xref: /openbmc/linux/fs/afs/dynroot.c (revision e7253313) 
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 /*
14  * Probe to see if a cell may exist.  This prevents positive dentries from
15  * being created unnecessarily.
16  */
17 static int afs_probe_cell_name(struct dentry *dentry)
18 {
19 	struct afs_cell *cell;
20 	struct afs_net *net = afs_d2net(dentry);
21 	const char *name = dentry->d_name.name;
22 	size_t len = dentry->d_name.len;
23 	int ret;
24 
25 	/* Names prefixed with a dot are R/W mounts. */
26 	if (name[0] == '.') {
27 		if (len == 1)
28 			return -EINVAL;
29 		name++;
30 		len--;
31 	}
32 
33 	cell = afs_lookup_cell_rcu(net, name, len);
34 	if (!IS_ERR(cell)) {
35 		afs_put_cell(net, cell);
36 		return 0;
37 	}
38 
39 	ret = dns_query(net->net, "afsdb", name, len, "srv=1",
40 			NULL, NULL, false);
41 	if (ret == -ENODATA)
42 		ret = -EDESTADDRREQ;
43 	return ret;
44 }
45 
46 /*
47  * Try to auto mount the mountpoint with pseudo directory, if the autocell
48  * operation is setted.
49  */
50 struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
51 {
52 	struct afs_vnode *vnode = AFS_FS_I(dir);
53 	struct inode *inode;
54 	int ret = -ENOENT;
55 
56 	_enter("%p{%pd}, {%llx:%llu}",
57 	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
58 
59 	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
60 		goto out;
61 
62 	ret = afs_probe_cell_name(dentry);
63 	if (ret < 0)
64 		goto out;
65 
66 	inode = afs_iget_pseudo_dir(dir->i_sb, false);
67 	if (IS_ERR(inode)) {
68 		ret = PTR_ERR(inode);
69 		goto out;
70 	}
71 
72 	_leave("= %p", inode);
73 	return inode;
74 
75 out:
76 	_leave("= %d", ret);
77 	return ret == -ENOENT ? NULL : ERR_PTR(ret);
78 }
79 
80 /*
81  * Look up @cell in a dynroot directory.  This is a substitution for the
82  * local cell name for the net namespace.
83  */
84 static struct dentry *afs_lookup_atcell(struct dentry *dentry)
85 {
86 	struct afs_cell *cell;
87 	struct afs_net *net = afs_d2net(dentry);
88 	struct dentry *ret;
89 	unsigned int seq = 0;
90 	char *name;
91 	int len;
92 
93 	if (!net->ws_cell)
94 		return ERR_PTR(-ENOENT);
95 
96 	ret = ERR_PTR(-ENOMEM);
97 	name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
98 	if (!name)
99 		goto out_p;
100 
101 	rcu_read_lock();
102 	do {
103 		read_seqbegin_or_lock(&net->cells_lock, &seq);
104 		cell = rcu_dereference_raw(net->ws_cell);
105 		if (cell) {
106 			len = cell->name_len;
107 			memcpy(name, cell->name, len + 1);
108 		}
109 	} while (need_seqretry(&net->cells_lock, seq));
110 	done_seqretry(&net->cells_lock, seq);
111 	rcu_read_unlock();
112 
113 	ret = ERR_PTR(-ENOENT);
114 	if (!cell)
115 		goto out_n;
116 
117 	ret = lookup_one_len(name, dentry->d_parent, len);
118 
119 	/* We don't want to d_add() the @cell dentry here as we don't want to
120 	 * the cached dentry to hide changes to the local cell name.
121 	 */
122 
123 out_n:
124 	kfree(name);
125 out_p:
126 	return ret;
127 }
128 
129 /*
130  * Look up an entry in a dynroot directory.
131  */
132 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
133 					 unsigned int flags)
134 {
135 	_enter("%pd", dentry);
136 
137 	ASSERTCMP(d_inode(dentry), ==, NULL);
138 
139 	if (flags & LOOKUP_CREATE)
140 		return ERR_PTR(-EOPNOTSUPP);
141 
142 	if (dentry->d_name.len >= AFSNAMEMAX) {
143 		_leave(" = -ENAMETOOLONG");
144 		return ERR_PTR(-ENAMETOOLONG);
145 	}
146 
147 	if (dentry->d_name.len == 5 &&
148 	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
149 		return afs_lookup_atcell(dentry);
150 
151 	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
152 }
153 
154 const struct inode_operations afs_dynroot_inode_operations = {
155 	.lookup		= afs_dynroot_lookup,
156 };
157 
158 /*
159  * Dirs in the dynamic root don't need revalidation.
160  */
161 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
162 {
163 	return 1;
164 }
165 
166 /*
167  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
168  * sleep)
169  * - called from dput() when d_count is going to 0.
170  * - return 1 to request dentry be unhashed, 0 otherwise
171  */
172 static int afs_dynroot_d_delete(const struct dentry *dentry)
173 {
174 	return d_really_is_positive(dentry);
175 }
176 
177 const struct dentry_operations afs_dynroot_dentry_operations = {
178 	.d_revalidate	= afs_dynroot_d_revalidate,
179 	.d_delete	= afs_dynroot_d_delete,
180 	.d_release	= afs_d_release,
181 	.d_automount	= afs_d_automount,
182 };
183 
184 /*
185  * Create a manually added cell mount directory.
186  * - The caller must hold net->proc_cells_lock
187  */
188 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
189 {
190 	struct super_block *sb = net->dynroot_sb;
191 	struct dentry *root, *subdir;
192 	int ret;
193 
194 	if (!sb || atomic_read(&sb->s_active) == 0)
195 		return 0;
196 
197 	/* Let the ->lookup op do the creation */
198 	root = sb->s_root;
199 	inode_lock(root->d_inode);
200 	subdir = lookup_one_len(cell->name, root, cell->name_len);
201 	if (IS_ERR(subdir)) {
202 		ret = PTR_ERR(subdir);
203 		goto unlock;
204 	}
205 
206 	/* Note that we're retaining an extra ref on the dentry */
207 	subdir->d_fsdata = (void *)1UL;
208 	ret = 0;
209 unlock:
210 	inode_unlock(root->d_inode);
211 	return ret;
212 }
213 
214 /*
215  * Remove a manually added cell mount directory.
216  * - The caller must hold net->proc_cells_lock
217  */
218 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
219 {
220 	struct super_block *sb = net->dynroot_sb;
221 	struct dentry *root, *subdir;
222 
223 	if (!sb || atomic_read(&sb->s_active) == 0)
224 		return;
225 
226 	root = sb->s_root;
227 	inode_lock(root->d_inode);
228 
229 	/* Don't want to trigger a lookup call, which will re-add the cell */
230 	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
231 	if (IS_ERR_OR_NULL(subdir)) {
232 		_debug("lookup %ld", PTR_ERR(subdir));
233 		goto no_dentry;
234 	}
235 
236 	_debug("rmdir %pd %u", subdir, d_count(subdir));
237 
238 	if (subdir->d_fsdata) {
239 		_debug("unpin %u", d_count(subdir));
240 		subdir->d_fsdata = NULL;
241 		dput(subdir);
242 	}
243 	dput(subdir);
244 no_dentry:
245 	inode_unlock(root->d_inode);
246 	_leave("");
247 }
248 
249 /*
250  * Populate a newly created dynamic root with cell names.
251  */
252 int afs_dynroot_populate(struct super_block *sb)
253 {
254 	struct afs_cell *cell;
255 	struct afs_net *net = afs_sb2net(sb);
256 	int ret;
257 
258 	mutex_lock(&net->proc_cells_lock);
259 
260 	net->dynroot_sb = sb;
261 	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
262 		ret = afs_dynroot_mkdir(net, cell);
263 		if (ret < 0)
264 			goto error;
265 	}
266 
267 	ret = 0;
268 out:
269 	mutex_unlock(&net->proc_cells_lock);
270 	return ret;
271 
272 error:
273 	net->dynroot_sb = NULL;
274 	goto out;
275 }
276 
277 /*
278  * When a dynamic root that's in the process of being destroyed, depopulate it
279  * of pinned directories.
280  */
281 void afs_dynroot_depopulate(struct super_block *sb)
282 {
283 	struct afs_net *net = afs_sb2net(sb);
284 	struct dentry *root = sb->s_root, *subdir, *tmp;
285 
286 	/* Prevent more subdirs from being created */
287 	mutex_lock(&net->proc_cells_lock);
288 	if (net->dynroot_sb == sb)
289 		net->dynroot_sb = NULL;
290 	mutex_unlock(&net->proc_cells_lock);
291 
292 	inode_lock(root->d_inode);
293 
294 	/* Remove all the pins for dirs created for manually added cells */
295 	list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
296 		if (subdir->d_fsdata) {
297 			subdir->d_fsdata = NULL;
298 			dput(subdir);
299 		}
300 	}
301 
302 	inode_unlock(root->d_inode);
303 }
304