fs/filesystems.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/filesystems.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *
   7  *  table of configured filesystems
   8  */
   9
  10 #include <linux/syscalls.h>
  11 #include <linux/fs.h>
  12 #include <linux/proc_fs.h>
  13 #include <linux/seq_file.h>
  14 #include <linux/kmod.h>
  15 #include <linux/init.h>
  16 #include <linux/module.h>
  17 #include <linux/slab.h>
  18 #include <linux/uaccess.h>
  19 #include <linux/fs_parser.h>
  20
  21 /*
  22  * Handling of filesystem drivers list.
  23  * Rules:
  24  *      Inclusion to/removals from/scanning of list are protected by spinlock.
  25  *      During the unload module must call unregister_filesystem().
  26  *      We can access the fields of list element if:
  27  *              1) spinlock is held or
  28  *              2) we hold the reference to the module.
  29  *      The latter can be guaranteed by call of try_module_get(); if it
  30  *      returned 0 we must skip the element, otherwise we got the reference.
  31  *      Once the reference is obtained we can drop the spinlock.
  32  */
  33
  34 static struct file_system_type *file_systems;
  35 static DEFINE_RWLOCK(file_systems_lock);
  36
  37 /* WARNING: This can be used only if we _already_ own a reference */
  38 struct file_system_type *get_filesystem(struct file_system_type *fs)
  39 {
  40         __module_get(fs->owner);
  41         return fs;
  42 }
  43
  44 void put_filesystem(struct file_system_type *fs)
  45 {
  46         module_put(fs->owner);
  47 }
  48
  49 static struct file_system_type **find_filesystem(const char *name, unsigned len)
  50 {
  51         struct file_system_type **p;
  52         for (p = &file_systems; *p; p = &(*p)->next)
  53                 if (strncmp((*p)->name, name, len) == 0 &&
  54                     !(*p)->name[len])
  55                         break;
  56         return p;
  57 }
  58
  59 /**
  60  *      register_filesystem - register a new filesystem
  61  *      @fs: the file system structure
  62  *
  63  *      Adds the file system passed to the list of file systems the kernel
  64  *      is aware of for mount and other syscalls. Returns 0 on success,
  65  *      or a negative errno code on an error.
  66  *
  67  *      The &struct file_system_type that is passed is linked into the kernel
  68  *      structures and must not be freed until the file system has been
  69  *      unregistered.
  70  */
  71
  72 int register_filesystem(struct file_system_type * fs)
  73 {
  74         int res = 0;
  75         struct file_system_type ** p;
  76
  77         if (fs->parameters &&
  78             !fs_validate_description(fs->name, fs->parameters))
  79                 return -EINVAL;
  80
  81         BUG_ON(strchr(fs->name, '.'));
  82         if (fs->next)
  83                 return -EBUSY;
  84         write_lock(&file_systems_lock);
  85         p = find_filesystem(fs->name, strlen(fs->name));
  86         if (*p)
  87                 res = -EBUSY;
  88         else
  89                 *p = fs;
  90         write_unlock(&file_systems_lock);
  91         return res;
  92 }
  93
  94 EXPORT_SYMBOL(register_filesystem);
  95
  96 /**
  97  *      unregister_filesystem - unregister a file system
  98  *      @fs: filesystem to unregister
  99  *
 100  *      Remove a file system that was previously successfully registered
 101  *      with the kernel. An error is returned if the file system is not found.
 102  *      Zero is returned on a success.
 103  *
 104  *      Once this function has returned the &struct file_system_type structure
 105  *      may be freed or reused.
 106  */
 107
 108 int unregister_filesystem(struct file_system_type * fs)
 109 {
 110         struct file_system_type ** tmp;
 111
 112         write_lock(&file_systems_lock);
 113         tmp = &file_systems;
 114         while (*tmp) {
 115                 if (fs == *tmp) {
 116                         *tmp = fs->next;
 117                         fs->next = NULL;
 118                         write_unlock(&file_systems_lock);
 119                         synchronize_rcu();
 120                         return 0;
 121                 }
 122                 tmp = &(*tmp)->next;
 123         }
 124         write_unlock(&file_systems_lock);
 125
 126         return -EINVAL;
 127 }
 128
 129 EXPORT_SYMBOL(unregister_filesystem);
 130
 131 #ifdef CONFIG_SYSFS_SYSCALL
 132 static int fs_index(const char __user * __name)
 133 {
 134         struct file_system_type * tmp;
 135         struct filename *name;
 136         int err, index;
 137
 138         name = getname(__name);
 139         err = PTR_ERR(name);
 140         if (IS_ERR(name))
 141                 return err;
 142
 143         err = -EINVAL;
 144         read_lock(&file_systems_lock);
 145         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 146                 if (strcmp(tmp->name, name->name) == 0) {
 147                         err = index;
 148                         break;
 149                 }
 150         }
 151         read_unlock(&file_systems_lock);
 152         putname(name);
 153         return err;
 154 }
 155
 156 static int fs_name(unsigned int index, char __user * buf)
 157 {
 158         struct file_system_type * tmp;
 159         int len, res;
 160
 161         read_lock(&file_systems_lock);
 162         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 163                 if (index <= 0 && try_module_get(tmp->owner))
 164                         break;
 165         read_unlock(&file_systems_lock);
 166         if (!tmp)
 167                 return -EINVAL;
 168
 169         /* OK, we got the reference, so we can safely block */
 170         len = strlen(tmp->name) + 1;
 171         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 172         put_filesystem(tmp);
 173         return res;
 174 }
 175
 176 static int fs_maxindex(void)
 177 {
 178         struct file_system_type * tmp;
 179         int index;
 180
 181         read_lock(&file_systems_lock);
 182         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 183                 ;
 184         read_unlock(&file_systems_lock);
 185         return index;
 186 }
 187
 188 /*
 189  * Whee.. Weird sysv syscall.
 190  */
 191 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
 192 {
 193         int retval = -EINVAL;
 194
 195         switch (option) {
 196                 case 1:
 197                         retval = fs_index((const char __user *) arg1);
 198                         break;
 199
 200                 case 2:
 201                         retval = fs_name(arg1, (char __user *) arg2);
 202                         break;
 203
 204                 case 3:
 205                         retval = fs_maxindex();
 206                         break;
 207         }
 208         return retval;
 209 }
 210 #endif
 211
 212 int __init list_bdev_fs_names(char *buf, size_t size)
 213 {
 214         struct file_system_type *p;
 215         size_t len;
 216         int count = 0;
 217
 218         read_lock(&file_systems_lock);
 219         for (p = file_systems; p; p = p->next) {
 220                 if (!(p->fs_flags & FS_REQUIRES_DEV))
 221                         continue;
 222                 len = strlen(p->name) + 1;
 223                 if (len > size) {
 224                         pr_warn("%s: truncating file system list\n", __func__);
 225                         break;
 226                 }
 227                 memcpy(buf, p->name, len);
 228                 buf += len;
 229                 size -= len;
 230                 count++;
 231         }
 232         read_unlock(&file_systems_lock);
 233         return count;
 234 }
 235
 236 #ifdef CONFIG_PROC_FS
 237 static int filesystems_proc_show(struct seq_file *m, void *v)
 238 {
 239         struct file_system_type * tmp;
 240
 241         read_lock(&file_systems_lock);
 242         tmp = file_systems;
 243         while (tmp) {
 244                 seq_printf(m, "%s\t%s\n",
 245                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 246                         tmp->name);
 247                 tmp = tmp->next;
 248         }
 249         read_unlock(&file_systems_lock);
 250         return 0;
 251 }
 252
 253 static int __init proc_filesystems_init(void)
 254 {
 255         proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
 256         return 0;
 257 }
 258 module_init(proc_filesystems_init);
 259 #endif
 260
 261 static struct file_system_type *__get_fs_type(const char *name, int len)
 262 {
 263         struct file_system_type *fs;
 264
 265         read_lock(&file_systems_lock);
 266         fs = *(find_filesystem(name, len));
 267         if (fs && !try_module_get(fs->owner))
 268                 fs = NULL;
 269         read_unlock(&file_systems_lock);
 270         return fs;
 271 }
 272
 273 struct file_system_type *get_fs_type(const char *name)
 274 {
 275         struct file_system_type *fs;
 276         const char *dot = strchr(name, '.');
 277         int len = dot ? dot - name : strlen(name);
 278
 279         fs = __get_fs_type(name, len);
 280         if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
 281                 fs = __get_fs_type(name, len);
 282                 if (!fs)
 283                         pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
 284                                      len, name);
 285         }
 286
 287         if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 288                 put_filesystem(fs);
 289                 fs = NULL;
 290         }
 291         return fs;
 292 }
 293
 294 EXPORT_SYMBOL(get_fs_type);