fs/anon_inodes.c

   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  */
  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
  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
  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
  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  */
 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
 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  */
 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  */
 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
 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