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_fsdata = (void *)ns->ops;
  94         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
  95         if (d) {
  96                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
  97                 dput(dentry);
  98                 cpu_relax();
  99                 return ERR_PTR(-EAGAIN);
 100         }
 101         goto got_it;
 102 }
 103
 104 void *ns_get_path(struct path *path, struct task_struct *task,
 105                         const struct proc_ns_operations *ns_ops)
 106 {
 107         struct ns_common *ns;
 108         void *ret;
 109
 110 again:
 111         ns = ns_ops->get(task);
 112         if (!ns)
 113                 return ERR_PTR(-ENOENT);
 114
 115         ret = __ns_get_path(path, ns);
 116         if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
 117                 goto again;
 118         return ret;
 119 }
 120
 121 static int open_related_ns(struct ns_common *ns,
 122                    struct ns_common *(*get_ns)(struct ns_common *ns))
 123 {
 124         struct path path = {};
 125         struct file *f;
 126         void *err;
 127         int fd;
 128
 129         fd = get_unused_fd_flags(O_CLOEXEC);
 130         if (fd < 0)
 131                 return fd;
 132
 133         while (1) {
 134                 struct ns_common *relative;
 135
 136                 relative = get_ns(ns);
 137                 if (IS_ERR(relative)) {
 138                         put_unused_fd(fd);
 139                         return PTR_ERR(relative);
 140                 }
 141
 142                 err = __ns_get_path(&path, relative);
 143                 if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
 144                         continue;
 145                 break;
 146         }
 147         if (IS_ERR(err)) {
 148                 put_unused_fd(fd);
 149                 return PTR_ERR(err);
 150         }
 151
 152         f = dentry_open(&path, O_RDONLY, current_cred());
 153         path_put(&path);
 154         if (IS_ERR(f)) {
 155                 put_unused_fd(fd);
 156                 fd = PTR_ERR(f);
 157         } else
 158                 fd_install(fd, f);
 159
 160         return fd;
 161 }
 162
 163 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 164                         unsigned long arg)
 165 {
 166         struct ns_common *ns = get_proc_ns(file_inode(filp));
 167
 168         switch (ioctl) {
 169         case NS_GET_USERNS:
 170                 return open_related_ns(ns, ns_get_owner);
 171         case NS_GET_PARENT:
 172                 if (!ns->ops->get_parent)
 173                         return -EINVAL;
 174                 return open_related_ns(ns, ns->ops->get_parent);
 175         default:
 176                 return -ENOTTY;
 177         }
 178 }
 179
 180 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 181                         const struct proc_ns_operations *ns_ops)
 182 {
 183         struct ns_common *ns;
 184         int res = -ENOENT;
 185         ns = ns_ops->get(task);
 186         if (ns) {
 187                 res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
 188                 ns_ops->put(ns);
 189         }
 190         return res;
 191 }
 192
 193 struct file *proc_ns_fget(int fd)
 194 {
 195         struct file *file;
 196
 197         file = fget(fd);
 198         if (!file)
 199                 return ERR_PTR(-EBADF);
 200
 201         if (file->f_op != &ns_file_operations)
 202                 goto out_invalid;
 203
 204         return file;
 205
 206 out_invalid:
 207         fput(file);
 208         return ERR_PTR(-EINVAL);
 209 }
 210
 211 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 212 {
 213         struct inode *inode = d_inode(dentry);
 214         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 215
 216         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 217         return 0;
 218 }
 219
 220 static const struct super_operations nsfs_ops = {
 221         .statfs = simple_statfs,
 222         .evict_inode = nsfs_evict,
 223         .show_path = nsfs_show_path,
 224 };
 225 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 226                         int flags, const char *dev_name, void *data)
 227 {
 228         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 229                         &ns_dentry_operations, NSFS_MAGIC);
 230 }
 231 static struct file_system_type nsfs = {
 232         .name = "nsfs",
 233         .mount = nsfs_mount,
 234         .kill_sb = kill_anon_super,
 235 };
 236
 237 void __init nsfs_init(void)
 238 {
 239         nsfs_mnt = kern_mount(&nsfs);
 240         if (IS_ERR(nsfs_mnt))
 241                 panic("can't set nsfs up\n");
 242         nsfs_mnt->mnt_sb->s_flags &= ~MS_NOUSER;
 243 }