xref: /openbmc/linux/fs/afs/dynroot.c (revision 38857318)
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  	netfs_inode_init(&vnode->netfs, NULL);
80  	inode->i_size		= 0;
81  	inode->i_mode		= S_IFDIR | S_IRUGO | S_IXUGO;
82  	if (root) {
83  		inode->i_op	= &afs_dynroot_inode_operations;
84  		inode->i_fop	= &simple_dir_operations;
85  	} else {
86  		inode->i_op	= &afs_autocell_inode_operations;
87  	}
88  	set_nlink(inode, 2);
89  	inode->i_uid		= GLOBAL_ROOT_UID;
90  	inode->i_gid		= GLOBAL_ROOT_GID;
91  	inode->i_ctime = inode->i_atime = inode->i_mtime = current_time(inode);
92  	inode->i_blocks		= 0;
93  	inode->i_generation	= 0;
94  
95  	set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
96  	if (!root) {
97  		set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
98  		inode->i_flags |= S_AUTOMOUNT;
99  	}
100  
101  	inode->i_flags |= S_NOATIME;
102  	unlock_new_inode(inode);
103  	_leave(" = %p", inode);
104  	return inode;
105  }
106  
107  /*
108   * Probe to see if a cell may exist.  This prevents positive dentries from
109   * being created unnecessarily.
110   */
111  static int afs_probe_cell_name(struct dentry *dentry)
112  {
113  	struct afs_cell *cell;
114  	struct afs_net *net = afs_d2net(dentry);
115  	const char *name = dentry->d_name.name;
116  	size_t len = dentry->d_name.len;
117  	int ret;
118  
119  	/* Names prefixed with a dot are R/W mounts. */
120  	if (name[0] == '.') {
121  		if (len == 1)
122  			return -EINVAL;
123  		name++;
124  		len--;
125  	}
126  
127  	cell = afs_find_cell(net, name, len, afs_cell_trace_use_probe);
128  	if (!IS_ERR(cell)) {
129  		afs_unuse_cell(net, cell, afs_cell_trace_unuse_probe);
130  		return 0;
131  	}
132  
133  	ret = dns_query(net->net, "afsdb", name, len, "srv=1",
134  			NULL, NULL, false);
135  	if (ret == -ENODATA)
136  		ret = -EDESTADDRREQ;
137  	return ret;
138  }
139  
140  /*
141   * Try to auto mount the mountpoint with pseudo directory, if the autocell
142   * operation is setted.
143   */
144  struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
145  {
146  	struct afs_vnode *vnode = AFS_FS_I(dir);
147  	struct inode *inode;
148  	int ret = -ENOENT;
149  
150  	_enter("%p{%pd}, {%llx:%llu}",
151  	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
152  
153  	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
154  		goto out;
155  
156  	ret = afs_probe_cell_name(dentry);
157  	if (ret < 0)
158  		goto out;
159  
160  	inode = afs_iget_pseudo_dir(dir->i_sb, false);
161  	if (IS_ERR(inode)) {
162  		ret = PTR_ERR(inode);
163  		goto out;
164  	}
165  
166  	_leave("= %p", inode);
167  	return inode;
168  
169  out:
170  	_leave("= %d", ret);
171  	return ret == -ENOENT ? NULL : ERR_PTR(ret);
172  }
173  
174  /*
175   * Look up @cell in a dynroot directory.  This is a substitution for the
176   * local cell name for the net namespace.
177   */
178  static struct dentry *afs_lookup_atcell(struct dentry *dentry)
179  {
180  	struct afs_cell *cell;
181  	struct afs_net *net = afs_d2net(dentry);
182  	struct dentry *ret;
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  	down_read(&net->cells_lock);
195  	cell = net->ws_cell;
196  	if (cell) {
197  		len = cell->name_len;
198  		memcpy(name, cell->name, len + 1);
199  	}
200  	up_read(&net->cells_lock);
201  
202  	ret = ERR_PTR(-ENOENT);
203  	if (!cell)
204  		goto out_n;
205  
206  	ret = lookup_one_len(name, dentry->d_parent, len);
207  
208  	/* We don't want to d_add() the @cell dentry here as we don't want to
209  	 * the cached dentry to hide changes to the local cell name.
210  	 */
211  
212  out_n:
213  	kfree(name);
214  out_p:
215  	return ret;
216  }
217  
218  /*
219   * Look up an entry in a dynroot directory.
220   */
221  static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
222  					 unsigned int flags)
223  {
224  	_enter("%pd", dentry);
225  
226  	ASSERTCMP(d_inode(dentry), ==, NULL);
227  
228  	if (flags & LOOKUP_CREATE)
229  		return ERR_PTR(-EOPNOTSUPP);
230  
231  	if (dentry->d_name.len >= AFSNAMEMAX) {
232  		_leave(" = -ENAMETOOLONG");
233  		return ERR_PTR(-ENAMETOOLONG);
234  	}
235  
236  	if (dentry->d_name.len == 5 &&
237  	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
238  		return afs_lookup_atcell(dentry);
239  
240  	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
241  }
242  
243  const struct inode_operations afs_dynroot_inode_operations = {
244  	.lookup		= afs_dynroot_lookup,
245  };
246  
247  /*
248   * Dirs in the dynamic root don't need revalidation.
249   */
250  static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
251  {
252  	return 1;
253  }
254  
255  /*
256   * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
257   * sleep)
258   * - called from dput() when d_count is going to 0.
259   * - return 1 to request dentry be unhashed, 0 otherwise
260   */
261  static int afs_dynroot_d_delete(const struct dentry *dentry)
262  {
263  	return d_really_is_positive(dentry);
264  }
265  
266  const struct dentry_operations afs_dynroot_dentry_operations = {
267  	.d_revalidate	= afs_dynroot_d_revalidate,
268  	.d_delete	= afs_dynroot_d_delete,
269  	.d_release	= afs_d_release,
270  	.d_automount	= afs_d_automount,
271  };
272  
273  /*
274   * Create a manually added cell mount directory.
275   * - The caller must hold net->proc_cells_lock
276   */
277  int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
278  {
279  	struct super_block *sb = net->dynroot_sb;
280  	struct dentry *root, *subdir;
281  	int ret;
282  
283  	if (!sb || atomic_read(&sb->s_active) == 0)
284  		return 0;
285  
286  	/* Let the ->lookup op do the creation */
287  	root = sb->s_root;
288  	inode_lock(root->d_inode);
289  	subdir = lookup_one_len(cell->name, root, cell->name_len);
290  	if (IS_ERR(subdir)) {
291  		ret = PTR_ERR(subdir);
292  		goto unlock;
293  	}
294  
295  	/* Note that we're retaining an extra ref on the dentry */
296  	subdir->d_fsdata = (void *)1UL;
297  	ret = 0;
298  unlock:
299  	inode_unlock(root->d_inode);
300  	return ret;
301  }
302  
303  /*
304   * Remove a manually added cell mount directory.
305   * - The caller must hold net->proc_cells_lock
306   */
307  void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
308  {
309  	struct super_block *sb = net->dynroot_sb;
310  	struct dentry *root, *subdir;
311  
312  	if (!sb || atomic_read(&sb->s_active) == 0)
313  		return;
314  
315  	root = sb->s_root;
316  	inode_lock(root->d_inode);
317  
318  	/* Don't want to trigger a lookup call, which will re-add the cell */
319  	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
320  	if (IS_ERR_OR_NULL(subdir)) {
321  		_debug("lookup %ld", PTR_ERR(subdir));
322  		goto no_dentry;
323  	}
324  
325  	_debug("rmdir %pd %u", subdir, d_count(subdir));
326  
327  	if (subdir->d_fsdata) {
328  		_debug("unpin %u", d_count(subdir));
329  		subdir->d_fsdata = NULL;
330  		dput(subdir);
331  	}
332  	dput(subdir);
333  no_dentry:
334  	inode_unlock(root->d_inode);
335  	_leave("");
336  }
337  
338  /*
339   * Populate a newly created dynamic root with cell names.
340   */
341  int afs_dynroot_populate(struct super_block *sb)
342  {
343  	struct afs_cell *cell;
344  	struct afs_net *net = afs_sb2net(sb);
345  	int ret;
346  
347  	mutex_lock(&net->proc_cells_lock);
348  
349  	net->dynroot_sb = sb;
350  	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
351  		ret = afs_dynroot_mkdir(net, cell);
352  		if (ret < 0)
353  			goto error;
354  	}
355  
356  	ret = 0;
357  out:
358  	mutex_unlock(&net->proc_cells_lock);
359  	return ret;
360  
361  error:
362  	net->dynroot_sb = NULL;
363  	goto out;
364  }
365  
366  /*
367   * When a dynamic root that's in the process of being destroyed, depopulate it
368   * of pinned directories.
369   */
370  void afs_dynroot_depopulate(struct super_block *sb)
371  {
372  	struct afs_net *net = afs_sb2net(sb);
373  	struct dentry *root = sb->s_root, *subdir, *tmp;
374  
375  	/* Prevent more subdirs from being created */
376  	mutex_lock(&net->proc_cells_lock);
377  	if (net->dynroot_sb == sb)
378  		net->dynroot_sb = NULL;
379  	mutex_unlock(&net->proc_cells_lock);
380  
381  	if (root) {
382  		inode_lock(root->d_inode);
383  
384  		/* Remove all the pins for dirs created for manually added cells */
385  		list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
386  			if (subdir->d_fsdata) {
387  				subdir->d_fsdata = NULL;
388  				dput(subdir);
389  			}
390  		}
391  
392  		inode_unlock(root->d_inode);
393  	}
394  }
395