1 /* 2 * linux/fs/file_table.c 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 * Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu) 6 */ 7 8 #include <linux/string.h> 9 #include <linux/slab.h> 10 #include <linux/file.h> 11 #include <linux/fdtable.h> 12 #include <linux/init.h> 13 #include <linux/module.h> 14 #include <linux/fs.h> 15 #include <linux/security.h> 16 #include <linux/ima.h> 17 #include <linux/eventpoll.h> 18 #include <linux/rcupdate.h> 19 #include <linux/mount.h> 20 #include <linux/capability.h> 21 #include <linux/cdev.h> 22 #include <linux/fsnotify.h> 23 #include <linux/sysctl.h> 24 #include <linux/percpu_counter.h> 25 26 #include <asm/atomic.h> 27 28 /* sysctl tunables... */ 29 struct files_stat_struct files_stat = { 30 .max_files = NR_FILE 31 }; 32 33 /* public. Not pretty! */ 34 __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock); 35 36 /* SLAB cache for file structures */ 37 static struct kmem_cache *filp_cachep __read_mostly; 38 39 static struct percpu_counter nr_files __cacheline_aligned_in_smp; 40 41 static inline void file_free_rcu(struct rcu_head *head) 42 { 43 struct file *f = container_of(head, struct file, f_u.fu_rcuhead); 44 45 put_cred(f->f_cred); 46 kmem_cache_free(filp_cachep, f); 47 } 48 49 static inline void file_free(struct file *f) 50 { 51 percpu_counter_dec(&nr_files); 52 file_check_state(f); 53 call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); 54 } 55 56 /* 57 * Return the total number of open files in the system 58 */ 59 static int get_nr_files(void) 60 { 61 return percpu_counter_read_positive(&nr_files); 62 } 63 64 /* 65 * Return the maximum number of open files in the system 66 */ 67 int get_max_files(void) 68 { 69 return files_stat.max_files; 70 } 71 EXPORT_SYMBOL_GPL(get_max_files); 72 73 /* 74 * Handle nr_files sysctl 75 */ 76 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) 77 int proc_nr_files(ctl_table *table, int write, struct file *filp, 78 void __user *buffer, size_t *lenp, loff_t *ppos) 79 { 80 files_stat.nr_files = get_nr_files(); 81 return proc_dointvec(table, write, filp, buffer, lenp, ppos); 82 } 83 #else 84 int proc_nr_files(ctl_table *table, int write, struct file *filp, 85 void __user *buffer, size_t *lenp, loff_t *ppos) 86 { 87 return -ENOSYS; 88 } 89 #endif 90 91 /* Find an unused file structure and return a pointer to it. 92 * Returns NULL, if there are no more free file structures or 93 * we run out of memory. 94 * 95 * Be very careful using this. You are responsible for 96 * getting write access to any mount that you might assign 97 * to this filp, if it is opened for write. If this is not 98 * done, you will imbalance int the mount's writer count 99 * and a warning at __fput() time. 100 */ 101 struct file *get_empty_filp(void) 102 { 103 const struct cred *cred = current_cred(); 104 static int old_max; 105 struct file * f; 106 107 /* 108 * Privileged users can go above max_files 109 */ 110 if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { 111 /* 112 * percpu_counters are inaccurate. Do an expensive check before 113 * we go and fail. 114 */ 115 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files) 116 goto over; 117 } 118 119 f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); 120 if (f == NULL) 121 goto fail; 122 123 percpu_counter_inc(&nr_files); 124 if (security_file_alloc(f)) 125 goto fail_sec; 126 127 INIT_LIST_HEAD(&f->f_u.fu_list); 128 atomic_long_set(&f->f_count, 1); 129 rwlock_init(&f->f_owner.lock); 130 f->f_cred = get_cred(cred); 131 spin_lock_init(&f->f_lock); 132 eventpoll_init_file(f); 133 /* f->f_version: 0 */ 134 return f; 135 136 over: 137 /* Ran out of filps - report that */ 138 if (get_nr_files() > old_max) { 139 printk(KERN_INFO "VFS: file-max limit %d reached\n", 140 get_max_files()); 141 old_max = get_nr_files(); 142 } 143 goto fail; 144 145 fail_sec: 146 file_free(f); 147 fail: 148 return NULL; 149 } 150 151 EXPORT_SYMBOL(get_empty_filp); 152 153 /** 154 * alloc_file - allocate and initialize a 'struct file' 155 * @mnt: the vfsmount on which the file will reside 156 * @dentry: the dentry representing the new file 157 * @mode: the mode with which the new file will be opened 158 * @fop: the 'struct file_operations' for the new file 159 * 160 * Use this instead of get_empty_filp() to get a new 161 * 'struct file'. Do so because of the same initialization 162 * pitfalls reasons listed for init_file(). This is a 163 * preferred interface to using init_file(). 164 * 165 * If all the callers of init_file() are eliminated, its 166 * code should be moved into this function. 167 */ 168 struct file *alloc_file(struct vfsmount *mnt, struct dentry *dentry, 169 fmode_t mode, const struct file_operations *fop) 170 { 171 struct file *file; 172 173 file = get_empty_filp(); 174 if (!file) 175 return NULL; 176 177 init_file(file, mnt, dentry, mode, fop); 178 return file; 179 } 180 EXPORT_SYMBOL(alloc_file); 181 182 /** 183 * init_file - initialize a 'struct file' 184 * @file: the already allocated 'struct file' to initialized 185 * @mnt: the vfsmount on which the file resides 186 * @dentry: the dentry representing this file 187 * @mode: the mode the file is opened with 188 * @fop: the 'struct file_operations' for this file 189 * 190 * Use this instead of setting the members directly. Doing so 191 * avoids making mistakes like forgetting the mntget() or 192 * forgetting to take a write on the mnt. 193 * 194 * Note: This is a crappy interface. It is here to make 195 * merging with the existing users of get_empty_filp() 196 * who have complex failure logic easier. All users 197 * of this should be moving to alloc_file(). 198 */ 199 int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry, 200 fmode_t mode, const struct file_operations *fop) 201 { 202 int error = 0; 203 file->f_path.dentry = dentry; 204 file->f_path.mnt = mntget(mnt); 205 file->f_mapping = dentry->d_inode->i_mapping; 206 file->f_mode = mode; 207 file->f_op = fop; 208 209 /* 210 * These mounts don't really matter in practice 211 * for r/o bind mounts. They aren't userspace- 212 * visible. We do this for consistency, and so 213 * that we can do debugging checks at __fput() 214 */ 215 if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) { 216 file_take_write(file); 217 error = mnt_want_write(mnt); 218 WARN_ON(error); 219 } 220 return error; 221 } 222 EXPORT_SYMBOL(init_file); 223 224 void fput(struct file *file) 225 { 226 if (atomic_long_dec_and_test(&file->f_count)) 227 __fput(file); 228 } 229 230 EXPORT_SYMBOL(fput); 231 232 /** 233 * drop_file_write_access - give up ability to write to a file 234 * @file: the file to which we will stop writing 235 * 236 * This is a central place which will give up the ability 237 * to write to @file, along with access to write through 238 * its vfsmount. 239 */ 240 void drop_file_write_access(struct file *file) 241 { 242 struct vfsmount *mnt = file->f_path.mnt; 243 struct dentry *dentry = file->f_path.dentry; 244 struct inode *inode = dentry->d_inode; 245 246 put_write_access(inode); 247 248 if (special_file(inode->i_mode)) 249 return; 250 if (file_check_writeable(file) != 0) 251 return; 252 mnt_drop_write(mnt); 253 file_release_write(file); 254 } 255 EXPORT_SYMBOL_GPL(drop_file_write_access); 256 257 /* __fput is called from task context when aio completion releases the last 258 * last use of a struct file *. Do not use otherwise. 259 */ 260 void __fput(struct file *file) 261 { 262 struct dentry *dentry = file->f_path.dentry; 263 struct vfsmount *mnt = file->f_path.mnt; 264 struct inode *inode = dentry->d_inode; 265 266 might_sleep(); 267 268 fsnotify_close(file); 269 /* 270 * The function eventpoll_release() should be the first called 271 * in the file cleanup chain. 272 */ 273 eventpoll_release(file); 274 locks_remove_flock(file); 275 276 if (unlikely(file->f_flags & FASYNC)) { 277 if (file->f_op && file->f_op->fasync) 278 file->f_op->fasync(-1, file, 0); 279 } 280 if (file->f_op && file->f_op->release) 281 file->f_op->release(inode, file); 282 security_file_free(file); 283 ima_file_free(file); 284 if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL)) 285 cdev_put(inode->i_cdev); 286 fops_put(file->f_op); 287 put_pid(file->f_owner.pid); 288 file_kill(file); 289 if (file->f_mode & FMODE_WRITE) 290 drop_file_write_access(file); 291 file->f_path.dentry = NULL; 292 file->f_path.mnt = NULL; 293 file_free(file); 294 dput(dentry); 295 mntput(mnt); 296 } 297 298 struct file *fget(unsigned int fd) 299 { 300 struct file *file; 301 struct files_struct *files = current->files; 302 303 rcu_read_lock(); 304 file = fcheck_files(files, fd); 305 if (file) { 306 if (!atomic_long_inc_not_zero(&file->f_count)) { 307 /* File object ref couldn't be taken */ 308 rcu_read_unlock(); 309 return NULL; 310 } 311 } 312 rcu_read_unlock(); 313 314 return file; 315 } 316 317 EXPORT_SYMBOL(fget); 318 319 /* 320 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 321 * You can use this only if it is guranteed that the current task already 322 * holds a refcnt to that file. That check has to be done at fget() only 323 * and a flag is returned to be passed to the corresponding fput_light(). 324 * There must not be a cloning between an fget_light/fput_light pair. 325 */ 326 struct file *fget_light(unsigned int fd, int *fput_needed) 327 { 328 struct file *file; 329 struct files_struct *files = current->files; 330 331 *fput_needed = 0; 332 if (likely((atomic_read(&files->count) == 1))) { 333 file = fcheck_files(files, fd); 334 } else { 335 rcu_read_lock(); 336 file = fcheck_files(files, fd); 337 if (file) { 338 if (atomic_long_inc_not_zero(&file->f_count)) 339 *fput_needed = 1; 340 else 341 /* Didn't get the reference, someone's freed */ 342 file = NULL; 343 } 344 rcu_read_unlock(); 345 } 346 347 return file; 348 } 349 350 351 void put_filp(struct file *file) 352 { 353 if (atomic_long_dec_and_test(&file->f_count)) { 354 security_file_free(file); 355 file_kill(file); 356 file_free(file); 357 } 358 } 359 360 void file_move(struct file *file, struct list_head *list) 361 { 362 if (!list) 363 return; 364 file_list_lock(); 365 list_move(&file->f_u.fu_list, list); 366 file_list_unlock(); 367 } 368 369 void file_kill(struct file *file) 370 { 371 if (!list_empty(&file->f_u.fu_list)) { 372 file_list_lock(); 373 list_del_init(&file->f_u.fu_list); 374 file_list_unlock(); 375 } 376 } 377 378 int fs_may_remount_ro(struct super_block *sb) 379 { 380 struct file *file; 381 382 /* Check that no files are currently opened for writing. */ 383 file_list_lock(); 384 list_for_each_entry(file, &sb->s_files, f_u.fu_list) { 385 struct inode *inode = file->f_path.dentry->d_inode; 386 387 /* File with pending delete? */ 388 if (inode->i_nlink == 0) 389 goto too_bad; 390 391 /* Writeable file? */ 392 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 393 goto too_bad; 394 } 395 file_list_unlock(); 396 return 1; /* Tis' cool bro. */ 397 too_bad: 398 file_list_unlock(); 399 return 0; 400 } 401 402 void __init files_init(unsigned long mempages) 403 { 404 int n; 405 406 filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, 407 SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); 408 409 /* 410 * One file with associated inode and dcache is very roughly 1K. 411 * Per default don't use more than 10% of our memory for files. 412 */ 413 414 n = (mempages * (PAGE_SIZE / 1024)) / 10; 415 files_stat.max_files = n; 416 if (files_stat.max_files < NR_FILE) 417 files_stat.max_files = NR_FILE; 418 files_defer_init(); 419 percpu_counter_init(&nr_files, 0); 420 } 421