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/eventpoll.h> 17 #include <linux/rcupdate.h> 18 #include <linux/mount.h> 19 #include <linux/capability.h> 20 #include <linux/cdev.h> 21 #include <linux/fsnotify.h> 22 #include <linux/sysctl.h> 23 #include <linux/lglock.h> 24 #include <linux/percpu_counter.h> 25 #include <linux/percpu.h> 26 #include <linux/hardirq.h> 27 #include <linux/task_work.h> 28 #include <linux/ima.h> 29 30 #include <linux/atomic.h> 31 32 #include "internal.h" 33 34 /* sysctl tunables... */ 35 struct files_stat_struct files_stat = { 36 .max_files = NR_FILE 37 }; 38 39 /* SLAB cache for file structures */ 40 static struct kmem_cache *filp_cachep __read_mostly; 41 42 static struct percpu_counter nr_files __cacheline_aligned_in_smp; 43 44 static void file_free_rcu(struct rcu_head *head) 45 { 46 struct file *f = container_of(head, struct file, f_u.fu_rcuhead); 47 48 put_cred(f->f_cred); 49 kmem_cache_free(filp_cachep, f); 50 } 51 52 static inline void file_free(struct file *f) 53 { 54 percpu_counter_dec(&nr_files); 55 call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); 56 } 57 58 /* 59 * Return the total number of open files in the system 60 */ 61 static long get_nr_files(void) 62 { 63 return percpu_counter_read_positive(&nr_files); 64 } 65 66 /* 67 * Return the maximum number of open files in the system 68 */ 69 unsigned long get_max_files(void) 70 { 71 return files_stat.max_files; 72 } 73 EXPORT_SYMBOL_GPL(get_max_files); 74 75 /* 76 * Handle nr_files sysctl 77 */ 78 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) 79 int proc_nr_files(struct ctl_table *table, int write, 80 void __user *buffer, size_t *lenp, loff_t *ppos) 81 { 82 files_stat.nr_files = get_nr_files(); 83 return proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 84 } 85 #else 86 int proc_nr_files(struct ctl_table *table, int write, 87 void __user *buffer, size_t *lenp, loff_t *ppos) 88 { 89 return -ENOSYS; 90 } 91 #endif 92 93 /* Find an unused file structure and return a pointer to it. 94 * Returns an error pointer if some error happend e.g. we over file 95 * structures limit, run out of memory or operation is not permitted. 96 * 97 * Be very careful using this. You are responsible for 98 * getting write access to any mount that you might assign 99 * to this filp, if it is opened for write. If this is not 100 * done, you will imbalance int the mount's writer count 101 * and a warning at __fput() time. 102 */ 103 struct file *get_empty_filp(void) 104 { 105 const struct cred *cred = current_cred(); 106 static long old_max; 107 struct file *f; 108 int error; 109 110 /* 111 * Privileged users can go above max_files 112 */ 113 if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { 114 /* 115 * percpu_counters are inaccurate. Do an expensive check before 116 * we go and fail. 117 */ 118 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files) 119 goto over; 120 } 121 122 f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); 123 if (unlikely(!f)) 124 return ERR_PTR(-ENOMEM); 125 126 percpu_counter_inc(&nr_files); 127 f->f_cred = get_cred(cred); 128 error = security_file_alloc(f); 129 if (unlikely(error)) { 130 file_free(f); 131 return ERR_PTR(error); 132 } 133 134 atomic_long_set(&f->f_count, 1); 135 rwlock_init(&f->f_owner.lock); 136 spin_lock_init(&f->f_lock); 137 mutex_init(&f->f_pos_lock); 138 eventpoll_init_file(f); 139 /* f->f_version: 0 */ 140 return f; 141 142 over: 143 /* Ran out of filps - report that */ 144 if (get_nr_files() > old_max) { 145 pr_info("VFS: file-max limit %lu reached\n", get_max_files()); 146 old_max = get_nr_files(); 147 } 148 return ERR_PTR(-ENFILE); 149 } 150 151 /** 152 * alloc_file - allocate and initialize a 'struct file' 153 * @mnt: the vfsmount on which the file will reside 154 * @dentry: the dentry representing the new file 155 * @mode: the mode with which the new file will be opened 156 * @fop: the 'struct file_operations' for the new file 157 * 158 * Use this instead of get_empty_filp() to get a new 159 * 'struct file'. Do so because of the same initialization 160 * pitfalls reasons listed for init_file(). This is a 161 * preferred interface to using init_file(). 162 * 163 * If all the callers of init_file() are eliminated, its 164 * code should be moved into this function. 165 */ 166 struct file *alloc_file(struct path *path, fmode_t mode, 167 const struct file_operations *fop) 168 { 169 struct file *file; 170 171 file = get_empty_filp(); 172 if (IS_ERR(file)) 173 return file; 174 175 file->f_path = *path; 176 file->f_inode = path->dentry->d_inode; 177 file->f_mapping = path->dentry->d_inode->i_mapping; 178 if ((mode & FMODE_READ) && 179 likely(fop->read || fop->aio_read || fop->read_iter)) 180 mode |= FMODE_CAN_READ; 181 if ((mode & FMODE_WRITE) && 182 likely(fop->write || fop->aio_write || fop->write_iter)) 183 mode |= FMODE_CAN_WRITE; 184 file->f_mode = mode; 185 file->f_op = fop; 186 if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) 187 i_readcount_inc(path->dentry->d_inode); 188 return file; 189 } 190 EXPORT_SYMBOL(alloc_file); 191 192 /* the real guts of fput() - releasing the last reference to file 193 */ 194 static void __fput(struct file *file) 195 { 196 struct dentry *dentry = file->f_path.dentry; 197 struct vfsmount *mnt = file->f_path.mnt; 198 struct inode *inode = file->f_inode; 199 200 might_sleep(); 201 202 fsnotify_close(file); 203 /* 204 * The function eventpoll_release() should be the first called 205 * in the file cleanup chain. 206 */ 207 eventpoll_release(file); 208 locks_remove_file(file); 209 210 if (unlikely(file->f_flags & FASYNC)) { 211 if (file->f_op->fasync) 212 file->f_op->fasync(-1, file, 0); 213 } 214 ima_file_free(file); 215 if (file->f_op->release) 216 file->f_op->release(inode, file); 217 security_file_free(file); 218 if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL && 219 !(file->f_mode & FMODE_PATH))) { 220 cdev_put(inode->i_cdev); 221 } 222 fops_put(file->f_op); 223 put_pid(file->f_owner.pid); 224 if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) 225 i_readcount_dec(inode); 226 if (file->f_mode & FMODE_WRITER) { 227 put_write_access(inode); 228 __mnt_drop_write(mnt); 229 } 230 file->f_path.dentry = NULL; 231 file->f_path.mnt = NULL; 232 file->f_inode = NULL; 233 file_free(file); 234 dput(dentry); 235 mntput(mnt); 236 } 237 238 static LLIST_HEAD(delayed_fput_list); 239 static void delayed_fput(struct work_struct *unused) 240 { 241 struct llist_node *node = llist_del_all(&delayed_fput_list); 242 struct llist_node *next; 243 244 for (; node; node = next) { 245 next = llist_next(node); 246 __fput(llist_entry(node, struct file, f_u.fu_llist)); 247 } 248 } 249 250 static void ____fput(struct callback_head *work) 251 { 252 __fput(container_of(work, struct file, f_u.fu_rcuhead)); 253 } 254 255 /* 256 * If kernel thread really needs to have the final fput() it has done 257 * to complete, call this. The only user right now is the boot - we 258 * *do* need to make sure our writes to binaries on initramfs has 259 * not left us with opened struct file waiting for __fput() - execve() 260 * won't work without that. Please, don't add more callers without 261 * very good reasons; in particular, never call that with locks 262 * held and never call that from a thread that might need to do 263 * some work on any kind of umount. 264 */ 265 void flush_delayed_fput(void) 266 { 267 delayed_fput(NULL); 268 } 269 270 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput); 271 272 void fput(struct file *file) 273 { 274 if (atomic_long_dec_and_test(&file->f_count)) { 275 struct task_struct *task = current; 276 277 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) { 278 init_task_work(&file->f_u.fu_rcuhead, ____fput); 279 if (!task_work_add(task, &file->f_u.fu_rcuhead, true)) 280 return; 281 /* 282 * After this task has run exit_task_work(), 283 * task_work_add() will fail. Fall through to delayed 284 * fput to avoid leaking *file. 285 */ 286 } 287 288 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list)) 289 schedule_delayed_work(&delayed_fput_work, 1); 290 } 291 } 292 293 /* 294 * synchronous analog of fput(); for kernel threads that might be needed 295 * in some umount() (and thus can't use flush_delayed_fput() without 296 * risking deadlocks), need to wait for completion of __fput() and know 297 * for this specific struct file it won't involve anything that would 298 * need them. Use only if you really need it - at the very least, 299 * don't blindly convert fput() by kernel thread to that. 300 */ 301 void __fput_sync(struct file *file) 302 { 303 if (atomic_long_dec_and_test(&file->f_count)) { 304 struct task_struct *task = current; 305 BUG_ON(!(task->flags & PF_KTHREAD)); 306 __fput(file); 307 } 308 } 309 310 EXPORT_SYMBOL(fput); 311 312 void put_filp(struct file *file) 313 { 314 if (atomic_long_dec_and_test(&file->f_count)) { 315 security_file_free(file); 316 file_free(file); 317 } 318 } 319 320 void __init files_init(unsigned long mempages) 321 { 322 unsigned long n; 323 324 filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, 325 SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); 326 327 /* 328 * One file with associated inode and dcache is very roughly 1K. 329 * Per default don't use more than 10% of our memory for files. 330 */ 331 332 n = (mempages * (PAGE_SIZE / 1024)) / 10; 333 files_stat.max_files = max_t(unsigned long, n, NR_FILE); 334 percpu_counter_init(&nr_files, 0); 335 } 336