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 struct path; 173 174 file = get_empty_filp(); 175 if (!file) 176 return NULL; 177 178 init_file(file, mnt, dentry, mode, fop); 179 return file; 180 } 181 EXPORT_SYMBOL(alloc_file); 182 183 /** 184 * init_file - initialize a 'struct file' 185 * @file: the already allocated 'struct file' to initialized 186 * @mnt: the vfsmount on which the file resides 187 * @dentry: the dentry representing this file 188 * @mode: the mode the file is opened with 189 * @fop: the 'struct file_operations' for this file 190 * 191 * Use this instead of setting the members directly. Doing so 192 * avoids making mistakes like forgetting the mntget() or 193 * forgetting to take a write on the mnt. 194 * 195 * Note: This is a crappy interface. It is here to make 196 * merging with the existing users of get_empty_filp() 197 * who have complex failure logic easier. All users 198 * of this should be moving to alloc_file(). 199 */ 200 int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry, 201 fmode_t mode, const struct file_operations *fop) 202 { 203 int error = 0; 204 file->f_path.dentry = dentry; 205 file->f_path.mnt = mntget(mnt); 206 file->f_mapping = dentry->d_inode->i_mapping; 207 file->f_mode = mode; 208 file->f_op = fop; 209 210 /* 211 * These mounts don't really matter in practice 212 * for r/o bind mounts. They aren't userspace- 213 * visible. We do this for consistency, and so 214 * that we can do debugging checks at __fput() 215 */ 216 if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) { 217 file_take_write(file); 218 error = mnt_want_write(mnt); 219 WARN_ON(error); 220 } 221 return error; 222 } 223 EXPORT_SYMBOL(init_file); 224 225 void fput(struct file *file) 226 { 227 if (atomic_long_dec_and_test(&file->f_count)) 228 __fput(file); 229 } 230 231 EXPORT_SYMBOL(fput); 232 233 /** 234 * drop_file_write_access - give up ability to write to a file 235 * @file: the file to which we will stop writing 236 * 237 * This is a central place which will give up the ability 238 * to write to @file, along with access to write through 239 * its vfsmount. 240 */ 241 void drop_file_write_access(struct file *file) 242 { 243 struct vfsmount *mnt = file->f_path.mnt; 244 struct dentry *dentry = file->f_path.dentry; 245 struct inode *inode = dentry->d_inode; 246 247 put_write_access(inode); 248 249 if (special_file(inode->i_mode)) 250 return; 251 if (file_check_writeable(file) != 0) 252 return; 253 mnt_drop_write(mnt); 254 file_release_write(file); 255 } 256 EXPORT_SYMBOL_GPL(drop_file_write_access); 257 258 /* __fput is called from task context when aio completion releases the last 259 * last use of a struct file *. Do not use otherwise. 260 */ 261 void __fput(struct file *file) 262 { 263 struct dentry *dentry = file->f_path.dentry; 264 struct vfsmount *mnt = file->f_path.mnt; 265 struct inode *inode = dentry->d_inode; 266 267 might_sleep(); 268 269 fsnotify_close(file); 270 /* 271 * The function eventpoll_release() should be the first called 272 * in the file cleanup chain. 273 */ 274 eventpoll_release(file); 275 locks_remove_flock(file); 276 277 if (unlikely(file->f_flags & FASYNC)) { 278 if (file->f_op && file->f_op->fasync) 279 file->f_op->fasync(-1, file, 0); 280 } 281 if (file->f_op && file->f_op->release) 282 file->f_op->release(inode, file); 283 security_file_free(file); 284 ima_file_free(file); 285 if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL)) 286 cdev_put(inode->i_cdev); 287 fops_put(file->f_op); 288 put_pid(file->f_owner.pid); 289 file_kill(file); 290 if (file->f_mode & FMODE_WRITE) 291 drop_file_write_access(file); 292 file->f_path.dentry = NULL; 293 file->f_path.mnt = NULL; 294 file_free(file); 295 dput(dentry); 296 mntput(mnt); 297 } 298 299 struct file *fget(unsigned int fd) 300 { 301 struct file *file; 302 struct files_struct *files = current->files; 303 304 rcu_read_lock(); 305 file = fcheck_files(files, fd); 306 if (file) { 307 if (!atomic_long_inc_not_zero(&file->f_count)) { 308 /* File object ref couldn't be taken */ 309 rcu_read_unlock(); 310 return NULL; 311 } 312 } 313 rcu_read_unlock(); 314 315 return file; 316 } 317 318 EXPORT_SYMBOL(fget); 319 320 /* 321 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 322 * You can use this only if it is guranteed that the current task already 323 * holds a refcnt to that file. That check has to be done at fget() only 324 * and a flag is returned to be passed to the corresponding fput_light(). 325 * There must not be a cloning between an fget_light/fput_light pair. 326 */ 327 struct file *fget_light(unsigned int fd, int *fput_needed) 328 { 329 struct file *file; 330 struct files_struct *files = current->files; 331 332 *fput_needed = 0; 333 if (likely((atomic_read(&files->count) == 1))) { 334 file = fcheck_files(files, fd); 335 } else { 336 rcu_read_lock(); 337 file = fcheck_files(files, fd); 338 if (file) { 339 if (atomic_long_inc_not_zero(&file->f_count)) 340 *fput_needed = 1; 341 else 342 /* Didn't get the reference, someone's freed */ 343 file = NULL; 344 } 345 rcu_read_unlock(); 346 } 347 348 return file; 349 } 350 351 352 void put_filp(struct file *file) 353 { 354 if (atomic_long_dec_and_test(&file->f_count)) { 355 security_file_free(file); 356 file_kill(file); 357 file_free(file); 358 } 359 } 360 361 void file_move(struct file *file, struct list_head *list) 362 { 363 if (!list) 364 return; 365 file_list_lock(); 366 list_move(&file->f_u.fu_list, list); 367 file_list_unlock(); 368 } 369 370 void file_kill(struct file *file) 371 { 372 if (!list_empty(&file->f_u.fu_list)) { 373 file_list_lock(); 374 list_del_init(&file->f_u.fu_list); 375 file_list_unlock(); 376 } 377 } 378 379 int fs_may_remount_ro(struct super_block *sb) 380 { 381 struct file *file; 382 383 /* Check that no files are currently opened for writing. */ 384 file_list_lock(); 385 list_for_each_entry(file, &sb->s_files, f_u.fu_list) { 386 struct inode *inode = file->f_path.dentry->d_inode; 387 388 /* File with pending delete? */ 389 if (inode->i_nlink == 0) 390 goto too_bad; 391 392 /* Writeable file? */ 393 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 394 goto too_bad; 395 } 396 file_list_unlock(); 397 return 1; /* Tis' cool bro. */ 398 too_bad: 399 file_list_unlock(); 400 return 0; 401 } 402 403 void __init files_init(unsigned long mempages) 404 { 405 int n; 406 407 filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, 408 SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); 409 410 /* 411 * One file with associated inode and dcache is very roughly 1K. 412 * Per default don't use more than 10% of our memory for files. 413 */ 414 415 n = (mempages * (PAGE_SIZE / 1024)) / 10; 416 files_stat.max_files = n; 417 if (files_stat.max_files < NR_FILE) 418 files_stat.max_files = NR_FILE; 419 files_defer_init(); 420 percpu_counter_init(&nr_files, 0); 421 } 422