fs/nsfs.c

   1 #include <linux/mount.h>
   2 #include <linux/file.h>
   3 #include <linux/fs.h>
   4 #include <linux/proc_ns.h>
   5 #include <linux/magic.h>
   6 #include <linux/ktime.h>
   7 #include <linux/seq_file.h>
   8 #include <linux/user_namespace.h>
   9 #include <linux/nsfs.h>
  10 #include <linux/uaccess.h>
  11
  12 static struct vfsmount *nsfs_mnt;
  13
  14 static long ns_ioctl(struct file *filp, unsigned int ioctl,
  15                         unsigned long arg);
  16 static const struct file_operations ns_file_operations = {
  17         .llseek         = no_llseek,
  18         .unlocked_ioctl = ns_ioctl,
  19 };
  20
  21 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  22 {
  23         struct inode *inode = d_inode(dentry);
  24         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  25
  26         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  27                 ns_ops->name, inode->i_ino);
  28 }
  29
  30 static void ns_prune_dentry(struct dentry *dentry)
  31 {
  32         struct inode *inode = d_inode(dentry);
  33         if (inode) {
  34                 struct ns_common *ns = inode->i_private;
  35                 atomic_long_set(&ns->stashed, 0);
  36         }
  37 }
  38
  39 const struct dentry_operations ns_dentry_operations =
  40 {
  41         .d_prune        = ns_prune_dentry,
  42         .d_delete       = always_delete_dentry,
  43         .d_dname        = ns_dname,
  44 };
  45
  46 static void nsfs_evict(struct inode *inode)
  47 {
  48         struct ns_common *ns = inode->i_private;
  49         clear_inode(inode);
  50         ns->ops->put(ns);
  51 }
  52
  53 static void *__ns_get_path(struct path *path, struct ns_common *ns)
  54 {
  55         struct vfsmount *mnt = nsfs_mnt;
  56         struct qstr qname = { .name = "", };
  57         struct dentry *dentry;
  58         struct inode *inode;
  59         unsigned long d;
  60
  61         rcu_read_lock();
  62         d = atomic_long_read(&ns->stashed);
  63         if (!d)
  64                 goto slow;
  65         dentry = (struct dentry *)d;
  66         if (!lockref_get_not_dead(&dentry->d_lockref))
  67                 goto slow;
  68         rcu_read_unlock();
  69         ns->ops->put(ns);
  70 got_it:
  71         path->mnt = mntget(mnt);
  72         path->dentry = dentry;
  73         return NULL;
  74 slow:
  75         rcu_read_unlock();
  76         inode = new_inode_pseudo(mnt->mnt_sb);
  77         if (!inode) {
  78                 ns->ops->put(ns);
  79                 return ERR_PTR(-ENOMEM);
  80         }
  81         inode->i_ino = ns->inum;
  82         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  83         inode->i_flags |= S_IMMUTABLE;
  84         inode->i_mode = S_IFREG | S_IRUGO;
  85         inode->i_fop = &ns_file_operations;
  86         inode->i_private = ns;
  87
  88         dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
  89         if (!dentry) {
  90                 iput(inode);
  91                 return ERR_PTR(-ENOMEM);
  92         }
  93         d_instantiate(dentry, inode);
  94         dentry->d_fsdata = (void *)ns->ops;
  95         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
  96         if (d) {
  97                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
  98                 dput(dentry);
  99                 cpu_relax();
 100                 return ERR_PTR(-EAGAIN);
 101         }
 102         goto got_it;
 103 }
 104
 105 void *ns_get_path(struct path *path, struct task_struct *task,
 106                         const struct proc_ns_operations *ns_ops)
 107 {
 108         struct ns_common *ns;
 109         void *ret;
 110
 111 again:
 112         ns = ns_ops->get(task);
 113         if (!ns)
 114                 return ERR_PTR(-ENOENT);
 115
 116         ret = __ns_get_path(path, ns);
 117         if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
 118                 goto again;
 119         return ret;
 120 }
 121
 122 int open_related_ns(struct ns_common *ns,
 123                    struct ns_common *(*get_ns)(struct ns_common *ns))
 124 {
 125         struct path path = {};
 126         struct file *f;
 127         void *err;
 128         int fd;
 129
 130         fd = get_unused_fd_flags(O_CLOEXEC);
 131         if (fd < 0)
 132                 return fd;
 133
 134         while (1) {
 135                 struct ns_common *relative;
 136
 137                 relative = get_ns(ns);
 138                 if (IS_ERR(relative)) {
 139                         put_unused_fd(fd);
 140                         return PTR_ERR(relative);
 141                 }
 142
 143                 err = __ns_get_path(&path, relative);
 144                 if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
 145                         continue;
 146                 break;
 147         }
 148         if (IS_ERR(err)) {
 149                 put_unused_fd(fd);
 150                 return PTR_ERR(err);
 151         }
 152
 153         f = dentry_open(&path, O_RDONLY, current_cred());
 154         path_put(&path);
 155         if (IS_ERR(f)) {
 156                 put_unused_fd(fd);
 157                 fd = PTR_ERR(f);
 158         } else
 159                 fd_install(fd, f);
 160
 161         return fd;
 162 }
 163
 164 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 165                         unsigned long arg)
 166 {
 167         struct user_namespace *user_ns;
 168         struct ns_common *ns = get_proc_ns(file_inode(filp));
 169         uid_t __user *argp;
 170         uid_t uid;
 171
 172         switch (ioctl) {
 173         case NS_GET_USERNS:
 174                 return open_related_ns(ns, ns_get_owner);
 175         case NS_GET_PARENT:
 176                 if (!ns->ops->get_parent)
 177                         return -EINVAL;
 178                 return open_related_ns(ns, ns->ops->get_parent);
 179         case NS_GET_NSTYPE:
 180                 return ns->ops->type;
 181         case NS_GET_OWNER_UID:
 182                 if (ns->ops->type != CLONE_NEWUSER)
 183                         return -EINVAL;
 184                 user_ns = container_of(ns, struct user_namespace, ns);
 185                 argp = (uid_t __user *) arg;
 186                 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
 187                 return put_user(uid, argp);
 188         default:
 189                 return -ENOTTY;
 190         }
 191 }
 192
 193 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 194                         const struct proc_ns_operations *ns_ops)
 195 {
 196         struct ns_common *ns;
 197         int res = -ENOENT;
 198         ns = ns_ops->get(task);
 199         if (ns) {
 200                 res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
 201                 ns_ops->put(ns);
 202         }
 203         return res;
 204 }
 205
 206 struct file *proc_ns_fget(int fd)
 207 {
 208         struct file *file;
 209
 210         file = fget(fd);
 211         if (!file)
 212                 return ERR_PTR(-EBADF);
 213
 214         if (file->f_op != &ns_file_operations)
 215                 goto out_invalid;
 216
 217         return file;
 218
 219 out_invalid:
 220         fput(file);
 221         return ERR_PTR(-EINVAL);
 222 }
 223
 224 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 225 {
 226         struct inode *inode = d_inode(dentry);
 227         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 228
 229         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 230         return 0;
 231 }
 232
 233 static const struct super_operations nsfs_ops = {
 234         .statfs = simple_statfs,
 235         .evict_inode = nsfs_evict,
 236         .show_path = nsfs_show_path,
 237 };
 238 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 239                         int flags, const char *dev_name, void *data)
 240 {
 241         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 242                         &ns_dentry_operations, NSFS_MAGIC);
 243 }
 244 static struct file_system_type nsfs = {
 245         .name = "nsfs",
 246         .mount = nsfs_mount,
 247         .kill_sb = kill_anon_super,
 248 };
 249
 250 void __init nsfs_init(void)
 251 {
 252         nsfs_mnt = kern_mount(&nsfs);
 253         if (IS_ERR(nsfs_mnt))
 254                 panic("can't set nsfs up\n");
 255         nsfs_mnt->mnt_sb->s_flags &= ~MS_NOUSER;
 256 }