fs/nsfs.c

   1 #include <linux/mount.h>
   2 #include <linux/file.h>
   3 #include <linux/fs.h>
   4 #include <linux/proc_ns.h>
   5 #include <linux/magic.h>
   6 #include <linux/ktime.h>
   7 #include <linux/seq_file.h>
   8 #include <linux/user_namespace.h>
   9 #include <linux/nsfs.h>
  10
  11 static struct vfsmount *nsfs_mnt;
  12
  13 static long ns_ioctl(struct file *filp, unsigned int ioctl,
  14                         unsigned long arg);
  15 static const struct file_operations ns_file_operations = {
  16         .llseek         = no_llseek,
  17         .unlocked_ioctl = ns_ioctl,
  18 };
  19
  20 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  21 {
  22         struct inode *inode = d_inode(dentry);
  23         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  24
  25         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  26                 ns_ops->name, inode->i_ino);
  27 }
  28
  29 static void ns_prune_dentry(struct dentry *dentry)
  30 {
  31         struct inode *inode = d_inode(dentry);
  32         if (inode) {
  33                 struct ns_common *ns = inode->i_private;
  34                 atomic_long_set(&ns->stashed, 0);
  35         }
  36 }
  37
  38 const struct dentry_operations ns_dentry_operations =
  39 {
  40         .d_prune        = ns_prune_dentry,
  41         .d_delete       = always_delete_dentry,
  42         .d_dname        = ns_dname,
  43 };
  44
  45 static void nsfs_evict(struct inode *inode)
  46 {
  47         struct ns_common *ns = inode->i_private;
  48         clear_inode(inode);
  49         ns->ops->put(ns);
  50 }
  51
  52 static void *__ns_get_path(struct path *path, struct ns_common *ns)
  53 {
  54         struct vfsmount *mnt = nsfs_mnt;
  55         struct qstr qname = { .name = "", };
  56         struct dentry *dentry;
  57         struct inode *inode;
  58         unsigned long d;
  59
  60         rcu_read_lock();
  61         d = atomic_long_read(&ns->stashed);
  62         if (!d)
  63                 goto slow;
  64         dentry = (struct dentry *)d;
  65         if (!lockref_get_not_dead(&dentry->d_lockref))
  66                 goto slow;
  67         rcu_read_unlock();
  68         ns->ops->put(ns);
  69 got_it:
  70         path->mnt = mntget(mnt);
  71         path->dentry = dentry;
  72         return NULL;
  73 slow:
  74         rcu_read_unlock();
  75         inode = new_inode_pseudo(mnt->mnt_sb);
  76         if (!inode) {
  77                 ns->ops->put(ns);
  78                 return ERR_PTR(-ENOMEM);
  79         }
  80         inode->i_ino = ns->inum;
  81         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  82         inode->i_flags |= S_IMMUTABLE;
  83         inode->i_mode = S_IFREG | S_IRUGO;
  84         inode->i_fop = &ns_file_operations;
  85         inode->i_private = ns;
  86
  87         dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
  88         if (!dentry) {
  89                 iput(inode);
  90                 return ERR_PTR(-ENOMEM);
  91         }
  92         d_instantiate(dentry, inode);
  93         dentry->d_flags |= DCACHE_RCUACCESS;
  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(struct path *path, struct task_struct *task,
 106                         const struct proc_ns_operations *ns_ops)
 107 {
 108         struct ns_common *ns;
 109         void *ret;
 110
 111 again:
 112         ns = ns_ops->get(task);
 113         if (!ns)
 114                 return ERR_PTR(-ENOENT);
 115
 116         ret = __ns_get_path(path, ns);
 117         if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
 118                 goto again;
 119         return ret;
 120 }
 121
 122 static int open_related_ns(struct ns_common *ns,
 123                    struct ns_common *(*get_ns)(struct ns_common *ns))
 124 {
 125         struct path path = {};
 126         struct file *f;
 127         void *err;
 128         int fd;
 129
 130         fd = get_unused_fd_flags(O_CLOEXEC);
 131         if (fd < 0)
 132                 return fd;
 133
 134         while (1) {
 135                 struct ns_common *relative;
 136
 137                 relative = get_ns(ns);
 138                 if (IS_ERR(relative)) {
 139                         put_unused_fd(fd);
 140                         return PTR_ERR(relative);
 141                 }
 142
 143                 err = __ns_get_path(&path, relative);
 144                 if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
 145                         continue;
 146                 break;
 147         }
 148         if (IS_ERR(err)) {
 149                 put_unused_fd(fd);
 150                 return PTR_ERR(err);
 151         }
 152
 153         f = dentry_open(&path, O_RDONLY, current_cred());
 154         path_put(&path);
 155         if (IS_ERR(f)) {
 156                 put_unused_fd(fd);
 157                 fd = PTR_ERR(f);
 158         } else
 159                 fd_install(fd, f);
 160
 161         return fd;
 162 }
 163
 164 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 165                         unsigned long arg)
 166 {
 167         struct ns_common *ns = get_proc_ns(file_inode(filp));
 168
 169         switch (ioctl) {
 170         case NS_GET_USERNS:
 171                 return open_related_ns(ns, ns_get_owner);
 172         case NS_GET_PARENT:
 173                 if (!ns->ops->get_parent)
 174                         return -EINVAL;
 175                 return open_related_ns(ns, ns->ops->get_parent);
 176         default:
 177                 return -ENOTTY;
 178         }
 179 }
 180
 181 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 182                         const struct proc_ns_operations *ns_ops)
 183 {
 184         struct ns_common *ns;
 185         int res = -ENOENT;
 186         ns = ns_ops->get(task);
 187         if (ns) {
 188                 res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
 189                 ns_ops->put(ns);
 190         }
 191         return res;
 192 }
 193
 194 struct file *proc_ns_fget(int fd)
 195 {
 196         struct file *file;
 197
 198         file = fget(fd);
 199         if (!file)
 200                 return ERR_PTR(-EBADF);
 201
 202         if (file->f_op != &ns_file_operations)
 203                 goto out_invalid;
 204
 205         return file;
 206
 207 out_invalid:
 208         fput(file);
 209         return ERR_PTR(-EINVAL);
 210 }
 211
 212 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 213 {
 214         struct inode *inode = d_inode(dentry);
 215         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 216
 217         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 218         return 0;
 219 }
 220
 221 static const struct super_operations nsfs_ops = {
 222         .statfs = simple_statfs,
 223         .evict_inode = nsfs_evict,
 224         .show_path = nsfs_show_path,
 225 };
 226 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 227                         int flags, const char *dev_name, void *data)
 228 {
 229         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 230                         &ns_dentry_operations, NSFS_MAGIC);
 231 }
 232 static struct file_system_type nsfs = {
 233         .name = "nsfs",
 234         .mount = nsfs_mount,
 235         .kill_sb = kill_anon_super,
 236 };
 237
 238 void __init nsfs_init(void)
 239 {
 240         nsfs_mnt = kern_mount(&nsfs);
 241         if (IS_ERR(nsfs_mnt))
 242                 panic("can't set nsfs up\n");
 243         nsfs_mnt->mnt_sb->s_flags &= ~MS_NOUSER;
 244 }