 }
 
-static const struct dentry_operations pid_dentry_operations =
+const struct dentry_operations pid_dentry_operations =
 {
         .d_revalidate   = pid_revalidate,
         .d_delete       = pid_delete_dentry,
@@ -1870,9 +1869,6 @@ static const struct dentry_operations pid_dentry_operations =
 
 /* Lookups */
 
-typedef struct dentry *instantiate_t(struct inode *, struct dentry *,
-                                struct task_struct *, const void *);
-
 /*
  * Fill a directory entry.
  *
@@ -1885,8 +1881,8 @@ typedef struct dentry *instantiate_t(struct inode *, struct dentry *,
  * reported by readdir in sync with the inode numbers reported
  * by stat.
  */
-static int proc_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
-        char *name, int len,
+int proc_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
+        const char *name, int len,
         instantiate_t instantiate, struct task_struct *task, const void *ptr)
 {
         struct dentry *child, *dir = filp->f_path.dentry;
@@ -2820,6 +2816,7 @@ static const struct pid_entry tgid_base_stuff[] = {
         DIR("task",       S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
         DIR("fd",         S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
         DIR("fdinfo",     S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
+        DIR("ns",         S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
 #ifdef CONFIG_NET
         DIR("net",        S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
 #endif
@@ -3168,6 +3165,7 @@ out_no_task:
 static const struct pid_entry tid_base_stuff[] = {
         DIR("fd",        S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
         DIR("fdinfo",    S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
+        DIR("ns",        S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
         REG("environ",   S_IRUSR, proc_environ_operations),
         INF("auxv",      S_IRUSR, proc_pid_auxv),
         ONE("status",    S_IRUGO, proc_pid_status),
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index d15aa1b1cc8f..74b48cfa1bb2 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -28,6 +28,7 @@ static void proc_evict_inode(struct inode *inode)
 {
         struct proc_dir_entry *de;
         struct ctl_table_header *head;
+        const struct proc_ns_operations *ns_ops;
 
         truncate_inode_pages(&inode->i_data, 0);
         end_writeback(inode);
@@ -44,6 +45,10 @@ static void proc_evict_inode(struct inode *inode)
                 rcu_assign_pointer(PROC_I(inode)->sysctl, NULL);
                 sysctl_head_put(head);
         }
+        /* Release any associated namespace */
+        ns_ops = PROC_I(inode)->ns_ops;
+        if (ns_ops && ns_ops->put)
+                ns_ops->put(PROC_I(inode)->ns);
 }
 
 static struct kmem_cache * proc_inode_cachep;
@@ -62,6 +67,8 @@ static struct inode *proc_alloc_inode(struct super_block *sb)
         ei->pde = NULL;
         ei->sysctl = NULL;
         ei->sysctl_entry = NULL;
+        ei->ns = NULL;
+        ei->ns_ops = NULL;
         inode = &ei->vfs_inode;
         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
         return inode;
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index c03e8d3a3a5b..96245a1b1a7c 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -119,3 +119,21 @@ struct inode *proc_get_inode(struct super_block *, struct proc_dir_entry *);
  */
 int proc_readdir(struct file *, void *, filldir_t);
 struct dentry *proc_lookup(struct inode *, struct dentry *, struct nameidata *);
+
+
+
+/* Lookups */
+typedef struct dentry *instantiate_t(struct inode *, struct dentry *,
+                                struct task_struct *, const void *);
+int proc_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
+        const char *name, int len,
+        instantiate_t instantiate, struct task_struct *task, const void *ptr);
+int pid_revalidate(struct dentry *dentry, struct nameidata *nd);
+struct inode *proc_pid_make_inode(struct super_block * sb, struct task_struct *task);
+extern const struct dentry_operations pid_dentry_operations;
+int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat);
+int proc_setattr(struct dentry *dentry, struct iattr *attr);
+
+extern const struct inode_operations proc_ns_dir_inode_operations;
+extern const struct file_operations proc_ns_dir_operations;
+
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
new file mode 100644
index 000000000000..6ae9f07d59ee
--- /dev/null
+++ b/fs/proc/namespaces.c
@@ -0,0 +1,188 @@
+#include <linux/proc_fs.h>
+#include <linux/nsproxy.h>
+#include <linux/sched.h>
+#include <linux/ptrace.h>
+#include <linux/fs_struct.h>
+#include <linux/mount.h>
+#include <linux/path.h>
+#include <linux/namei.h>
+#include <linux/file.h>
+#include <linux/utsname.h>
+#include <net/net_namespace.h>
+#include <linux/mnt_namespace.h>
+#include <linux/ipc_namespace.h>
+#include <linux/pid_namespace.h>
+#include "internal.h"
+
+
+static const struct proc_ns_operations *ns_entries[] = {
+};
+
+static const struct file_operations ns_file_operations = {
+        .llseek         = no_llseek,
+};
+
+static struct dentry *proc_ns_instantiate(struct inode *dir,
+        struct dentry *dentry, struct task_struct *task, const void *ptr)
+{
+        const struct proc_ns_operations *ns_ops = ptr;
+        struct inode *inode;
+        struct proc_inode *ei;
+        struct dentry *error = ERR_PTR(-ENOENT);
+
+        inode = proc_pid_make_inode(dir->i_sb, task);
+        if (!inode)
+                goto out;
+
+        ei = PROC_I(inode);
+        inode->i_mode = S_IFREG|S_IRUSR;
+        inode->i_fop  = &ns_file_operations;
+        ei->ns_ops    = ns_ops;
+        ei->ns        = ns_ops->get(task);
+        if (!ei->ns)
+                goto out_iput;
+
+        dentry->d_op = &pid_dentry_operations;
+        d_add(dentry, inode);
+        /* Close the race of the process dying before we return the dentry */
+        if (pid_revalidate(dentry, NULL))
+                error = NULL;
+out:
+        return error;
+out_iput:
+        iput(inode);
+        goto out;
+}
+
+static int proc_ns_fill_cache(struct file *filp, void *dirent,
+        filldir_t filldir, struct task_struct *task,
+        const struct proc_ns_operations *ops)
+{
+        return proc_fill_cache(filp, dirent, filldir,
+                                ops->name, strlen(ops->name),
+                                proc_ns_instantiate, task, ops);
+}
+
+static int proc_ns_dir_readdir(struct file *filp, void *dirent,
+                                filldir_t filldir)
+{
+        int i;
+        struct dentry *dentry = filp->f_path.dentry;
+        struct inode *inode = dentry->d_inode;
+        struct task_struct *task = get_proc_task(inode);
+        const struct proc_ns_operations **entry, **last;
+        ino_t ino;
+        int ret;
+
+        ret = -ENOENT;
+        if (!task)
+                goto out_no_task;
+
+        ret = -EPERM;
+        if (!ptrace_may_access(task, PTRACE_MODE_READ))
+                goto out;
+
+        ret = 0;
+        i = filp->f_pos;
+        switch (i) {
+        case 0:
+                ino = inode->i_ino;
+                if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
+                        goto out;
+                i++;
+                filp->f_pos++;
+                /* fall through */
+        case 1:
+                ino = parent_ino(dentry);
+                if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
+                        goto out;
+                i++;
+                filp->f_pos++;
+                /* fall through */
+        default:
+                i -= 2;
+                if (i >= ARRAY_SIZE(ns_entries)) {
+                        ret = 1;
+                        goto out;
+                }
+                entry = ns_entries + i;
+                last = &ns_entries[ARRAY_SIZE(ns_entries) - 1];
+                while (entry <= last) {
+                        if (proc_ns_fill_cache(filp, dirent, filldir,
+                                                task, *entry) < 0)
+                                goto out;
+                        filp->f_pos++;
+                        entry++;
+                }
+        }
+
+        ret = 1;
+out:
+        put_task_struct(task);
+out_no_task:
+        return ret;
+}
+
+const struct file_operations proc_ns_dir_operations = {
+        .read           = generic_read_dir,
+        .readdir        = proc_ns_dir_readdir,
+};
+
+static struct dentry *proc_ns_dir_lookup(struct inode *dir,
+                                struct dentry *dentry, struct nameidata *nd)
+{
+        struct dentry *error;
+        struct task_struct *task = get_proc_task(dir);
+        const struct proc_ns_operations **entry, **last;
+        unsigned int len = dentry->d_name.len;
+
+        error = ERR_PTR(-ENOENT);
+
+        if (!task)
+                goto out_no_task;
+
+        error = ERR_PTR(-EPERM);
+        if (!ptrace_may_access(task, PTRACE_MODE_READ))
+                goto out;
+
+        last = &ns_entries[ARRAY_SIZE(ns_entries) - 1];
+        for (entry = ns_entries; entry <= last; entry++) {
+                if (strlen((*entry)->name) != len)
+                        continue;
+                if (!memcmp(dentry->d_name.name, (*entry)->name, len))
+                        break;
+        }
+        if (entry > last)
+                goto out;
+
+        error = proc_ns_instantiate(dir, dentry, task, *entry);
+out:
+        put_task_struct(task);
+out_no_task:
+        return error;
+}
+
+const struct inode_operations proc_ns_dir_inode_operations = {
+        .lookup         = proc_ns_dir_lookup,
+        .getattr        = pid_getattr,
+        .setattr        = proc_setattr,
+};
+
+struct file *proc_ns_fget(int fd)
+{
+        struct file *file;
+
+        file = fget(fd);
+        if (!file)
+                return ERR_PTR(-EBADF);
+
+        if (file->f_op != &ns_file_operations)
+                goto out_invalid;
+
+        return file;
+
+out_invalid:
+        fput(file);
+        return ERR_PTR(-EINVAL);
+}
+