fs/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_fs.h>
   7 #include <linux/proc_ns.h>
   8 #include <linux/magic.h>
   9 #include <linux/ktime.h>
  10 #include <linux/seq_file.h>
  11 #include <linux/user_namespace.h>
  12 #include <linux/nsfs.h>
  13 #include <linux/uaccess.h>
  14
  15 #include "internal.h"
  16
  17 static struct vfsmount *nsfs_mnt;
  18
  19 static long ns_ioctl(struct file *filp, unsigned int ioctl,
  20                         unsigned long arg);
  21 static const struct file_operations ns_file_operations = {
  22         .llseek         = no_llseek,
  23         .unlocked_ioctl = ns_ioctl,
  24         .compat_ioctl   = compat_ptr_ioctl,
  25 };
  26
  27 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  28 {
  29         struct inode *inode = d_inode(dentry);
  30         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  31
  32         return dynamic_dname(buffer, buflen, "%s:[%lu]",
  33                 ns_ops->name, inode->i_ino);
  34 }
  35
  36 static void ns_prune_dentry(struct dentry *dentry)
  37 {
  38         struct inode *inode = d_inode(dentry);
  39         if (inode) {
  40                 struct ns_common *ns = inode->i_private;
  41                 atomic_long_set(&ns->stashed, 0);
  42         }
  43 }
  44
  45 const struct dentry_operations ns_dentry_operations =
  46 {
  47         .d_prune        = ns_prune_dentry,
  48         .d_delete       = always_delete_dentry,
  49         .d_dname        = ns_dname,
  50 };
  51
  52 static void nsfs_evict(struct inode *inode)
  53 {
  54         struct ns_common *ns = inode->i_private;
  55         clear_inode(inode);
  56         ns->ops->put(ns);
  57 }
  58
  59 static int __ns_get_path(struct path *path, struct ns_common *ns)
  60 {
  61         struct vfsmount *mnt = nsfs_mnt;
  62         struct dentry *dentry;
  63         struct inode *inode;
  64         unsigned long d;
  65
  66         rcu_read_lock();
  67         d = atomic_long_read(&ns->stashed);
  68         if (!d)
  69                 goto slow;
  70         dentry = (struct dentry *)d;
  71         if (!lockref_get_not_dead(&dentry->d_lockref))
  72                 goto slow;
  73         rcu_read_unlock();
  74         ns->ops->put(ns);
  75 got_it:
  76         path->mnt = mntget(mnt);
  77         path->dentry = dentry;
  78         return 0;
  79 slow:
  80         rcu_read_unlock();
  81         inode = new_inode_pseudo(mnt->mnt_sb);
  82         if (!inode) {
  83                 ns->ops->put(ns);
  84                 return -ENOMEM;
  85         }
  86         inode->i_ino = ns->inum;
  87         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  88         inode->i_flags |= S_IMMUTABLE;
  89         inode->i_mode = S_IFREG | S_IRUGO;
  90         inode->i_fop = &ns_file_operations;
  91         inode->i_private = ns;
  92
  93         dentry = d_alloc_anon(mnt->mnt_sb);
  94         if (!dentry) {
  95                 iput(inode);
  96                 return -ENOMEM;
  97         }
  98         d_instantiate(dentry, inode);
  99         dentry->d_fsdata = (void *)ns->ops;
 100         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
 101         if (d) {
 102                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
 103                 dput(dentry);
 104                 cpu_relax();
 105                 return -EAGAIN;
 106         }
 107         goto got_it;
 108 }
 109
 110 int ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
 111                      void *private_data)
 112 {
 113         int ret;
 114
 115         do {
 116                 struct ns_common *ns = ns_get_cb(private_data);
 117                 if (!ns)
 118                         return -ENOENT;
 119                 ret = __ns_get_path(path, ns);
 120         } while (ret == -EAGAIN);
 121
 122         return ret;
 123 }
 124
 125 struct ns_get_path_task_args {
 126         const struct proc_ns_operations *ns_ops;
 127         struct task_struct *task;
 128 };
 129
 130 static struct ns_common *ns_get_path_task(void *private_data)
 131 {
 132         struct ns_get_path_task_args *args = private_data;
 133
 134         return args->ns_ops->get(args->task);
 135 }
 136
 137 int ns_get_path(struct path *path, struct task_struct *task,
 138                   const struct proc_ns_operations *ns_ops)
 139 {
 140         struct ns_get_path_task_args args = {
 141                 .ns_ops = ns_ops,
 142                 .task   = task,
 143         };
 144
 145         return ns_get_path_cb(path, ns_get_path_task, &args);
 146 }
 147
 148 int open_related_ns(struct ns_common *ns,
 149                    struct ns_common *(*get_ns)(struct ns_common *ns))
 150 {
 151         struct path path = {};
 152         struct file *f;
 153         int err;
 154         int fd;
 155
 156         fd = get_unused_fd_flags(O_CLOEXEC);
 157         if (fd < 0)
 158                 return fd;
 159
 160         do {
 161                 struct ns_common *relative;
 162
 163                 relative = get_ns(ns);
 164                 if (IS_ERR(relative)) {
 165                         put_unused_fd(fd);
 166                         return PTR_ERR(relative);
 167                 }
 168
 169                 err = __ns_get_path(&path, relative);
 170         } while (err == -EAGAIN);
 171
 172         if (err) {
 173                 put_unused_fd(fd);
 174                 return 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 EXPORT_SYMBOL_GPL(open_related_ns);
 188
 189 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 190                         unsigned long arg)
 191 {
 192         struct user_namespace *user_ns;
 193         struct ns_common *ns = get_proc_ns(file_inode(filp));
 194         uid_t __user *argp;
 195         uid_t uid;
 196
 197         switch (ioctl) {
 198         case NS_GET_USERNS:
 199                 return open_related_ns(ns, ns_get_owner);
 200         case NS_GET_PARENT:
 201                 if (!ns->ops->get_parent)
 202                         return -EINVAL;
 203                 return open_related_ns(ns, ns->ops->get_parent);
 204         case NS_GET_NSTYPE:
 205                 return ns->ops->type;
 206         case NS_GET_OWNER_UID:
 207                 if (ns->ops->type != CLONE_NEWUSER)
 208                         return -EINVAL;
 209                 user_ns = container_of(ns, struct user_namespace, ns);
 210                 argp = (uid_t __user *) arg;
 211                 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
 212                 return put_user(uid, argp);
 213         default:
 214                 return -ENOTTY;
 215         }
 216 }
 217
 218 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 219                         const struct proc_ns_operations *ns_ops)
 220 {
 221         struct ns_common *ns;
 222         int res = -ENOENT;
 223         const char *name;
 224         ns = ns_ops->get(task);
 225         if (ns) {
 226                 name = ns_ops->real_ns_name ? : ns_ops->name;
 227                 res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
 228                 ns_ops->put(ns);
 229         }
 230         return res;
 231 }
 232
 233 bool proc_ns_file(const struct file *file)
 234 {
 235         return file->f_op == &ns_file_operations;
 236 }
 237
 238 struct file *proc_ns_fget(int fd)
 239 {
 240         struct file *file;
 241
 242         file = fget(fd);
 243         if (!file)
 244                 return ERR_PTR(-EBADF);
 245
 246         if (file->f_op != &ns_file_operations)
 247                 goto out_invalid;
 248
 249         return file;
 250
 251 out_invalid:
 252         fput(file);
 253         return ERR_PTR(-EINVAL);
 254 }
 255
 256 /**
 257  * ns_match() - Returns true if current namespace matches dev/ino provided.
 258  * @ns: current namespace
 259  * @dev: dev_t from nsfs that will be matched against current nsfs
 260  * @ino: ino_t from nsfs that will be matched against current nsfs
 261  *
 262  * Return: true if dev and ino matches the current nsfs.
 263  */
 264 bool ns_match(const struct ns_common *ns, dev_t dev, ino_t ino)
 265 {
 266         return (ns->inum == ino) && (nsfs_mnt->mnt_sb->s_dev == dev);
 267 }
 268
 269
 270 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 271 {
 272         struct inode *inode = d_inode(dentry);
 273         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 274
 275         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 276         return 0;
 277 }
 278
 279 static const struct super_operations nsfs_ops = {
 280         .statfs = simple_statfs,
 281         .evict_inode = nsfs_evict,
 282         .show_path = nsfs_show_path,
 283 };
 284
 285 static int nsfs_init_fs_context(struct fs_context *fc)
 286 {
 287         struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
 288         if (!ctx)
 289                 return -ENOMEM;
 290         ctx->ops = &nsfs_ops;
 291         ctx->dops = &ns_dentry_operations;
 292         return 0;
 293 }
 294
 295 static struct file_system_type nsfs = {
 296         .name = "nsfs",
 297         .init_fs_context = nsfs_init_fs_context,
 298         .kill_sb = kill_anon_super,
 299 };
 300
 301 void __init nsfs_init(void)
 302 {
 303         nsfs_mnt = kern_mount(&nsfs);
 304         if (IS_ERR(nsfs_mnt))
 305                 panic("can't set nsfs up\n");
 306         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 307 }