1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * fs/anon_inodes.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 *
7 * Thanks to Arnd Bergmann for code review and suggestions.
8 * More changes for Thomas Gleixner suggestions.
9 *
10 */
11
12 #include <linux/cred.h>
13 #include <linux/file.h>
14 #include <linux/poll.h>
15 #include <linux/sched.h>
16 #include <linux/init.h>
17 #include <linux/fs.h>
18 #include <linux/mount.h>
19 #include <linux/module.h>
20 #include <linux/kernel.h>
21 #include <linux/magic.h>
22 #include <linux/anon_inodes.h>
23 #include <linux/pseudo_fs.h>
24
25 #include <linux/uaccess.h>
26
27 static struct vfsmount *anon_inode_mnt __read_mostly;
28 static struct inode *anon_inode_inode;
29
30 /*
31 * anon_inodefs_dname() is called from d_path().
32 */
anon_inodefs_dname(struct dentry * dentry,char * buffer,int buflen)33 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
34 {
35 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
36 dentry->d_name.name);
37 }
38
39 static const struct dentry_operations anon_inodefs_dentry_operations = {
40 .d_dname = anon_inodefs_dname,
41 };
42
anon_inodefs_init_fs_context(struct fs_context * fc)43 static int anon_inodefs_init_fs_context(struct fs_context *fc)
44 {
45 struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
46 if (!ctx)
47 return -ENOMEM;
48 ctx->dops = &anon_inodefs_dentry_operations;
49 return 0;
50 }
51
52 static struct file_system_type anon_inode_fs_type = {
53 .name = "anon_inodefs",
54 .init_fs_context = anon_inodefs_init_fs_context,
55 .kill_sb = kill_anon_super,
56 };
57
anon_inode_make_secure_inode(const char * name,const struct inode * context_inode)58 static struct inode *anon_inode_make_secure_inode(
59 const char *name,
60 const struct inode *context_inode)
61 {
62 struct inode *inode;
63 const struct qstr qname = QSTR_INIT(name, strlen(name));
64 int error;
65
66 inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
67 if (IS_ERR(inode))
68 return inode;
69 inode->i_flags &= ~S_PRIVATE;
70 error = security_inode_init_security_anon(inode, &qname, context_inode);
71 if (error) {
72 iput(inode);
73 return ERR_PTR(error);
74 }
75 return inode;
76 }
77
__anon_inode_getfile(const char * name,const struct file_operations * fops,void * priv,int flags,const struct inode * context_inode,bool secure)78 static struct file *__anon_inode_getfile(const char *name,
79 const struct file_operations *fops,
80 void *priv, int flags,
81 const struct inode *context_inode,
82 bool secure)
83 {
84 struct inode *inode;
85 struct file *file;
86
87 if (fops->owner && !try_module_get(fops->owner))
88 return ERR_PTR(-ENOENT);
89
90 if (secure) {
91 inode = anon_inode_make_secure_inode(name, context_inode);
92 if (IS_ERR(inode)) {
93 file = ERR_CAST(inode);
94 goto err;
95 }
96 } else {
97 inode = anon_inode_inode;
98 if (IS_ERR(inode)) {
99 file = ERR_PTR(-ENODEV);
100 goto err;
101 }
102 /*
103 * We know the anon_inode inode count is always
104 * greater than zero, so ihold() is safe.
105 */
106 ihold(inode);
107 }
108
109 file = alloc_file_pseudo(inode, anon_inode_mnt, name,
110 flags & (O_ACCMODE | O_NONBLOCK), fops);
111 if (IS_ERR(file))
112 goto err_iput;
113
114 file->f_mapping = inode->i_mapping;
115
116 file->private_data = priv;
117
118 return file;
119
120 err_iput:
121 iput(inode);
122 err:
123 module_put(fops->owner);
124 return file;
125 }
126
127 /**
128 * anon_inode_getfile - creates a new file instance by hooking it up to an
129 * anonymous inode, and a dentry that describe the "class"
130 * of the file
131 *
132 * @name: [in] name of the "class" of the new file
133 * @fops: [in] file operations for the new file
134 * @priv: [in] private data for the new file (will be file's private_data)
135 * @flags: [in] flags
136 *
137 * Creates a new file by hooking it on a single inode. This is useful for files
138 * that do not need to have a full-fledged inode in order to operate correctly.
139 * All the files created with anon_inode_getfile() will share a single inode,
140 * hence saving memory and avoiding code duplication for the file/inode/dentry
141 * setup. Returns the newly created file* or an error pointer.
142 */
anon_inode_getfile(const char * name,const struct file_operations * fops,void * priv,int flags)143 struct file *anon_inode_getfile(const char *name,
144 const struct file_operations *fops,
145 void *priv, int flags)
146 {
147 return __anon_inode_getfile(name, fops, priv, flags, NULL, false);
148 }
149 EXPORT_SYMBOL_GPL(anon_inode_getfile);
150
__anon_inode_getfd(const char * name,const struct file_operations * fops,void * priv,int flags,const struct inode * context_inode,bool secure)151 static int __anon_inode_getfd(const char *name,
152 const struct file_operations *fops,
153 void *priv, int flags,
154 const struct inode *context_inode,
155 bool secure)
156 {
157 int error, fd;
158 struct file *file;
159
160 error = get_unused_fd_flags(flags);
161 if (error < 0)
162 return error;
163 fd = error;
164
165 file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
166 secure);
167 if (IS_ERR(file)) {
168 error = PTR_ERR(file);
169 goto err_put_unused_fd;
170 }
171 fd_install(fd, file);
172
173 return fd;
174
175 err_put_unused_fd:
176 put_unused_fd(fd);
177 return error;
178 }
179
180 /**
181 * anon_inode_getfd - creates a new file instance by hooking it up to
182 * an anonymous inode and a dentry that describe
183 * the "class" of the file
184 *
185 * @name: [in] name of the "class" of the new file
186 * @fops: [in] file operations for the new file
187 * @priv: [in] private data for the new file (will be file's private_data)
188 * @flags: [in] flags
189 *
190 * Creates a new file by hooking it on a single inode. This is
191 * useful for files that do not need to have a full-fledged inode in
192 * order to operate correctly. All the files created with
193 * anon_inode_getfd() will use the same singleton inode, reducing
194 * memory use and avoiding code duplication for the file/inode/dentry
195 * setup. Returns a newly created file descriptor or an error code.
196 */
anon_inode_getfd(const char * name,const struct file_operations * fops,void * priv,int flags)197 int anon_inode_getfd(const char *name, const struct file_operations *fops,
198 void *priv, int flags)
199 {
200 return __anon_inode_getfd(name, fops, priv, flags, NULL, false);
201 }
202 EXPORT_SYMBOL_GPL(anon_inode_getfd);
203
204 /**
205 * anon_inode_getfd_secure - Like anon_inode_getfd(), but creates a new
206 * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls
207 * the inode_init_security_anon() LSM hook. This allows the inode to have its
208 * own security context and for a LSM to reject creation of the inode.
209 *
210 * @name: [in] name of the "class" of the new file
211 * @fops: [in] file operations for the new file
212 * @priv: [in] private data for the new file (will be file's private_data)
213 * @flags: [in] flags
214 * @context_inode:
215 * [in] the logical relationship with the new inode (optional)
216 *
217 * The LSM may use @context_inode in inode_init_security_anon(), but a
218 * reference to it is not held.
219 */
anon_inode_getfd_secure(const char * name,const struct file_operations * fops,void * priv,int flags,const struct inode * context_inode)220 int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
221 void *priv, int flags,
222 const struct inode *context_inode)
223 {
224 return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
225 }
226 EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);
227
anon_inode_init(void)228 static int __init anon_inode_init(void)
229 {
230 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
231 if (IS_ERR(anon_inode_mnt))
232 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
233
234 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
235 if (IS_ERR(anon_inode_inode))
236 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
237
238 return 0;
239 }
240
241 fs_initcall(anon_inode_init);
242
243