fs/nsfs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/mount.h>
   3 #include <linux/file.h>
   4 #include <linux/fs.h>
   5 #include <linux/proc_ns.h>
   6 #include <linux/magic.h>
   7 #include <linux/ktime.h>
   8 #include <linux/seq_file.h>
   9 #include <linux/user_namespace.h>
  10 #include <linux/nsfs.h>
  11 #include <linux/uaccess.h>
  12
  13 static struct vfsmount *nsfs_mnt;
  14
  15 static long ns_ioctl(struct file *filp, unsigned int ioctl,
  16                         unsigned long arg);
  17 static const struct file_operations ns_file_operations = {
  18         .llseek         = no_llseek,
  19         .unlocked_ioctl = ns_ioctl,
  20 };
  21
  22 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  23 {
  24         struct inode *inode = d_inode(dentry);
  25         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  26
  27         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  28                 ns_ops->name, inode->i_ino);
  29 }
  30
  31 static void ns_prune_dentry(struct dentry *dentry)
  32 {
  33         struct inode *inode = d_inode(dentry);
  34         if (inode) {
  35                 struct ns_common *ns = inode->i_private;
  36                 atomic_long_set(&ns->stashed, 0);
  37         }
  38 }
  39
  40 const struct dentry_operations ns_dentry_operations =
  41 {
  42         .d_prune        = ns_prune_dentry,
  43         .d_delete       = always_delete_dentry,
  44         .d_dname        = ns_dname,
  45 };
  46
  47 static void nsfs_evict(struct inode *inode)
  48 {
  49         struct ns_common *ns = inode->i_private;
  50         clear_inode(inode);
  51         ns->ops->put(ns);
  52 }
  53
  54 static void *__ns_get_path(struct path *path, struct ns_common *ns)
  55 {
  56         struct vfsmount *mnt = nsfs_mnt;
  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, &empty_name);
  89         if (!dentry) {
  90                 iput(inode);
  91                 return ERR_PTR(-ENOMEM);
  92         }
  93         d_instantiate(dentry, inode);
  94         dentry->d_flags |= DCACHE_RCUACCESS;
  95         dentry->d_fsdata = (void *)ns->ops;
  96         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
  97         if (d) {
  98                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
  99                 dput(dentry);
 100                 cpu_relax();
 101                 return ERR_PTR(-EAGAIN);
 102         }
 103         goto got_it;
 104 }
 105
 106 void *ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
 107                      void *private_data)
 108 {
 109         struct ns_common *ns;
 110         void *ret;
 111
 112 again:
 113         ns = ns_get_cb(private_data);
 114         if (!ns)
 115                 return ERR_PTR(-ENOENT);
 116
 117         ret = __ns_get_path(path, ns);
 118         if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
 119                 goto again;
 120         return ret;
 121 }
 122
 123 struct ns_get_path_task_args {
 124         const struct proc_ns_operations *ns_ops;
 125         struct task_struct *task;
 126 };
 127
 128 static struct ns_common *ns_get_path_task(void *private_data)
 129 {
 130         struct ns_get_path_task_args *args = private_data;
 131
 132         return args->ns_ops->get(args->task);
 133 }
 134
 135 void *ns_get_path(struct path *path, struct task_struct *task,
 136                   const struct proc_ns_operations *ns_ops)
 137 {
 138         struct ns_get_path_task_args args = {
 139                 .ns_ops = ns_ops,
 140                 .task   = task,
 141         };
 142
 143         return ns_get_path_cb(path, ns_get_path_task, &args);
 144 }
 145
 146 int open_related_ns(struct ns_common *ns,
 147                    struct ns_common *(*get_ns)(struct ns_common *ns))
 148 {
 149         struct path path = {};
 150         struct file *f;
 151         void *err;
 152         int fd;
 153
 154         fd = get_unused_fd_flags(O_CLOEXEC);
 155         if (fd < 0)
 156                 return fd;
 157
 158         while (1) {
 159                 struct ns_common *relative;
 160
 161                 relative = get_ns(ns);
 162                 if (IS_ERR(relative)) {
 163                         put_unused_fd(fd);
 164                         return PTR_ERR(relative);
 165                 }
 166
 167                 err = __ns_get_path(&path, relative);
 168                 if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
 169                         continue;
 170                 break;
 171         }
 172         if (IS_ERR(err)) {
 173                 put_unused_fd(fd);
 174                 return PTR_ERR(err);
 175         }
 176
 177         f = dentry_open(&path, O_RDONLY, current_cred());
 178         path_put(&path);
 179         if (IS_ERR(f)) {
 180                 put_unused_fd(fd);
 181                 fd = PTR_ERR(f);
 182         } else
 183                 fd_install(fd, f);
 184
 185         return fd;
 186 }
 187
 188 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 189                         unsigned long arg)
 190 {
 191         struct user_namespace *user_ns;
 192         struct ns_common *ns = get_proc_ns(file_inode(filp));
 193         uid_t __user *argp;
 194         uid_t uid;
 195
 196         switch (ioctl) {
 197         case NS_GET_USERNS:
 198                 return open_related_ns(ns, ns_get_owner);
 199         case NS_GET_PARENT:
 200                 if (!ns->ops->get_parent)
 201                         return -EINVAL;
 202                 return open_related_ns(ns, ns->ops->get_parent);
 203         case NS_GET_NSTYPE:
 204                 return ns->ops->type;
 205         case NS_GET_OWNER_UID:
 206                 if (ns->ops->type != CLONE_NEWUSER)
 207                         return -EINVAL;
 208                 user_ns = container_of(ns, struct user_namespace, ns);
 209                 argp = (uid_t __user *) arg;
 210                 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
 211                 return put_user(uid, argp);
 212         default:
 213                 return -ENOTTY;
 214         }
 215 }
 216
 217 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 218                         const struct proc_ns_operations *ns_ops)
 219 {
 220         struct ns_common *ns;
 221         int res = -ENOENT;
 222         const char *name;
 223         ns = ns_ops->get(task);
 224         if (ns) {
 225                 name = ns_ops->real_ns_name ? : ns_ops->name;
 226                 res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
 227                 ns_ops->put(ns);
 228         }
 229         return res;
 230 }
 231
 232 struct file *proc_ns_fget(int fd)
 233 {
 234         struct file *file;
 235
 236         file = fget(fd);
 237         if (!file)
 238                 return ERR_PTR(-EBADF);
 239
 240         if (file->f_op != &ns_file_operations)
 241                 goto out_invalid;
 242
 243         return file;
 244
 245 out_invalid:
 246         fput(file);
 247         return ERR_PTR(-EINVAL);
 248 }
 249
 250 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 251 {
 252         struct inode *inode = d_inode(dentry);
 253         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 254
 255         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 256         return 0;
 257 }
 258
 259 static const struct super_operations nsfs_ops = {
 260         .statfs = simple_statfs,
 261         .evict_inode = nsfs_evict,
 262         .show_path = nsfs_show_path,
 263 };
 264 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 265                         int flags, const char *dev_name, void *data)
 266 {
 267         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 268                         &ns_dentry_operations, NSFS_MAGIC);
 269 }
 270 static struct file_system_type nsfs = {
 271         .name = "nsfs",
 272         .mount = nsfs_mount,
 273         .kill_sb = kill_anon_super,
 274 };
 275
 276 void __init nsfs_init(void)
 277 {
 278         nsfs_mnt = kern_mount(&nsfs);
 279         if (IS_ERR(nsfs_mnt))
 280                 panic("can't set nsfs up\n");
 281         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 282 }