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 };
  25
  26 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  27 {
  28         struct inode *inode = d_inode(dentry);
  29         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  30
  31         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  32                 ns_ops->name, inode->i_ino);
  33 }
  34
  35 static void ns_prune_dentry(struct dentry *dentry)
  36 {
  37         struct inode *inode = d_inode(dentry);
  38         if (inode) {
  39                 struct ns_common *ns = inode->i_private;
  40                 atomic_long_set(&ns->stashed, 0);
  41         }
  42 }
  43
  44 const struct dentry_operations ns_dentry_operations =
  45 {
  46         .d_prune        = ns_prune_dentry,
  47         .d_delete       = always_delete_dentry,
  48         .d_dname        = ns_dname,
  49 };
  50
  51 static void nsfs_evict(struct inode *inode)
  52 {
  53         struct ns_common *ns = inode->i_private;
  54         clear_inode(inode);
  55         ns->ops->put(ns);
  56 }
  57
  58 static void *__ns_get_path(struct path *path, struct ns_common *ns)
  59 {
  60         struct vfsmount *mnt = nsfs_mnt;
  61         struct dentry *dentry;
  62         struct inode *inode;
  63         unsigned long d;
  64
  65         rcu_read_lock();
  66         d = atomic_long_read(&ns->stashed);
  67         if (!d)
  68                 goto slow;
  69         dentry = (struct dentry *)d;
  70         if (!lockref_get_not_dead(&dentry->d_lockref))
  71                 goto slow;
  72         rcu_read_unlock();
  73         ns->ops->put(ns);
  74 got_it:
  75         path->mnt = mntget(mnt);
  76         path->dentry = dentry;
  77         return NULL;
  78 slow:
  79         rcu_read_unlock();
  80         inode = new_inode_pseudo(mnt->mnt_sb);
  81         if (!inode) {
  82                 ns->ops->put(ns);
  83                 return ERR_PTR(-ENOMEM);
  84         }
  85         inode->i_ino = ns->inum;
  86         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  87         inode->i_flags |= S_IMMUTABLE;
  88         inode->i_mode = S_IFREG | S_IRUGO;
  89         inode->i_fop = &ns_file_operations;
  90         inode->i_private = ns;
  91
  92         dentry = d_alloc_anon(mnt->mnt_sb);
  93         if (!dentry) {
  94                 iput(inode);
  95                 return ERR_PTR(-ENOMEM);
  96         }
  97         d_instantiate(dentry, inode);
  98         dentry->d_fsdata = (void *)ns->ops;
  99         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
 100         if (d) {
 101                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
 102                 dput(dentry);
 103                 cpu_relax();
 104                 return ERR_PTR(-EAGAIN);
 105         }
 106         goto got_it;
 107 }
 108
 109 void *ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
 110                      void *private_data)
 111 {
 112         void *ret;
 113
 114         do {
 115                 struct ns_common *ns = ns_get_cb(private_data);
 116                 if (!ns)
 117                         return ERR_PTR(-ENOENT);
 118
 119                 ret = __ns_get_path(path, ns);
 120         } while (ret == ERR_PTR(-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 void *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         void *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 == ERR_PTR(-EAGAIN));
 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 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 struct file *proc_ns_fget(int fd)
 234 {
 235         struct file *file;
 236
 237         file = fget(fd);
 238         if (!file)
 239                 return ERR_PTR(-EBADF);
 240
 241         if (file->f_op != &ns_file_operations)
 242                 goto out_invalid;
 243
 244         return file;
 245
 246 out_invalid:
 247         fput(file);
 248         return ERR_PTR(-EINVAL);
 249 }
 250
 251 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 252 {
 253         struct inode *inode = d_inode(dentry);
 254         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 255
 256         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 257         return 0;
 258 }
 259
 260 static const struct super_operations nsfs_ops = {
 261         .statfs = simple_statfs,
 262         .evict_inode = nsfs_evict,
 263         .show_path = nsfs_show_path,
 264 };
 265
 266 static int nsfs_init_fs_context(struct fs_context *fc)
 267 {
 268         struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
 269         if (!ctx)
 270                 return -ENOMEM;
 271         ctx->ops = &nsfs_ops;
 272         ctx->dops = &ns_dentry_operations;
 273         return 0;
 274 }
 275
 276 static struct file_system_type nsfs = {
 277         .name = "nsfs",
 278         .init_fs_context = nsfs_init_fs_context,
 279         .kill_sb = kill_anon_super,
 280 };
 281
 282 void __init nsfs_init(void)
 283 {
 284         nsfs_mnt = kern_mount(&nsfs);
 285         if (IS_ERR(nsfs_mnt))
 286                 panic("can't set nsfs up\n");
 287         nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
 288 }