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