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         simple_inode_init_ts(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_make_root(inode);    /* not the normal use, but... */
  94         if (!dentry)
  95                 return -ENOMEM;
  96         dentry->d_fsdata = (void *)ns->ops;
  97         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
  98         if (d) {
  99                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
 100                 dput(dentry);
 101                 cpu_relax();
 102                 return -EAGAIN;
 103         }
 104         goto got_it;
 105 }
 106
 107 int ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
 108                      void *private_data)
 109 {
 110         int ret;
 111
 112         do {
 113                 struct ns_common *ns = ns_get_cb(private_data);
 114                 if (!ns)
 115                         return -ENOENT;
 116                 ret = __ns_get_path(path, ns);
 117         } while (ret == -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 int 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         int 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 == -EAGAIN);
 168
 169         if (err) {
 170                 put_unused_fd(fd);
 171                 return 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 bool proc_ns_file(const struct file *file)
 231 {
 232         return file->f_op == &ns_file_operations;
 233 }
 234
 235 /**
 236  * ns_match() - Returns true if current namespace matches dev/ino provided.
 237  * @ns: current namespace
 238  * @dev: dev_t from nsfs that will be matched against current nsfs
 239  * @ino: ino_t from nsfs that will be matched against current nsfs
 240  *
 241  * Return: true if dev and ino matches the current nsfs.
 242  */
 243 bool ns_match(const struct ns_common *ns, dev_t dev, ino_t ino)
 244 {
 245         return (ns->inum == ino) && (nsfs_mnt->mnt_sb->s_dev == dev);
 246 }
 247
 248
 249 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 250 {
 251         struct inode *inode = d_inode(dentry);
 252         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 253
 254         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 255         return 0;
 256 }
 257
 258 static const struct super_operations nsfs_ops = {
 259         .statfs = simple_statfs,
 260         .evict_inode = nsfs_evict,
 261         .show_path = nsfs_show_path,
 262 };
 263
 264 static int nsfs_init_fs_context(struct fs_context *fc)
 265 {
 266         struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
 267         if (!ctx)
 268                 return -ENOMEM;
 269         ctx->ops = &nsfs_ops;
 270         ctx->dops = &ns_dentry_operations;
 271         return 0;
 272 }
 273
 274 static struct file_system_type nsfs = {
 275         .name = "nsfs",
 276         .init_fs_context = nsfs_init_fs_context,
 277         .kill_sb = kill_anon_super,
 278 };
 279
 280 void __init nsfs_init(void)
 281 {
 282         nsfs_mnt = kern_mount(&nsfs);
 283         if (IS_ERR(nsfs_mnt))
 284                 panic("can't set nsfs up\n");
 285         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 286 }