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Linux/fs/afs/dynroot.c

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  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_find_cell(net, name, len, afs_cell_trace_use_probe);
127         if (!IS_ERR(cell)) {
128                 afs_unuse_cell(net, cell, afs_cell_trace_unuse_probe);
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         char *name;
183         int len;
184 
185         if (!net->ws_cell)
186                 return ERR_PTR(-ENOENT);
187 
188         ret = ERR_PTR(-ENOMEM);
189         name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
190         if (!name)
191                 goto out_p;
192 
193         down_read(&net->cells_lock);
194         cell = net->ws_cell;
195         if (cell) {
196                 len = cell->name_len;
197                 memcpy(name, cell->name, len + 1);
198         }
199         up_read(&net->cells_lock);
200 
201         ret = ERR_PTR(-ENOENT);
202         if (!cell)
203                 goto out_n;
204 
205         ret = lookup_one_len(name, dentry->d_parent, len);
206 
207         /* We don't want to d_add() the @cell dentry here as we don't want to
208          * the cached dentry to hide changes to the local cell name.
209          */
210 
211 out_n:
212         kfree(name);
213 out_p:
214         return ret;
215 }
216 
217 /*
218  * Look up an entry in a dynroot directory.
219  */
220 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
221                                          unsigned int flags)
222 {
223         _enter("%pd", dentry);
224 
225         ASSERTCMP(d_inode(dentry), ==, NULL);
226 
227         if (flags & LOOKUP_CREATE)
228                 return ERR_PTR(-EOPNOTSUPP);
229 
230         if (dentry->d_name.len >= AFSNAMEMAX) {
231                 _leave(" = -ENAMETOOLONG");
232                 return ERR_PTR(-ENAMETOOLONG);
233         }
234 
235         if (dentry->d_name.len == 5 &&
236             memcmp(dentry->d_name.name, "@cell", 5) == 0)
237                 return afs_lookup_atcell(dentry);
238 
239         return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
240 }
241 
242 const struct inode_operations afs_dynroot_inode_operations = {
243         .lookup         = afs_dynroot_lookup,
244 };
245 
246 /*
247  * Dirs in the dynamic root don't need revalidation.
248  */
249 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
250 {
251         return 1;
252 }
253 
254 /*
255  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
256  * sleep)
257  * - called from dput() when d_count is going to 0.
258  * - return 1 to request dentry be unhashed, 0 otherwise
259  */
260 static int afs_dynroot_d_delete(const struct dentry *dentry)
261 {
262         return d_really_is_positive(dentry);
263 }
264 
265 const struct dentry_operations afs_dynroot_dentry_operations = {
266         .d_revalidate   = afs_dynroot_d_revalidate,
267         .d_delete       = afs_dynroot_d_delete,
268         .d_release      = afs_d_release,
269         .d_automount    = afs_d_automount,
270 };
271 
272 /*
273  * Create a manually added cell mount directory.
274  * - The caller must hold net->proc_cells_lock
275  */
276 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
277 {
278         struct super_block *sb = net->dynroot_sb;
279         struct dentry *root, *subdir;
280         int ret;
281 
282         if (!sb || atomic_read(&sb->s_active) == 0)
283                 return 0;
284 
285         /* Let the ->lookup op do the creation */
286         root = sb->s_root;
287         inode_lock(root->d_inode);
288         subdir = lookup_one_len(cell->name, root, cell->name_len);
289         if (IS_ERR(subdir)) {
290                 ret = PTR_ERR(subdir);
291                 goto unlock;
292         }
293 
294         /* Note that we're retaining an extra ref on the dentry */
295         subdir->d_fsdata = (void *)1UL;
296         ret = 0;
297 unlock:
298         inode_unlock(root->d_inode);
299         return ret;
300 }
301 
302 /*
303  * Remove a manually added cell mount directory.
304  * - The caller must hold net->proc_cells_lock
305  */
306 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
307 {
308         struct super_block *sb = net->dynroot_sb;
309         struct dentry *root, *subdir;
310 
311         if (!sb || atomic_read(&sb->s_active) == 0)
312                 return;
313 
314         root = sb->s_root;
315         inode_lock(root->d_inode);
316 
317         /* Don't want to trigger a lookup call, which will re-add the cell */
318         subdir = try_lookup_one_len(cell->name, root, cell->name_len);
319         if (IS_ERR_OR_NULL(subdir)) {
320                 _debug("lookup %ld", PTR_ERR(subdir));
321                 goto no_dentry;
322         }
323 
324         _debug("rmdir %pd %u", subdir, d_count(subdir));
325 
326         if (subdir->d_fsdata) {
327                 _debug("unpin %u", d_count(subdir));
328                 subdir->d_fsdata = NULL;
329                 dput(subdir);
330         }
331         dput(subdir);
332 no_dentry:
333         inode_unlock(root->d_inode);
334         _leave("");
335 }
336 
337 /*
338  * Populate a newly created dynamic root with cell names.
339  */
340 int afs_dynroot_populate(struct super_block *sb)
341 {
342         struct afs_cell *cell;
343         struct afs_net *net = afs_sb2net(sb);
344         int ret;
345 
346         mutex_lock(&net->proc_cells_lock);
347 
348         net->dynroot_sb = sb;
349         hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
350                 ret = afs_dynroot_mkdir(net, cell);
351                 if (ret < 0)
352                         goto error;
353         }
354 
355         ret = 0;
356 out:
357         mutex_unlock(&net->proc_cells_lock);
358         return ret;
359 
360 error:
361         net->dynroot_sb = NULL;
362         goto out;
363 }
364 
365 /*
366  * When a dynamic root that's in the process of being destroyed, depopulate it
367  * of pinned directories.
368  */
369 void afs_dynroot_depopulate(struct super_block *sb)
370 {
371         struct afs_net *net = afs_sb2net(sb);
372         struct dentry *root = sb->s_root, *subdir, *tmp;
373 
374         /* Prevent more subdirs from being created */
375         mutex_lock(&net->proc_cells_lock);
376         if (net->dynroot_sb == sb)
377                 net->dynroot_sb = NULL;
378         mutex_unlock(&net->proc_cells_lock);
379 
380         if (root) {
381                 inode_lock(root->d_inode);
382 
383                 /* Remove all the pins for dirs created for manually added cells */
384                 list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
385                         if (subdir->d_fsdata) {
386                                 subdir->d_fsdata = NULL;
387                                 dput(subdir);
388                         }
389                 }
390 
391                 inode_unlock(root->d_inode);
392         }
393 }
394 

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