1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  inode.c - securityfs
4  *
5  *  Copyright (C) 2005 Greg Kroah-Hartman <gregkh@suse.de>
6  *
7  *  Based on fs/debugfs/inode.c which had the following copyright notice:
8  *    Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
9  *    Copyright (C) 2004 IBM Inc.
10  */
11 
12 /* #define DEBUG */
13 #include <linux/sysfs.h>
14 #include <linux/kobject.h>
15 #include <linux/fs.h>
16 #include <linux/fs_context.h>
17 #include <linux/mount.h>
18 #include <linux/pagemap.h>
19 #include <linux/init.h>
20 #include <linux/namei.h>
21 #include <linux/security.h>
22 #include <linux/lsm_hooks.h>
23 #include <linux/magic.h>
24 
25 static struct vfsmount *mount;
26 static int mount_count;
27 
securityfs_free_inode(struct inode * inode)28 static void securityfs_free_inode(struct inode *inode)
29 {
30 	if (S_ISLNK(inode->i_mode))
31 		kfree(inode->i_link);
32 	free_inode_nonrcu(inode);
33 }
34 
35 static const struct super_operations securityfs_super_operations = {
36 	.statfs		= simple_statfs,
37 	.free_inode	= securityfs_free_inode,
38 };
39 
securityfs_fill_super(struct super_block * sb,struct fs_context * fc)40 static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
41 {
42 	static const struct tree_descr files[] = {{""}};
43 	int error;
44 
45 	error = simple_fill_super(sb, SECURITYFS_MAGIC, files);
46 	if (error)
47 		return error;
48 
49 	sb->s_op = &securityfs_super_operations;
50 
51 	return 0;
52 }
53 
securityfs_get_tree(struct fs_context * fc)54 static int securityfs_get_tree(struct fs_context *fc)
55 {
56 	return get_tree_single(fc, securityfs_fill_super);
57 }
58 
59 static const struct fs_context_operations securityfs_context_ops = {
60 	.get_tree	= securityfs_get_tree,
61 };
62 
securityfs_init_fs_context(struct fs_context * fc)63 static int securityfs_init_fs_context(struct fs_context *fc)
64 {
65 	fc->ops = &securityfs_context_ops;
66 	return 0;
67 }
68 
69 static struct file_system_type fs_type = {
70 	.owner =	THIS_MODULE,
71 	.name =		"securityfs",
72 	.init_fs_context = securityfs_init_fs_context,
73 	.kill_sb =	kill_litter_super,
74 };
75 
76 /**
77  * securityfs_create_dentry - create a dentry in the securityfs filesystem
78  *
79  * @name: a pointer to a string containing the name of the file to create.
80  * @mode: the permission that the file should have
81  * @parent: a pointer to the parent dentry for this file.  This should be a
82  *          directory dentry if set.  If this parameter is %NULL, then the
83  *          file will be created in the root of the securityfs filesystem.
84  * @data: a pointer to something that the caller will want to get to later
85  *        on.  The inode.i_private pointer will point to this value on
86  *        the open() call.
87  * @fops: a pointer to a struct file_operations that should be used for
88  *        this file.
89  * @iops: a point to a struct of inode_operations that should be used for
90  *        this file/dir
91  *
92  * This is the basic "create a file/dir/symlink" function for
93  * securityfs.  It allows for a wide range of flexibility in creating
94  * a file, or a directory (if you want to create a directory, the
95  * securityfs_create_dir() function is recommended to be used
96  * instead).
97  *
98  * This function returns a pointer to a dentry if it succeeds.  This
99  * pointer must be passed to the securityfs_remove() function when the
100  * file is to be removed (no automatic cleanup happens if your module
101  * is unloaded, you are responsible here).  If an error occurs, the
102  * function will return the error value (via ERR_PTR).
103  *
104  * If securityfs is not enabled in the kernel, the value %-ENODEV is
105  * returned.
106  */
securityfs_create_dentry(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * fops,const struct inode_operations * iops)107 static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
108 					struct dentry *parent, void *data,
109 					const struct file_operations *fops,
110 					const struct inode_operations *iops)
111 {
112 	struct dentry *dentry;
113 	struct inode *dir, *inode;
114 	int error;
115 
116 	if (!(mode & S_IFMT))
117 		mode = (mode & S_IALLUGO) | S_IFREG;
118 
119 	pr_debug("securityfs: creating file '%s'\n",name);
120 
121 	error = simple_pin_fs(&fs_type, &mount, &mount_count);
122 	if (error)
123 		return ERR_PTR(error);
124 
125 	if (!parent)
126 		parent = mount->mnt_root;
127 
128 	dir = d_inode(parent);
129 
130 	inode_lock(dir);
131 	dentry = lookup_one_len(name, parent, strlen(name));
132 	if (IS_ERR(dentry))
133 		goto out;
134 
135 	if (d_really_is_positive(dentry)) {
136 		error = -EEXIST;
137 		goto out1;
138 	}
139 
140 	inode = new_inode(dir->i_sb);
141 	if (!inode) {
142 		error = -ENOMEM;
143 		goto out1;
144 	}
145 
146 	inode->i_ino = get_next_ino();
147 	inode->i_mode = mode;
148 	inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
149 	inode->i_private = data;
150 	if (S_ISDIR(mode)) {
151 		inode->i_op = &simple_dir_inode_operations;
152 		inode->i_fop = &simple_dir_operations;
153 		inc_nlink(inode);
154 		inc_nlink(dir);
155 	} else if (S_ISLNK(mode)) {
156 		inode->i_op = iops ? iops : &simple_symlink_inode_operations;
157 		inode->i_link = data;
158 	} else {
159 		inode->i_fop = fops;
160 	}
161 	d_instantiate(dentry, inode);
162 	dget(dentry);
163 	inode_unlock(dir);
164 	return dentry;
165 
166 out1:
167 	dput(dentry);
168 	dentry = ERR_PTR(error);
169 out:
170 	inode_unlock(dir);
171 	simple_release_fs(&mount, &mount_count);
172 	return dentry;
173 }
174 
175 /**
176  * securityfs_create_file - create a file in the securityfs filesystem
177  *
178  * @name: a pointer to a string containing the name of the file to create.
179  * @mode: the permission that the file should have
180  * @parent: a pointer to the parent dentry for this file.  This should be a
181  *          directory dentry if set.  If this parameter is %NULL, then the
182  *          file will be created in the root of the securityfs filesystem.
183  * @data: a pointer to something that the caller will want to get to later
184  *        on.  The inode.i_private pointer will point to this value on
185  *        the open() call.
186  * @fops: a pointer to a struct file_operations that should be used for
187  *        this file.
188  *
189  * This function creates a file in securityfs with the given @name.
190  *
191  * This function returns a pointer to a dentry if it succeeds.  This
192  * pointer must be passed to the securityfs_remove() function when the file is
193  * to be removed (no automatic cleanup happens if your module is unloaded,
194  * you are responsible here).  If an error occurs, the function will return
195  * the error value (via ERR_PTR).
196  *
197  * If securityfs is not enabled in the kernel, the value %-ENODEV is
198  * returned.
199  */
securityfs_create_file(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * fops)200 struct dentry *securityfs_create_file(const char *name, umode_t mode,
201 				      struct dentry *parent, void *data,
202 				      const struct file_operations *fops)
203 {
204 	return securityfs_create_dentry(name, mode, parent, data, fops, NULL);
205 }
206 EXPORT_SYMBOL_GPL(securityfs_create_file);
207 
208 /**
209  * securityfs_create_dir - create a directory in the securityfs filesystem
210  *
211  * @name: a pointer to a string containing the name of the directory to
212  *        create.
213  * @parent: a pointer to the parent dentry for this file.  This should be a
214  *          directory dentry if set.  If this parameter is %NULL, then the
215  *          directory will be created in the root of the securityfs filesystem.
216  *
217  * This function creates a directory in securityfs with the given @name.
218  *
219  * This function returns a pointer to a dentry if it succeeds.  This
220  * pointer must be passed to the securityfs_remove() function when the file is
221  * to be removed (no automatic cleanup happens if your module is unloaded,
222  * you are responsible here).  If an error occurs, the function will return
223  * the error value (via ERR_PTR).
224  *
225  * If securityfs is not enabled in the kernel, the value %-ENODEV is
226  * returned.
227  */
securityfs_create_dir(const char * name,struct dentry * parent)228 struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
229 {
230 	return securityfs_create_file(name, S_IFDIR | 0755, parent, NULL, NULL);
231 }
232 EXPORT_SYMBOL_GPL(securityfs_create_dir);
233 
234 /**
235  * securityfs_create_symlink - create a symlink in the securityfs filesystem
236  *
237  * @name: a pointer to a string containing the name of the symlink to
238  *        create.
239  * @parent: a pointer to the parent dentry for the symlink.  This should be a
240  *          directory dentry if set.  If this parameter is %NULL, then the
241  *          directory will be created in the root of the securityfs filesystem.
242  * @target: a pointer to a string containing the name of the symlink's target.
243  *          If this parameter is %NULL, then the @iops parameter needs to be
244  *          setup to handle .readlink and .get_link inode_operations.
245  * @iops: a pointer to the struct inode_operations to use for the symlink. If
246  *        this parameter is %NULL, then the default simple_symlink_inode
247  *        operations will be used.
248  *
249  * This function creates a symlink in securityfs with the given @name.
250  *
251  * This function returns a pointer to a dentry if it succeeds.  This
252  * pointer must be passed to the securityfs_remove() function when the file is
253  * to be removed (no automatic cleanup happens if your module is unloaded,
254  * you are responsible here).  If an error occurs, the function will return
255  * the error value (via ERR_PTR).
256  *
257  * If securityfs is not enabled in the kernel, the value %-ENODEV is
258  * returned.
259  */
securityfs_create_symlink(const char * name,struct dentry * parent,const char * target,const struct inode_operations * iops)260 struct dentry *securityfs_create_symlink(const char *name,
261 					 struct dentry *parent,
262 					 const char *target,
263 					 const struct inode_operations *iops)
264 {
265 	struct dentry *dent;
266 	char *link = NULL;
267 
268 	if (target) {
269 		link = kstrdup(target, GFP_KERNEL);
270 		if (!link)
271 			return ERR_PTR(-ENOMEM);
272 	}
273 	dent = securityfs_create_dentry(name, S_IFLNK | 0444, parent,
274 					link, NULL, iops);
275 	if (IS_ERR(dent))
276 		kfree(link);
277 
278 	return dent;
279 }
280 EXPORT_SYMBOL_GPL(securityfs_create_symlink);
281 
282 /**
283  * securityfs_remove - removes a file or directory from the securityfs filesystem
284  *
285  * @dentry: a pointer to a the dentry of the file or directory to be removed.
286  *
287  * This function removes a file or directory in securityfs that was previously
288  * created with a call to another securityfs function (like
289  * securityfs_create_file() or variants thereof.)
290  *
291  * This function is required to be called in order for the file to be
292  * removed. No automatic cleanup of files will happen when a module is
293  * removed; you are responsible here.
294  */
securityfs_remove(struct dentry * dentry)295 void securityfs_remove(struct dentry *dentry)
296 {
297 	struct inode *dir;
298 
299 	if (!dentry || IS_ERR(dentry))
300 		return;
301 
302 	dir = d_inode(dentry->d_parent);
303 	inode_lock(dir);
304 	if (simple_positive(dentry)) {
305 		if (d_is_dir(dentry))
306 			simple_rmdir(dir, dentry);
307 		else
308 			simple_unlink(dir, dentry);
309 		dput(dentry);
310 	}
311 	inode_unlock(dir);
312 	simple_release_fs(&mount, &mount_count);
313 }
314 EXPORT_SYMBOL_GPL(securityfs_remove);
315 
316 #ifdef CONFIG_SECURITY
317 static struct dentry *lsm_dentry;
lsm_read(struct file * filp,char __user * buf,size_t count,loff_t * ppos)318 static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
319 			loff_t *ppos)
320 {
321 	return simple_read_from_buffer(buf, count, ppos, lsm_names,
322 		strlen(lsm_names));
323 }
324 
325 static const struct file_operations lsm_ops = {
326 	.read = lsm_read,
327 	.llseek = generic_file_llseek,
328 };
329 #endif
330 
securityfs_init(void)331 static int __init securityfs_init(void)
332 {
333 	int retval;
334 
335 	retval = sysfs_create_mount_point(kernel_kobj, "security");
336 	if (retval)
337 		return retval;
338 
339 	retval = register_filesystem(&fs_type);
340 	if (retval) {
341 		sysfs_remove_mount_point(kernel_kobj, "security");
342 		return retval;
343 	}
344 #ifdef CONFIG_SECURITY
345 	lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
346 						&lsm_ops);
347 #endif
348 	return 0;
349 }
350 core_initcall(securityfs_init);
351