xref: /openbmc/linux/fs/afs/dynroot.c (revision 4e95bc26) 
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 const struct file_operations afs_dynroot_file_operations = {
14 	.open		= dcache_dir_open,
15 	.release	= dcache_dir_close,
16 	.iterate_shared	= dcache_readdir,
17 	.llseek		= dcache_dir_lseek,
18 };
19 
20 /*
21  * Probe to see if a cell may exist.  This prevents positive dentries from
22  * being created unnecessarily.
23  */
24 static int afs_probe_cell_name(struct dentry *dentry)
25 {
26 	struct afs_cell *cell;
27 	const char *name = dentry->d_name.name;
28 	size_t len = dentry->d_name.len;
29 	int ret;
30 
31 	/* Names prefixed with a dot are R/W mounts. */
32 	if (name[0] == '.') {
33 		if (len == 1)
34 			return -EINVAL;
35 		name++;
36 		len--;
37 	}
38 
39 	cell = afs_lookup_cell_rcu(afs_d2net(dentry), name, len);
40 	if (!IS_ERR(cell)) {
41 		afs_put_cell(afs_d2net(dentry), cell);
42 		return 0;
43 	}
44 
45 	ret = dns_query("afsdb", name, len, "srv=1", NULL, NULL, false);
46 	if (ret == -ENODATA)
47 		ret = -EDESTADDRREQ;
48 	return ret;
49 }
50 
51 /*
52  * Try to auto mount the mountpoint with pseudo directory, if the autocell
53  * operation is setted.
54  */
55 struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
56 {
57 	struct afs_vnode *vnode = AFS_FS_I(dir);
58 	struct inode *inode;
59 	int ret = -ENOENT;
60 
61 	_enter("%p{%pd}, {%llx:%llu}",
62 	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
63 
64 	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
65 		goto out;
66 
67 	ret = afs_probe_cell_name(dentry);
68 	if (ret < 0)
69 		goto out;
70 
71 	inode = afs_iget_pseudo_dir(dir->i_sb, false);
72 	if (IS_ERR(inode)) {
73 		ret = PTR_ERR(inode);
74 		goto out;
75 	}
76 
77 	_leave("= %p", inode);
78 	return inode;
79 
80 out:
81 	_leave("= %d", ret);
82 	return ret == -ENOENT ? NULL : ERR_PTR(ret);
83 }
84 
85 /*
86  * Look up @cell in a dynroot directory.  This is a substitution for the
87  * local cell name for the net namespace.
88  */
89 static struct dentry *afs_lookup_atcell(struct dentry *dentry)
90 {
91 	struct afs_cell *cell;
92 	struct afs_net *net = afs_d2net(dentry);
93 	struct dentry *ret;
94 	unsigned int seq = 0;
95 	char *name;
96 	int len;
97 
98 	if (!net->ws_cell)
99 		return ERR_PTR(-ENOENT);
100 
101 	ret = ERR_PTR(-ENOMEM);
102 	name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
103 	if (!name)
104 		goto out_p;
105 
106 	rcu_read_lock();
107 	do {
108 		read_seqbegin_or_lock(&net->cells_lock, &seq);
109 		cell = rcu_dereference_raw(net->ws_cell);
110 		if (cell) {
111 			len = cell->name_len;
112 			memcpy(name, cell->name, len + 1);
113 		}
114 	} while (need_seqretry(&net->cells_lock, seq));
115 	done_seqretry(&net->cells_lock, seq);
116 	rcu_read_unlock();
117 
118 	ret = ERR_PTR(-ENOENT);
119 	if (!cell)
120 		goto out_n;
121 
122 	ret = lookup_one_len(name, dentry->d_parent, len);
123 
124 	/* We don't want to d_add() the @cell dentry here as we don't want to
125 	 * the cached dentry to hide changes to the local cell name.
126 	 */
127 
128 out_n:
129 	kfree(name);
130 out_p:
131 	return ret;
132 }
133 
134 /*
135  * Look up an entry in a dynroot directory.
136  */
137 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
138 					 unsigned int flags)
139 {
140 	_enter("%pd", dentry);
141 
142 	ASSERTCMP(d_inode(dentry), ==, NULL);
143 
144 	if (dentry->d_name.len >= AFSNAMEMAX) {
145 		_leave(" = -ENAMETOOLONG");
146 		return ERR_PTR(-ENAMETOOLONG);
147 	}
148 
149 	if (dentry->d_name.len == 5 &&
150 	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
151 		return afs_lookup_atcell(dentry);
152 
153 	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
154 }
155 
156 const struct inode_operations afs_dynroot_inode_operations = {
157 	.lookup		= afs_dynroot_lookup,
158 };
159 
160 /*
161  * Dirs in the dynamic root don't need revalidation.
162  */
163 static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
164 {
165 	return 1;
166 }
167 
168 /*
169  * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
170  * sleep)
171  * - called from dput() when d_count is going to 0.
172  * - return 1 to request dentry be unhashed, 0 otherwise
173  */
174 static int afs_dynroot_d_delete(const struct dentry *dentry)
175 {
176 	return d_really_is_positive(dentry);
177 }
178 
179 const struct dentry_operations afs_dynroot_dentry_operations = {
180 	.d_revalidate	= afs_dynroot_d_revalidate,
181 	.d_delete	= afs_dynroot_d_delete,
182 	.d_release	= afs_d_release,
183 	.d_automount	= afs_d_automount,
184 };
185 
186 /*
187  * Create a manually added cell mount directory.
188  * - The caller must hold net->proc_cells_lock
189  */
190 int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
191 {
192 	struct super_block *sb = net->dynroot_sb;
193 	struct dentry *root, *subdir;
194 	int ret;
195 
196 	if (!sb || atomic_read(&sb->s_active) == 0)
197 		return 0;
198 
199 	/* Let the ->lookup op do the creation */
200 	root = sb->s_root;
201 	inode_lock(root->d_inode);
202 	subdir = lookup_one_len(cell->name, root, cell->name_len);
203 	if (IS_ERR(subdir)) {
204 		ret = PTR_ERR(subdir);
205 		goto unlock;
206 	}
207 
208 	/* Note that we're retaining an extra ref on the dentry */
209 	subdir->d_fsdata = (void *)1UL;
210 	ret = 0;
211 unlock:
212 	inode_unlock(root->d_inode);
213 	return ret;
214 }
215 
216 /*
217  * Remove a manually added cell mount directory.
218  * - The caller must hold net->proc_cells_lock
219  */
220 void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
221 {
222 	struct super_block *sb = net->dynroot_sb;
223 	struct dentry *root, *subdir;
224 
225 	if (!sb || atomic_read(&sb->s_active) == 0)
226 		return;
227 
228 	root = sb->s_root;
229 	inode_lock(root->d_inode);
230 
231 	/* Don't want to trigger a lookup call, which will re-add the cell */
232 	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
233 	if (IS_ERR_OR_NULL(subdir)) {
234 		_debug("lookup %ld", PTR_ERR(subdir));
235 		goto no_dentry;
236 	}
237 
238 	_debug("rmdir %pd %u", subdir, d_count(subdir));
239 
240 	if (subdir->d_fsdata) {
241 		_debug("unpin %u", d_count(subdir));
242 		subdir->d_fsdata = NULL;
243 		dput(subdir);
244 	}
245 	dput(subdir);
246 no_dentry:
247 	inode_unlock(root->d_inode);
248 	_leave("");
249 }
250 
251 /*
252  * Populate a newly created dynamic root with cell names.
253  */
254 int afs_dynroot_populate(struct super_block *sb)
255 {
256 	struct afs_cell *cell;
257 	struct afs_net *net = afs_sb2net(sb);
258 	int ret;
259 
260 	mutex_lock(&net->proc_cells_lock);
261 
262 	net->dynroot_sb = sb;
263 	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
264 		ret = afs_dynroot_mkdir(net, cell);
265 		if (ret < 0)
266 			goto error;
267 	}
268 
269 	ret = 0;
270 out:
271 	mutex_unlock(&net->proc_cells_lock);
272 	return ret;
273 
274 error:
275 	net->dynroot_sb = NULL;
276 	goto out;
277 }
278 
279 /*
280  * When a dynamic root that's in the process of being destroyed, depopulate it
281  * of pinned directories.
282  */
283 void afs_dynroot_depopulate(struct super_block *sb)
284 {
285 	struct afs_net *net = afs_sb2net(sb);
286 	struct dentry *root = sb->s_root, *subdir, *tmp;
287 
288 	/* Prevent more subdirs from being created */
289 	mutex_lock(&net->proc_cells_lock);
290 	if (net->dynroot_sb == sb)
291 		net->dynroot_sb = NULL;
292 	mutex_unlock(&net->proc_cells_lock);
293 
294 	inode_lock(root->d_inode);
295 
296 	/* Remove all the pins for dirs created for manually added cells */
297 	list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
298 		if (subdir->d_fsdata) {
299 			subdir->d_fsdata = NULL;
300 			dput(subdir);
301 		}
302 	}
303 
304 	inode_unlock(root->d_inode);
305 }
306