| 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 | * |
| 154 | * @path: the (dentry, vfsmount) pair for 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 | struct file *alloc_file(struct path *path, fmode_t mode, |
| 159 | const struct file_operations *fop) |
| 160 | { |
| 161 | struct file *file; |
| 162 | |
| 163 | file = get_empty_filp(); |
| 164 | if (IS_ERR(file)) |
| 165 | return file; |
| 166 | |
| 167 | file->f_path = *path; |
| 168 | file->f_inode = path->dentry->d_inode; |
| 169 | file->f_mapping = path->dentry->d_inode->i_mapping; |
| 170 | if ((mode & FMODE_READ) && |
| 171 | likely(fop->read || fop->aio_read || fop->read_iter)) |
| 172 | mode |= FMODE_CAN_READ; |
| 173 | if ((mode & FMODE_WRITE) && |
| 174 | likely(fop->write || fop->aio_write || fop->write_iter)) |
| 175 | mode |= FMODE_CAN_WRITE; |
| 176 | file->f_mode = mode; |
| 177 | file->f_op = fop; |
| 178 | if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) |
| 179 | i_readcount_inc(path->dentry->d_inode); |
| 180 | return file; |
| 181 | } |
| 182 | EXPORT_SYMBOL(alloc_file); |
| 183 | |
| 184 | /* the real guts of fput() - releasing the last reference to file |
| 185 | */ |
| 186 | static void __fput(struct file *file) |
| 187 | { |
| 188 | struct dentry *dentry = file->f_path.dentry; |
| 189 | struct vfsmount *mnt = file->f_path.mnt; |
| 190 | struct inode *inode = file->f_inode; |
| 191 | |
| 192 | might_sleep(); |
| 193 | |
| 194 | fsnotify_close(file); |
| 195 | /* |
| 196 | * The function eventpoll_release() should be the first called |
| 197 | * in the file cleanup chain. |
| 198 | */ |
| 199 | eventpoll_release(file); |
| 200 | locks_remove_file(file); |
| 201 | |
| 202 | if (unlikely(file->f_flags & FASYNC)) { |
| 203 | if (file->f_op->fasync) |
| 204 | file->f_op->fasync(-1, file, 0); |
| 205 | } |
| 206 | ima_file_free(file); |
| 207 | if (file->f_op->release) |
| 208 | file->f_op->release(inode, file); |
| 209 | security_file_free(file); |
| 210 | if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL && |
| 211 | !(file->f_mode & FMODE_PATH))) { |
| 212 | cdev_put(inode->i_cdev); |
| 213 | } |
| 214 | fops_put(file->f_op); |
| 215 | put_pid(file->f_owner.pid); |
| 216 | if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) |
| 217 | i_readcount_dec(inode); |
| 218 | if (file->f_mode & FMODE_WRITER) { |
| 219 | put_write_access(inode); |
| 220 | __mnt_drop_write(mnt); |
| 221 | } |
| 222 | file->f_path.dentry = NULL; |
| 223 | file->f_path.mnt = NULL; |
| 224 | file->f_inode = NULL; |
| 225 | file_free(file); |
| 226 | dput(dentry); |
| 227 | mntput(mnt); |
| 228 | } |
| 229 | |
| 230 | static LLIST_HEAD(delayed_fput_list); |
| 231 | static void delayed_fput(struct work_struct *unused) |
| 232 | { |
| 233 | struct llist_node *node = llist_del_all(&delayed_fput_list); |
| 234 | struct llist_node *next; |
| 235 | |
| 236 | for (; node; node = next) { |
| 237 | next = llist_next(node); |
| 238 | __fput(llist_entry(node, struct file, f_u.fu_llist)); |
| 239 | } |
| 240 | } |
| 241 | |
| 242 | static void ____fput(struct callback_head *work) |
| 243 | { |
| 244 | __fput(container_of(work, struct file, f_u.fu_rcuhead)); |
| 245 | } |
| 246 | |
| 247 | /* |
| 248 | * If kernel thread really needs to have the final fput() it has done |
| 249 | * to complete, call this. The only user right now is the boot - we |
| 250 | * *do* need to make sure our writes to binaries on initramfs has |
| 251 | * not left us with opened struct file waiting for __fput() - execve() |
| 252 | * won't work without that. Please, don't add more callers without |
| 253 | * very good reasons; in particular, never call that with locks |
| 254 | * held and never call that from a thread that might need to do |
| 255 | * some work on any kind of umount. |
| 256 | */ |
| 257 | void flush_delayed_fput(void) |
| 258 | { |
| 259 | delayed_fput(NULL); |
| 260 | } |
| 261 | |
| 262 | static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput); |
| 263 | |
| 264 | void fput(struct file *file) |
| 265 | { |
| 266 | if (atomic_long_dec_and_test(&file->f_count)) { |
| 267 | struct task_struct *task = current; |
| 268 | |
| 269 | if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) { |
| 270 | init_task_work(&file->f_u.fu_rcuhead, ____fput); |
| 271 | if (!task_work_add(task, &file->f_u.fu_rcuhead, true)) |
| 272 | return; |
| 273 | /* |
| 274 | * After this task has run exit_task_work(), |
| 275 | * task_work_add() will fail. Fall through to delayed |
| 276 | * fput to avoid leaking *file. |
| 277 | */ |
| 278 | } |
| 279 | |
| 280 | if (llist_add(&file->f_u.fu_llist, &delayed_fput_list)) |
| 281 | schedule_delayed_work(&delayed_fput_work, 1); |
| 282 | } |
| 283 | } |
| 284 | |
| 285 | /* |
| 286 | * synchronous analog of fput(); for kernel threads that might be needed |
| 287 | * in some umount() (and thus can't use flush_delayed_fput() without |
| 288 | * risking deadlocks), need to wait for completion of __fput() and know |
| 289 | * for this specific struct file it won't involve anything that would |
| 290 | * need them. Use only if you really need it - at the very least, |
| 291 | * don't blindly convert fput() by kernel thread to that. |
| 292 | */ |
| 293 | void __fput_sync(struct file *file) |
| 294 | { |
| 295 | if (atomic_long_dec_and_test(&file->f_count)) { |
| 296 | struct task_struct *task = current; |
| 297 | BUG_ON(!(task->flags & PF_KTHREAD)); |
| 298 | __fput(file); |
| 299 | } |
| 300 | } |
| 301 | |
| 302 | EXPORT_SYMBOL(fput); |
| 303 | |
| 304 | void put_filp(struct file *file) |
| 305 | { |
| 306 | if (atomic_long_dec_and_test(&file->f_count)) { |
| 307 | security_file_free(file); |
| 308 | file_free(file); |
| 309 | } |
| 310 | } |
| 311 | |
| 312 | void __init files_init(unsigned long mempages) |
| 313 | { |
| 314 | unsigned long n; |
| 315 | |
| 316 | filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, |
| 317 | SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); |
| 318 | |
| 319 | /* |
| 320 | * One file with associated inode and dcache is very roughly 1K. |
| 321 | * Per default don't use more than 10% of our memory for files. |
| 322 | */ |
| 323 | |
| 324 | n = (mempages * (PAGE_SIZE / 1024)) / 10; |
| 325 | files_stat.max_files = max_t(unsigned long, n, NR_FILE); |
| 326 | percpu_counter_init(&nr_files, 0, GFP_KERNEL); |
| 327 | } |