fs/afs/dynroot.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* AFS dynamic root handling
   3  *
   4  * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/fs.h>
   9 #include <linux/namei.h>
  10 #include <linux/dns_resolver.h>
  11 #include "internal.h"
  12
  13 static atomic_t afs_autocell_ino;
  14
  15 /*
  16  * iget5() comparator for inode created by autocell operations
  17  *
  18  * These pseudo inodes don't match anything.
  19  */
  20 static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
  21 {
  22         return 0;
  23 }
  24
  25 /*
  26  * iget5() inode initialiser
  27  */
  28 static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
  29 {
  30         struct afs_super_info *as = AFS_FS_S(inode->i_sb);
  31         struct afs_vnode *vnode = AFS_FS_I(inode);
  32         struct afs_fid *fid = opaque;
  33
  34         vnode->volume           = as->volume;
  35         vnode->fid              = *fid;
  36         inode->i_ino            = fid->vnode;
  37         inode->i_generation     = fid->unique;
  38         return 0;
  39 }
  40
  41 /*
  42  * Create an inode for a dynamic root directory or an autocell dynamic
  43  * automount dir.
  44  */
  45 struct inode *afs_iget_pseudo_dir(struct super_block *sb, bool root)
  46 {
  47         struct afs_super_info *as = AFS_FS_S(sb);
  48         struct afs_vnode *vnode;
  49         struct inode *inode;
  50         struct afs_fid fid = {};
  51
  52         _enter("");
  53
  54         if (as->volume)
  55                 fid.vid = as->volume->vid;
  56         if (root) {
  57                 fid.vnode = 1;
  58                 fid.unique = 1;
  59         } else {
  60                 fid.vnode = atomic_inc_return(&afs_autocell_ino);
  61                 fid.unique = 0;
  62         }
  63
  64         inode = iget5_locked(sb, fid.vnode,
  65                              afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
  66         if (!inode) {
  67                 _leave(" = -ENOMEM");
  68                 return ERR_PTR(-ENOMEM);
  69         }
  70
  71         _debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
  72                inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);
  73
  74         vnode = AFS_FS_I(inode);
  75
  76         /* there shouldn't be an existing inode */
  77         BUG_ON(!(inode->i_state & I_NEW));
  78
  79         inode->i_size           = 0;
  80         inode->i_mode           = S_IFDIR | S_IRUGO | S_IXUGO;
  81         if (root) {
  82                 inode->i_op     = &afs_dynroot_inode_operations;
  83                 inode->i_fop    = &simple_dir_operations;
  84         } else {
  85                 inode->i_op     = &afs_autocell_inode_operations;
  86         }
  87         set_nlink(inode, 2);
  88         inode->i_uid            = GLOBAL_ROOT_UID;
  89         inode->i_gid            = GLOBAL_ROOT_GID;
  90         inode->i_ctime = inode->i_atime = inode->i_mtime = current_time(inode);
  91         inode->i_blocks         = 0;
  92         inode->i_generation     = 0;
  93
  94         set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
  95         if (!root) {
  96                 set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
  97                 inode->i_flags |= S_AUTOMOUNT;
  98         }
  99
 100         inode->i_flags |= S_NOATIME;
 101         unlock_new_inode(inode);
 102         _leave(" = %p", inode);
 103         return inode;
 104 }
 105
 106 /*
 107  * Probe to see if a cell may exist.  This prevents positive dentries from
 108  * being created unnecessarily.
 109  */
 110 static int afs_probe_cell_name(struct dentry *dentry)
 111 {
 112         struct afs_cell *cell;
 113         struct afs_net *net = afs_d2net(dentry);
 114         const char *name = dentry->d_name.name;
 115         size_t len = dentry->d_name.len;
 116         int ret;
 117
 118         /* Names prefixed with a dot are R/W mounts. */
 119         if (name[0] == '.') {
 120                 if (len == 1)
 121                         return -EINVAL;
 122                 name++;
 123                 len--;
 124         }
 125
 126         cell = afs_lookup_cell_rcu(net, name, len);
 127         if (!IS_ERR(cell)) {
 128                 afs_put_cell(net, cell);
 129                 return 0;
 130         }
 131
 132         ret = dns_query(net->net, "afsdb", name, len, "srv=1",
 133                         NULL, NULL, false);
 134         if (ret == -ENODATA)
 135                 ret = -EDESTADDRREQ;
 136         return ret;
 137 }
 138
 139 /*
 140  * Try to auto mount the mountpoint with pseudo directory, if the autocell
 141  * operation is setted.
 142  */
 143 struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
 144 {
 145         struct afs_vnode *vnode = AFS_FS_I(dir);
 146         struct inode *inode;
 147         int ret = -ENOENT;
 148
 149         _enter("%p{%pd}, {%llx:%llu}",
 150                dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
 151
 152         if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
 153                 goto out;
 154
 155         ret = afs_probe_cell_name(dentry);
 156         if (ret < 0)
 157                 goto out;
 158
 159         inode = afs_iget_pseudo_dir(dir->i_sb, false);
 160         if (IS_ERR(inode)) {
 161                 ret = PTR_ERR(inode);
 162                 goto out;
 163         }
 164
 165         _leave("= %p", inode);
 166         return inode;
 167
 168 out:
 169         _leave("= %d", ret);
 170         return ret == -ENOENT ? NULL : ERR_PTR(ret);
 171 }
 172
 173 /*
 174  * Look up @cell in a dynroot directory.  This is a substitution for the
 175  * local cell name for the net namespace.
 176  */
 177 static struct dentry *afs_lookup_atcell(struct dentry *dentry)
 178 {
 179         struct afs_cell *cell;
 180         struct afs_net *net = afs_d2net(dentry);
 181         struct dentry *ret;
 182         unsigned int seq = 0;
 183         char *name;
 184         int len;
 185
 186         if (!net->ws_cell)
 187                 return ERR_PTR(-ENOENT);
 188
 189         ret = ERR_PTR(-ENOMEM);
 190         name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
 191         if (!name)
 192                 goto out_p;
 193
 194         rcu_read_lock();
 195         do {
 196                 read_seqbegin_or_lock(&net->cells_lock, &seq);
 197                 cell = rcu_dereference_raw(net->ws_cell);
 198                 if (cell) {
 199                         len = cell->name_len;
 200                         memcpy(name, cell->name, len + 1);
 201                 }
 202         } while (need_seqretry(&net->cells_lock, seq));
 203         done_seqretry(&net->cells_lock, seq);
 204         rcu_read_unlock();
 205
 206         ret = ERR_PTR(-ENOENT);
 207         if (!cell)
 208                 goto out_n;
 209
 210         ret = lookup_one_len(name, dentry->d_parent, len);
 211
 212         /* We don't want to d_add() the @cell dentry here as we don't want to
 213          * the cached dentry to hide changes to the local cell name.
 214          */
 215
 216 out_n:
 217         kfree(name);
 218 out_p:
 219         return ret;
 220 }
 221
 222 /*
 223  * Look up an entry in a dynroot directory.
 224  */
 225 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
 226                                          unsigned int flags)
 227 {
 228         _enter("%pd", dentry);
 229
 230         ASSERTCMP(d_inode(dentry), ==, NULL);
 231
 232         if (flags & LOOKUP_CREATE)
 233                 return ERR_PTR(-EOPNOTSUPP);
 234
 235         if (dentry->d_name.len >= AFSNAMEMAX) {
 236                 _leave(" = -ENAMETOOLONG");
 237                 return ERR_PTR(-ENAMETOOLONG);
 238         }
 239
 240         if (dentry->d_name.len == 5 &&
 241             memcmp(dentry->d_name.name, "@cell", 5) == 0)
 242                 return afs_lookup_atcell(dentry);
 243
 244         return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
 245 }
 246
 247 const struct inode_operations afs_dynroot_inode_operations = {
 248         .lookup         = afs_dynroot_lookup,
 249 };
 250
 251 /*
 252  * Dirs in the dynamic root don't need revalidation.
 253  */
 254 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
 255 {
 256         return 1;
 257 }
 258
 259 /*
 260  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
 261  * sleep)
 262  * - called from dput() when d_count is going to 0.
 263  * - return 1 to request dentry be unhashed, 0 otherwise
 264  */
 265 static int afs_dynroot_d_delete(const struct dentry *dentry)
 266 {
 267         return d_really_is_positive(dentry);
 268 }
 269
 270 const struct dentry_operations afs_dynroot_dentry_operations = {
 271         .d_revalidate   = afs_dynroot_d_revalidate,
 272         .d_delete       = afs_dynroot_d_delete,
 273         .d_release      = afs_d_release,
 274         .d_automount    = afs_d_automount,
 275 };
 276
 277 /*
 278  * Create a manually added cell mount directory.
 279  * - The caller must hold net->proc_cells_lock
 280  */
 281 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
 282 {
 283         struct super_block *sb = net->dynroot_sb;
 284         struct dentry *root, *subdir;
 285         int ret;
 286
 287         if (!sb || atomic_read(&sb->s_active) == 0)
 288                 return 0;
 289
 290         /* Let the ->lookup op do the creation */
 291         root = sb->s_root;
 292         inode_lock(root->d_inode);
 293         subdir = lookup_one_len(cell->name, root, cell->name_len);
 294         if (IS_ERR(subdir)) {
 295                 ret = PTR_ERR(subdir);
 296                 goto unlock;
 297         }
 298
 299         /* Note that we're retaining an extra ref on the dentry */
 300         subdir->d_fsdata = (void *)1UL;
 301         ret = 0;
 302 unlock:
 303         inode_unlock(root->d_inode);
 304         return ret;
 305 }
 306
 307 /*
 308  * Remove a manually added cell mount directory.
 309  * - The caller must hold net->proc_cells_lock
 310  */
 311 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
 312 {
 313         struct super_block *sb = net->dynroot_sb;
 314         struct dentry *root, *subdir;
 315
 316         if (!sb || atomic_read(&sb->s_active) == 0)
 317                 return;
 318
 319         root = sb->s_root;
 320         inode_lock(root->d_inode);
 321
 322         /* Don't want to trigger a lookup call, which will re-add the cell */
 323         subdir = try_lookup_one_len(cell->name, root, cell->name_len);
 324         if (IS_ERR_OR_NULL(subdir)) {
 325                 _debug("lookup %ld", PTR_ERR(subdir));
 326                 goto no_dentry;
 327         }
 328
 329         _debug("rmdir %pd %u", subdir, d_count(subdir));
 330
 331         if (subdir->d_fsdata) {
 332                 _debug("unpin %u", d_count(subdir));
 333                 subdir->d_fsdata = NULL;
 334                 dput(subdir);
 335         }
 336         dput(subdir);
 337 no_dentry:
 338         inode_unlock(root->d_inode);
 339         _leave("");
 340 }
 341
 342 /*
 343  * Populate a newly created dynamic root with cell names.
 344  */
 345 int afs_dynroot_populate(struct super_block *sb)
 346 {
 347         struct afs_cell *cell;
 348         struct afs_net *net = afs_sb2net(sb);
 349         int ret;
 350
 351         mutex_lock(&net->proc_cells_lock);
 352
 353         net->dynroot_sb = sb;
 354         hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
 355                 ret = afs_dynroot_mkdir(net, cell);
 356                 if (ret < 0)
 357                         goto error;
 358         }
 359
 360         ret = 0;
 361 out:
 362         mutex_unlock(&net->proc_cells_lock);
 363         return ret;
 364
 365 error:
 366         net->dynroot_sb = NULL;
 367         goto out;
 368 }
 369
 370 /*
 371  * When a dynamic root that's in the process of being destroyed, depopulate it
 372  * of pinned directories.
 373  */
 374 void afs_dynroot_depopulate(struct super_block *sb)
 375 {
 376         struct afs_net *net = afs_sb2net(sb);
 377         struct dentry *root = sb->s_root, *subdir, *tmp;
 378
 379         /* Prevent more subdirs from being created */
 380         mutex_lock(&net->proc_cells_lock);
 381         if (net->dynroot_sb == sb)
 382                 net->dynroot_sb = NULL;
 383         mutex_unlock(&net->proc_cells_lock);
 384
 385         inode_lock(root->d_inode);
 386
 387         /* Remove all the pins for dirs created for manually added cells */
 388         list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
 389                 if (subdir->d_fsdata) {
 390                         subdir->d_fsdata = NULL;
 391                         dput(subdir);
 392                 }
 393         }
 394
 395         inode_unlock(root->d_inode);
 396 }