fs/afs/dynroot.c

   1 /* AFS dynamic root handling
   2  *
   3  * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/namei.h>
  14 #include <linux/dns_resolver.h>
  15 #include "internal.h"
  16
  17 const struct file_operations afs_dynroot_file_operations = {
  18         .open           = dcache_dir_open,
  19         .release        = dcache_dir_close,
  20         .iterate_shared = dcache_readdir,
  21         .llseek         = dcache_dir_lseek,
  22 };
  23
  24 /*
  25  * Probe to see if a cell may exist.  This prevents positive dentries from
  26  * being created unnecessarily.
  27  */
  28 static int afs_probe_cell_name(struct dentry *dentry)
  29 {
  30         struct afs_cell *cell;
  31         const char *name = dentry->d_name.name;
  32         size_t len = dentry->d_name.len;
  33         int ret;
  34
  35         /* Names prefixed with a dot are R/W mounts. */
  36         if (name[0] == '.') {
  37                 if (len == 1)
  38                         return -EINVAL;
  39                 name++;
  40                 len--;
  41         }
  42
  43         cell = afs_lookup_cell_rcu(afs_d2net(dentry), name, len);
  44         if (!IS_ERR(cell)) {
  45                 afs_put_cell(afs_d2net(dentry), cell);
  46                 return 0;
  47         }
  48
  49         ret = dns_query("afsdb", name, len, "", NULL, NULL);
  50         if (ret == -ENODATA)
  51                 ret = -EDESTADDRREQ;
  52         return ret;
  53 }
  54
  55 /*
  56  * Try to auto mount the mountpoint with pseudo directory, if the autocell
  57  * operation is setted.
  58  */
  59 struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
  60 {
  61         struct afs_vnode *vnode = AFS_FS_I(dir);
  62         struct inode *inode;
  63         int ret = -ENOENT;
  64
  65         _enter("%p{%pd}, {%x:%u}",
  66                dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
  67
  68         if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
  69                 goto out;
  70
  71         ret = afs_probe_cell_name(dentry);
  72         if (ret < 0)
  73                 goto out;
  74
  75         inode = afs_iget_pseudo_dir(dir->i_sb, false);
  76         if (IS_ERR(inode)) {
  77                 ret = PTR_ERR(inode);
  78                 goto out;
  79         }
  80
  81         _leave("= %p", inode);
  82         return inode;
  83
  84 out:
  85         _leave("= %d", ret);
  86         return ret == -ENOENT ? NULL : ERR_PTR(ret);
  87 }
  88
  89 /*
  90  * Look up @cell in a dynroot directory.  This is a substitution for the
  91  * local cell name for the net namespace.
  92  */
  93 static struct dentry *afs_lookup_atcell(struct dentry *dentry)
  94 {
  95         struct afs_cell *cell;
  96         struct afs_net *net = afs_d2net(dentry);
  97         struct dentry *ret;
  98         unsigned int seq = 0;
  99         char *name;
 100         int len;
 101
 102         if (!net->ws_cell)
 103                 return ERR_PTR(-ENOENT);
 104
 105         ret = ERR_PTR(-ENOMEM);
 106         name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
 107         if (!name)
 108                 goto out_p;
 109
 110         rcu_read_lock();
 111         do {
 112                 read_seqbegin_or_lock(&net->cells_lock, &seq);
 113                 cell = rcu_dereference_raw(net->ws_cell);
 114                 if (cell) {
 115                         len = cell->name_len;
 116                         memcpy(name, cell->name, len + 1);
 117                 }
 118         } while (need_seqretry(&net->cells_lock, seq));
 119         done_seqretry(&net->cells_lock, seq);
 120         rcu_read_unlock();
 121
 122         ret = ERR_PTR(-ENOENT);
 123         if (!cell)
 124                 goto out_n;
 125
 126         ret = lookup_one_len(name, dentry->d_parent, len);
 127
 128         /* We don't want to d_add() the @cell dentry here as we don't want to
 129          * the cached dentry to hide changes to the local cell name.
 130          */
 131
 132 out_n:
 133         kfree(name);
 134 out_p:
 135         return ret;
 136 }
 137
 138 /*
 139  * Look up an entry in a dynroot directory.
 140  */
 141 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
 142                                          unsigned int flags)
 143 {
 144         _enter("%pd", dentry);
 145
 146         ASSERTCMP(d_inode(dentry), ==, NULL);
 147
 148         if (dentry->d_name.len >= AFSNAMEMAX) {
 149                 _leave(" = -ENAMETOOLONG");
 150                 return ERR_PTR(-ENAMETOOLONG);
 151         }
 152
 153         if (dentry->d_name.len == 5 &&
 154             memcmp(dentry->d_name.name, "@cell", 5) == 0)
 155                 return afs_lookup_atcell(dentry);
 156
 157         return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
 158 }
 159
 160 const struct inode_operations afs_dynroot_inode_operations = {
 161         .lookup         = afs_dynroot_lookup,
 162 };
 163
 164 /*
 165  * Dirs in the dynamic root don't need revalidation.
 166  */
 167 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
 168 {
 169         return 1;
 170 }
 171
 172 /*
 173  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
 174  * sleep)
 175  * - called from dput() when d_count is going to 0.
 176  * - return 1 to request dentry be unhashed, 0 otherwise
 177  */
 178 static int afs_dynroot_d_delete(const struct dentry *dentry)
 179 {
 180         return d_really_is_positive(dentry);
 181 }
 182
 183 const struct dentry_operations afs_dynroot_dentry_operations = {
 184         .d_revalidate   = afs_dynroot_d_revalidate,
 185         .d_delete       = afs_dynroot_d_delete,
 186         .d_release      = afs_d_release,
 187         .d_automount    = afs_d_automount,
 188 };
 189
 190 /*
 191  * Create a manually added cell mount directory.
 192  * - The caller must hold net->proc_cells_lock
 193  */
 194 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
 195 {
 196         struct super_block *sb = net->dynroot_sb;
 197         struct dentry *root, *subdir;
 198         int ret;
 199
 200         if (!sb || atomic_read(&sb->s_active) == 0)
 201                 return 0;
 202
 203         /* Let the ->lookup op do the creation */
 204         root = sb->s_root;
 205         inode_lock(root->d_inode);
 206         subdir = lookup_one_len(cell->name, root, cell->name_len);
 207         if (IS_ERR(subdir)) {
 208                 ret = PTR_ERR(subdir);
 209                 goto unlock;
 210         }
 211
 212         /* Note that we're retaining an extra ref on the dentry */
 213         subdir->d_fsdata = (void *)1UL;
 214         ret = 0;
 215 unlock:
 216         inode_unlock(root->d_inode);
 217         return ret;
 218 }
 219
 220 /*
 221  * Remove a manually added cell mount directory.
 222  * - The caller must hold net->proc_cells_lock
 223  */
 224 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
 225 {
 226         struct super_block *sb = net->dynroot_sb;
 227         struct dentry *root, *subdir;
 228
 229         if (!sb || atomic_read(&sb->s_active) == 0)
 230                 return;
 231
 232         root = sb->s_root;
 233         inode_lock(root->d_inode);
 234
 235         /* Don't want to trigger a lookup call, which will re-add the cell */
 236         subdir = try_lookup_one_len(cell->name, root, cell->name_len);
 237         if (IS_ERR_OR_NULL(subdir)) {
 238                 _debug("lookup %ld", PTR_ERR(subdir));
 239                 goto no_dentry;
 240         }
 241
 242         _debug("rmdir %pd %u", subdir, d_count(subdir));
 243
 244         if (subdir->d_fsdata) {
 245                 _debug("unpin %u", d_count(subdir));
 246                 subdir->d_fsdata = NULL;
 247                 dput(subdir);
 248         }
 249         dput(subdir);
 250 no_dentry:
 251         inode_unlock(root->d_inode);
 252         _leave("");
 253 }
 254
 255 /*
 256  * Populate a newly created dynamic root with cell names.
 257  */
 258 int afs_dynroot_populate(struct super_block *sb)
 259 {
 260         struct afs_cell *cell;
 261         struct afs_net *net = afs_sb2net(sb);
 262         int ret;
 263
 264         if (mutex_lock_interruptible(&net->proc_cells_lock) < 0)
 265                 return -ERESTARTSYS;
 266
 267         net->dynroot_sb = sb;
 268         list_for_each_entry(cell, &net->proc_cells, proc_link) {
 269                 ret = afs_dynroot_mkdir(net, cell);
 270                 if (ret < 0)
 271                         goto error;
 272         }
 273
 274         ret = 0;
 275 out:
 276         mutex_unlock(&net->proc_cells_lock);
 277         return ret;
 278
 279 error:
 280         net->dynroot_sb = NULL;
 281         goto out;
 282 }
 283
 284 /*
 285  * When a dynamic root that's in the process of being destroyed, depopulate it
 286  * of pinned directories.
 287  */
 288 void afs_dynroot_depopulate(struct super_block *sb)
 289 {
 290         struct afs_net *net = afs_sb2net(sb);
 291         struct dentry *root = sb->s_root, *subdir, *tmp;
 292
 293         /* Prevent more subdirs from being created */
 294         mutex_lock(&net->proc_cells_lock);
 295         if (net->dynroot_sb == sb)
 296                 net->dynroot_sb = NULL;
 297         mutex_unlock(&net->proc_cells_lock);
 298
 299         inode_lock(root->d_inode);
 300
 301         /* Remove all the pins for dirs created for manually added cells */
 302         list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
 303                 if (subdir->d_fsdata) {
 304                         subdir->d_fsdata = NULL;
 305                         dput(subdir);
 306                 }
 307         }
 308
 309         inode_unlock(root->d_inode);
 310 }