xref: /openbmc/linux/fs/afs/dynroot.c (revision a44d924c)
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, "srv=1", 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}, {%llx:%llu}",
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  	hlist_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  }
311