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_anon(mnt->mnt_sb);
  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_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
 106                      void *private_data)
 107 {
 108         void *ret;
 109
 110         do {
 111                 struct ns_common *ns = ns_get_cb(private_data);
 112                 if (!ns)
 113                         return ERR_PTR(-ENOENT);
 114
 115                 ret = __ns_get_path(path, ns);
 116         } while (ret == ERR_PTR(-EAGAIN));
 117
 118         return ret;
 119 }
 120
 121 struct ns_get_path_task_args {
 122         const struct proc_ns_operations *ns_ops;
 123         struct task_struct *task;
 124 };
 125
 126 static struct ns_common *ns_get_path_task(void *private_data)
 127 {
 128         struct ns_get_path_task_args *args = private_data;
 129
 130         return args->ns_ops->get(args->task);
 131 }
 132
 133 void *ns_get_path(struct path *path, struct task_struct *task,
 134                   const struct proc_ns_operations *ns_ops)
 135 {
 136         struct ns_get_path_task_args args = {
 137                 .ns_ops = ns_ops,
 138                 .task   = task,
 139         };
 140
 141         return ns_get_path_cb(path, ns_get_path_task, &args);
 142 }
 143
 144 int open_related_ns(struct ns_common *ns,
 145                    struct ns_common *(*get_ns)(struct ns_common *ns))
 146 {
 147         struct path path = {};
 148         struct file *f;
 149         void *err;
 150         int fd;
 151
 152         fd = get_unused_fd_flags(O_CLOEXEC);
 153         if (fd < 0)
 154                 return fd;
 155
 156         do {
 157                 struct ns_common *relative;
 158
 159                 relative = get_ns(ns);
 160                 if (IS_ERR(relative)) {
 161                         put_unused_fd(fd);
 162                         return PTR_ERR(relative);
 163                 }
 164
 165                 err = __ns_get_path(&path, relative);
 166         } while (err == ERR_PTR(-EAGAIN));
 167
 168         if (IS_ERR(err)) {
 169                 put_unused_fd(fd);
 170                 return PTR_ERR(err);
 171         }
 172
 173         f = dentry_open(&path, O_RDONLY, current_cred());
 174         path_put(&path);
 175         if (IS_ERR(f)) {
 176                 put_unused_fd(fd);
 177                 fd = PTR_ERR(f);
 178         } else
 179                 fd_install(fd, f);
 180
 181         return fd;
 182 }
 183 EXPORT_SYMBOL_GPL(open_related_ns);
 184
 185 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 186                         unsigned long arg)
 187 {
 188         struct user_namespace *user_ns;
 189         struct ns_common *ns = get_proc_ns(file_inode(filp));
 190         uid_t __user *argp;
 191         uid_t uid;
 192
 193         switch (ioctl) {
 194         case NS_GET_USERNS:
 195                 return open_related_ns(ns, ns_get_owner);
 196         case NS_GET_PARENT:
 197                 if (!ns->ops->get_parent)
 198                         return -EINVAL;
 199                 return open_related_ns(ns, ns->ops->get_parent);
 200         case NS_GET_NSTYPE:
 201                 return ns->ops->type;
 202         case NS_GET_OWNER_UID:
 203                 if (ns->ops->type != CLONE_NEWUSER)
 204                         return -EINVAL;
 205                 user_ns = container_of(ns, struct user_namespace, ns);
 206                 argp = (uid_t __user *) arg;
 207                 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
 208                 return put_user(uid, argp);
 209         default:
 210                 return -ENOTTY;
 211         }
 212 }
 213
 214 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 215                         const struct proc_ns_operations *ns_ops)
 216 {
 217         struct ns_common *ns;
 218         int res = -ENOENT;
 219         const char *name;
 220         ns = ns_ops->get(task);
 221         if (ns) {
 222                 name = ns_ops->real_ns_name ? : ns_ops->name;
 223                 res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
 224                 ns_ops->put(ns);
 225         }
 226         return res;
 227 }
 228
 229 struct file *proc_ns_fget(int fd)
 230 {
 231         struct file *file;
 232
 233         file = fget(fd);
 234         if (!file)
 235                 return ERR_PTR(-EBADF);
 236
 237         if (file->f_op != &ns_file_operations)
 238                 goto out_invalid;
 239
 240         return file;
 241
 242 out_invalid:
 243         fput(file);
 244         return ERR_PTR(-EINVAL);
 245 }
 246
 247 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 248 {
 249         struct inode *inode = d_inode(dentry);
 250         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 251
 252         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 253         return 0;
 254 }
 255
 256 static const struct super_operations nsfs_ops = {
 257         .statfs = simple_statfs,
 258         .evict_inode = nsfs_evict,
 259         .show_path = nsfs_show_path,
 260 };
 261 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 262                         int flags, const char *dev_name, void *data)
 263 {
 264         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 265                         &ns_dentry_operations, NSFS_MAGIC);
 266 }
 267 static struct file_system_type nsfs = {
 268         .name = "nsfs",
 269         .mount = nsfs_mount,
 270         .kill_sb = kill_anon_super,
 271 };
 272
 273 void __init nsfs_init(void)
 274 {
 275         nsfs_mnt = kern_mount(&nsfs);
 276         if (IS_ERR(nsfs_mnt))
 277                 panic("can't set nsfs up\n");
 278         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 279 }