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
  20 /*
  21  * Handling of filesystem drivers list.
  22  * Rules:
  23  *      Inclusion to/removals from/scanning of list are protected by spinlock.
  24  *      During the unload module must call unregister_filesystem().
  25  *      We can access the fields of list element if:
  26  *              1) spinlock is held or
  27  *              2) we hold the reference to the module.
  28  *      The latter can be guaranteed by call of try_module_get(); if it
  29  *      returned 0 we must skip the element, otherwise we got the reference.
  30  *      Once the reference is obtained we can drop the spinlock.
  31  */
  32
  33 static struct file_system_type *file_systems;
  34 static DEFINE_RWLOCK(file_systems_lock);
  35
  36 /* WARNING: This can be used only if we _already_ own a reference */
  37 struct file_system_type *get_filesystem(struct file_system_type *fs)
  38 {
  39         __module_get(fs->owner);
  40         return fs;
  41 }
  42
  43 void put_filesystem(struct file_system_type *fs)
  44 {
  45         module_put(fs->owner);
  46 }
  47
  48 static struct file_system_type **find_filesystem(const char *name, unsigned len)
  49 {
  50         struct file_system_type **p;
  51         for (p = &file_systems; *p; p = &(*p)->next)
  52                 if (strncmp((*p)->name, name, len) == 0 &&
  53                     !(*p)->name[len])
  54                         break;
  55         return p;
  56 }
  57
  58 /**
  59  *      register_filesystem - register a new filesystem
  60  *      @fs: the file system structure
  61  *
  62  *      Adds the file system passed to the list of file systems the kernel
  63  *      is aware of for mount and other syscalls. Returns 0 on success,
  64  *      or a negative errno code on an error.
  65  *
  66  *      The &struct file_system_type that is passed is linked into the kernel
  67  *      structures and must not be freed until the file system has been
  68  *      unregistered.
  69  */
  70
  71 int register_filesystem(struct file_system_type * fs)
  72 {
  73         int res = 0;
  74         struct file_system_type ** p;
  75
  76         BUG_ON(strchr(fs->name, '.'));
  77         if (fs->next)
  78                 return -EBUSY;
  79         write_lock(&file_systems_lock);
  80         p = find_filesystem(fs->name, strlen(fs->name));
  81         if (*p)
  82                 res = -EBUSY;
  83         else
  84                 *p = fs;
  85         write_unlock(&file_systems_lock);
  86         return res;
  87 }
  88
  89 EXPORT_SYMBOL(register_filesystem);
  90
  91 /**
  92  *      unregister_filesystem - unregister a file system
  93  *      @fs: filesystem to unregister
  94  *
  95  *      Remove a file system that was previously successfully registered
  96  *      with the kernel. An error is returned if the file system is not found.
  97  *      Zero is returned on a success.
  98  *
  99  *      Once this function has returned the &struct file_system_type structure
 100  *      may be freed or reused.
 101  */
 102
 103 int unregister_filesystem(struct file_system_type * fs)
 104 {
 105         struct file_system_type ** tmp;
 106
 107         write_lock(&file_systems_lock);
 108         tmp = &file_systems;
 109         while (*tmp) {
 110                 if (fs == *tmp) {
 111                         *tmp = fs->next;
 112                         fs->next = NULL;
 113                         write_unlock(&file_systems_lock);
 114                         synchronize_rcu();
 115                         return 0;
 116                 }
 117                 tmp = &(*tmp)->next;
 118         }
 119         write_unlock(&file_systems_lock);
 120
 121         return -EINVAL;
 122 }
 123
 124 EXPORT_SYMBOL(unregister_filesystem);
 125
 126 #ifdef CONFIG_SYSFS_SYSCALL
 127 static int fs_index(const char __user * __name)
 128 {
 129         struct file_system_type * tmp;
 130         struct filename *name;
 131         int err, index;
 132
 133         name = getname(__name);
 134         err = PTR_ERR(name);
 135         if (IS_ERR(name))
 136                 return err;
 137
 138         err = -EINVAL;
 139         read_lock(&file_systems_lock);
 140         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 141                 if (strcmp(tmp->name, name->name) == 0) {
 142                         err = index;
 143                         break;
 144                 }
 145         }
 146         read_unlock(&file_systems_lock);
 147         putname(name);
 148         return err;
 149 }
 150
 151 static int fs_name(unsigned int index, char __user * buf)
 152 {
 153         struct file_system_type * tmp;
 154         int len, res;
 155
 156         read_lock(&file_systems_lock);
 157         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 158                 if (index <= 0 && try_module_get(tmp->owner))
 159                         break;
 160         read_unlock(&file_systems_lock);
 161         if (!tmp)
 162                 return -EINVAL;
 163
 164         /* OK, we got the reference, so we can safely block */
 165         len = strlen(tmp->name) + 1;
 166         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 167         put_filesystem(tmp);
 168         return res;
 169 }
 170
 171 static int fs_maxindex(void)
 172 {
 173         struct file_system_type * tmp;
 174         int index;
 175
 176         read_lock(&file_systems_lock);
 177         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 178                 ;
 179         read_unlock(&file_systems_lock);
 180         return index;
 181 }
 182
 183 /*
 184  * Whee.. Weird sysv syscall.
 185  */
 186 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
 187 {
 188         int retval = -EINVAL;
 189
 190         switch (option) {
 191                 case 1:
 192                         retval = fs_index((const char __user *) arg1);
 193                         break;
 194
 195                 case 2:
 196                         retval = fs_name(arg1, (char __user *) arg2);
 197                         break;
 198
 199                 case 3:
 200                         retval = fs_maxindex();
 201                         break;
 202         }
 203         return retval;
 204 }
 205 #endif
 206
 207 int __init get_filesystem_list(char *buf)
 208 {
 209         int len = 0;
 210         struct file_system_type * tmp;
 211
 212         read_lock(&file_systems_lock);
 213         tmp = file_systems;
 214         while (tmp && len < PAGE_SIZE - 80) {
 215                 len += sprintf(buf+len, "%s\t%s\n",
 216                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 217                         tmp->name);
 218                 tmp = tmp->next;
 219         }
 220         read_unlock(&file_systems_lock);
 221         return len;
 222 }
 223
 224 #ifdef CONFIG_PROC_FS
 225 static int filesystems_proc_show(struct seq_file *m, void *v)
 226 {
 227         struct file_system_type * tmp;
 228
 229         read_lock(&file_systems_lock);
 230         tmp = file_systems;
 231         while (tmp) {
 232                 seq_printf(m, "%s\t%s\n",
 233                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 234                         tmp->name);
 235                 tmp = tmp->next;
 236         }
 237         read_unlock(&file_systems_lock);
 238         return 0;
 239 }
 240
 241 static int filesystems_proc_open(struct inode *inode, struct file *file)
 242 {
 243         return single_open(file, filesystems_proc_show, NULL);
 244 }
 245
 246 static const struct file_operations filesystems_proc_fops = {
 247         .open           = filesystems_proc_open,
 248         .read           = seq_read,
 249         .llseek         = seq_lseek,
 250         .release        = single_release,
 251 };
 252
 253 static int __init proc_filesystems_init(void)
 254 {
 255         proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 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);