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Linux/security/inode.c

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  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 
 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 
 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 
 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 
 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  */
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  */
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  */
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  */
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  */
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;
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 
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 

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