nsfs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/mount.h>
   3 #include <linux/pseudo_fs.h>
   4 #include <linux/file.h>
   5 #include <linux/fs.h>
   6 #include <linux/proc_ns.h>
   7 #include <linux/magic.h>
   8 #include <linux/ktime.h>
   9 #include <linux/seq_file.h>
  10 #include <linux/user_namespace.h>
  11 #include <linux/nsfs.h>
  12 #include <linux/uaccess.h>
  13
  14 static struct vfsmount *nsfs_mnt;
  15
  16 static long ns_ioctl(struct file *filp, unsigned int ioctl,
  17                         unsigned long arg);
  18 static const struct file_operations ns_file_operations = {
  19         .llseek         = no_llseek,
  20         .unlocked_ioctl = ns_ioctl,
  21 };
  22
  23 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  24 {
  25         struct inode *inode = d_inode(dentry);
  26         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  27
  28         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  29                 ns_ops->name, inode->i_ino);
  30 }
  31
  32 static void ns_prune_dentry(struct dentry *dentry)
  33 {
  34         struct inode *inode = d_inode(dentry);
  35         if (inode) {
  36                 struct ns_common *ns = inode->i_private;
  37                 atomic_long_set(&ns->stashed, 0);
  38         }
  39 }
  40
  41 const struct dentry_operations ns_dentry_operations =
  42 {
  43         .d_prune        = ns_prune_dentry,
  44         .d_delete       = always_delete_dentry,
  45         .d_dname        = ns_dname,
  46 };
  47
  48 static void nsfs_evict(struct inode *inode)
  49 {
  50         struct ns_common *ns = inode->i_private;
  51         clear_inode(inode);
  52         ns->ops->put(ns);
  53 }
  54
  55 static void *__ns_get_path(struct path *path, struct ns_common *ns)
  56 {
  57         struct vfsmount *mnt = nsfs_mnt;
  58         struct dentry *dentry;
  59         struct inode *inode;
  60         unsigned long d;
  61
  62         rcu_read_lock();
  63         d = atomic_long_read(&ns->stashed);
  64         if (!d)
  65                 goto slow;
  66         dentry = (struct dentry *)d;
  67         if (!lockref_get_not_dead(&dentry->d_lockref))
  68                 goto slow;
  69         rcu_read_unlock();
  70         ns->ops->put(ns);
  71 got_it:
  72         path->mnt = mntget(mnt);
  73         path->dentry = dentry;
  74         return NULL;
  75 slow:
  76         rcu_read_unlock();
  77         inode = new_inode_pseudo(mnt->mnt_sb);
  78         if (!inode) {
  79                 ns->ops->put(ns);
  80                 return ERR_PTR(-ENOMEM);
  81         }
  82         inode->i_ino = ns->inum;
  83         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  84         inode->i_flags |= S_IMMUTABLE;
  85         inode->i_mode = S_IFREG | S_IRUGO;
  86         inode->i_fop = &ns_file_operations;
  87         inode->i_private = ns;
  88
  89         dentry = d_alloc_anon(mnt->mnt_sb);
  90         if (!dentry) {
  91                 iput(inode);
  92                 return ERR_PTR(-ENOMEM);
  93         }
  94         d_instantiate(dentry, inode);
  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         void *ret;
 110
 111         do {
 112                 struct ns_common *ns = ns_get_cb(private_data);
 113                 if (!ns)
 114                         return ERR_PTR(-ENOENT);
 115
 116                 ret = __ns_get_path(path, ns);
 117         } while (ret == ERR_PTR(-EAGAIN));
 118
 119         return ret;
 120 }
 121
 122 struct ns_get_path_task_args {
 123         const struct proc_ns_operations *ns_ops;
 124         struct task_struct *task;
 125 };
 126
 127 static struct ns_common *ns_get_path_task(void *private_data)
 128 {
 129         struct ns_get_path_task_args *args = private_data;
 130
 131         return args->ns_ops->get(args->task);
 132 }
 133
 134 void *ns_get_path(struct path *path, struct task_struct *task,
 135                   const struct proc_ns_operations *ns_ops)
 136 {
 137         struct ns_get_path_task_args args = {
 138                 .ns_ops = ns_ops,
 139                 .task   = task,
 140         };
 141
 142         return ns_get_path_cb(path, ns_get_path_task, &args);
 143 }
 144
 145 int open_related_ns(struct ns_common *ns,
 146                    struct ns_common *(*get_ns)(struct ns_common *ns))
 147 {
 148         struct path path = {};
 149         struct file *f;
 150         void *err;
 151         int fd;
 152
 153         fd = get_unused_fd_flags(O_CLOEXEC);
 154         if (fd < 0)
 155                 return fd;
 156
 157         do {
 158                 struct ns_common *relative;
 159
 160                 relative = get_ns(ns);
 161                 if (IS_ERR(relative)) {
 162                         put_unused_fd(fd);
 163                         return PTR_ERR(relative);
 164                 }
 165
 166                 err = __ns_get_path(&path, relative);
 167         } while (err == ERR_PTR(-EAGAIN));
 168
 169         if (IS_ERR(err)) {
 170                 put_unused_fd(fd);
 171                 return PTR_ERR(err);
 172         }
 173
 174         f = dentry_open(&path, O_RDONLY, current_cred());
 175         path_put(&path);
 176         if (IS_ERR(f)) {
 177                 put_unused_fd(fd);
 178                 fd = PTR_ERR(f);
 179         } else
 180                 fd_install(fd, f);
 181
 182         return fd;
 183 }
 184 EXPORT_SYMBOL_GPL(open_related_ns);
 185
 186 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 187                         unsigned long arg)
 188 {
 189         struct user_namespace *user_ns;
 190         struct ns_common *ns = get_proc_ns(file_inode(filp));
 191         uid_t __user *argp;
 192         uid_t uid;
 193
 194         switch (ioctl) {
 195         case NS_GET_USERNS:
 196                 return open_related_ns(ns, ns_get_owner);
 197         case NS_GET_PARENT:
 198                 if (!ns->ops->get_parent)
 199                         return -EINVAL;
 200                 return open_related_ns(ns, ns->ops->get_parent);
 201         case NS_GET_NSTYPE:
 202                 return ns->ops->type;
 203         case NS_GET_OWNER_UID:
 204                 if (ns->ops->type != CLONE_NEWUSER)
 205                         return -EINVAL;
 206                 user_ns = container_of(ns, struct user_namespace, ns);
 207                 argp = (uid_t __user *) arg;
 208                 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
 209                 return put_user(uid, argp);
 210         default:
 211                 return -ENOTTY;
 212         }
 213 }
 214
 215 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 216                         const struct proc_ns_operations *ns_ops)
 217 {
 218         struct ns_common *ns;
 219         int res = -ENOENT;
 220         const char *name;
 221         ns = ns_ops->get(task);
 222         if (ns) {
 223                 name = ns_ops->real_ns_name ? : ns_ops->name;
 224                 res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
 225                 ns_ops->put(ns);
 226         }
 227         return res;
 228 }
 229
 230 struct file *proc_ns_fget(int fd)
 231 {
 232         struct file *file;
 233
 234         file = fget(fd);
 235         if (!file)
 236                 return ERR_PTR(-EBADF);
 237
 238         if (file->f_op != &ns_file_operations)
 239                 goto out_invalid;
 240
 241         return file;
 242
 243 out_invalid:
 244         fput(file);
 245         return ERR_PTR(-EINVAL);
 246 }
 247
 248 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 249 {
 250         struct inode *inode = d_inode(dentry);
 251         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 252
 253         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 254         return 0;
 255 }
 256
 257 static const struct super_operations nsfs_ops = {
 258         .statfs = simple_statfs,
 259         .evict_inode = nsfs_evict,
 260         .show_path = nsfs_show_path,
 261 };
 262
 263 static int nsfs_init_fs_context(struct fs_context *fc)
 264 {
 265         struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
 266         if (!ctx)
 267                 return -ENOMEM;
 268         ctx->ops = &nsfs_ops;
 269         ctx->dops = &ns_dentry_operations;
 270         return 0;
 271 }
 272
 273 static struct file_system_type nsfs = {
 274         .name = "nsfs",
 275         .init_fs_context = nsfs_init_fs_context,
 276         .kill_sb = kill_anon_super,
 277 };
 278
 279 void __init nsfs_init(void)
 280 {
 281         nsfs_mnt = kern_mount(&nsfs);
 282         if (IS_ERR(nsfs_mnt))
 283                 panic("can't set nsfs up\n");
 284         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 285 }