xref: /openbmc/linux/fs/afs/dynroot.c (revision 37b9b9a5) 
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 (dentry->d_name.len >= AFSNAMEMAX) {
140 		_leave(" = -ENAMETOOLONG");
141 		return ERR_PTR(-ENAMETOOLONG);
142 	}
143 
144 	if (dentry->d_name.len == 5 &&
145 	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
146 		return afs_lookup_atcell(dentry);
147 
148 	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
149 }
150 
151 const struct inode_operations afs_dynroot_inode_operations = {
152 	.lookup		= afs_dynroot_lookup,
153 };
154 
155 /*
156  * Dirs in the dynamic root don't need revalidation.
157  */
158 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
159 {
160 	return 1;
161 }
162 
163 /*
164  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
165  * sleep)
166  * - called from dput() when d_count is going to 0.
167  * - return 1 to request dentry be unhashed, 0 otherwise
168  */
169 static int afs_dynroot_d_delete(const struct dentry *dentry)
170 {
171 	return d_really_is_positive(dentry);
172 }
173 
174 const struct dentry_operations afs_dynroot_dentry_operations = {
175 	.d_revalidate	= afs_dynroot_d_revalidate,
176 	.d_delete	= afs_dynroot_d_delete,
177 	.d_release	= afs_d_release,
178 	.d_automount	= afs_d_automount,
179 };
180 
181 /*
182  * Create a manually added cell mount directory.
183  * - The caller must hold net->proc_cells_lock
184  */
185 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
186 {
187 	struct super_block *sb = net->dynroot_sb;
188 	struct dentry *root, *subdir;
189 	int ret;
190 
191 	if (!sb || atomic_read(&sb->s_active) == 0)
192 		return 0;
193 
194 	/* Let the ->lookup op do the creation */
195 	root = sb->s_root;
196 	inode_lock(root->d_inode);
197 	subdir = lookup_one_len(cell->name, root, cell->name_len);
198 	if (IS_ERR(subdir)) {
199 		ret = PTR_ERR(subdir);
200 		goto unlock;
201 	}
202 
203 	/* Note that we're retaining an extra ref on the dentry */
204 	subdir->d_fsdata = (void *)1UL;
205 	ret = 0;
206 unlock:
207 	inode_unlock(root->d_inode);
208 	return ret;
209 }
210 
211 /*
212  * Remove a manually added cell mount directory.
213  * - The caller must hold net->proc_cells_lock
214  */
215 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
216 {
217 	struct super_block *sb = net->dynroot_sb;
218 	struct dentry *root, *subdir;
219 
220 	if (!sb || atomic_read(&sb->s_active) == 0)
221 		return;
222 
223 	root = sb->s_root;
224 	inode_lock(root->d_inode);
225 
226 	/* Don't want to trigger a lookup call, which will re-add the cell */
227 	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
228 	if (IS_ERR_OR_NULL(subdir)) {
229 		_debug("lookup %ld", PTR_ERR(subdir));
230 		goto no_dentry;
231 	}
232 
233 	_debug("rmdir %pd %u", subdir, d_count(subdir));
234 
235 	if (subdir->d_fsdata) {
236 		_debug("unpin %u", d_count(subdir));
237 		subdir->d_fsdata = NULL;
238 		dput(subdir);
239 	}
240 	dput(subdir);
241 no_dentry:
242 	inode_unlock(root->d_inode);
243 	_leave("");
244 }
245 
246 /*
247  * Populate a newly created dynamic root with cell names.
248  */
249 int afs_dynroot_populate(struct super_block *sb)
250 {
251 	struct afs_cell *cell;
252 	struct afs_net *net = afs_sb2net(sb);
253 	int ret;
254 
255 	mutex_lock(&net->proc_cells_lock);
256 
257 	net->dynroot_sb = sb;
258 	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
259 		ret = afs_dynroot_mkdir(net, cell);
260 		if (ret < 0)
261 			goto error;
262 	}
263 
264 	ret = 0;
265 out:
266 	mutex_unlock(&net->proc_cells_lock);
267 	return ret;
268 
269 error:
270 	net->dynroot_sb = NULL;
271 	goto out;
272 }
273 
274 /*
275  * When a dynamic root that's in the process of being destroyed, depopulate it
276  * of pinned directories.
277  */
278 void afs_dynroot_depopulate(struct super_block *sb)
279 {
280 	struct afs_net *net = afs_sb2net(sb);
281 	struct dentry *root = sb->s_root, *subdir, *tmp;
282 
283 	/* Prevent more subdirs from being created */
284 	mutex_lock(&net->proc_cells_lock);
285 	if (net->dynroot_sb == sb)
286 		net->dynroot_sb = NULL;
287 	mutex_unlock(&net->proc_cells_lock);
288 
289 	inode_lock(root->d_inode);
290 
291 	/* Remove all the pins for dirs created for manually added cells */
292 	list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
293 		if (subdir->d_fsdata) {
294 			subdir->d_fsdata = NULL;
295 			dput(subdir);
296 		}
297 	}
298 
299 	inode_unlock(root->d_inode);
300 }
301