fs/file_table.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/fs/file_table.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
   7  */
   8
   9 #include <linux/string.h>
  10 #include <linux/slab.h>
  11 #include <linux/file.h>
  12 #include <linux/fdtable.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/fs.h>
  16 #include <linux/security.h>
  17 #include <linux/cred.h>
  18 #include <linux/eventpoll.h>
  19 #include <linux/rcupdate.h>
  20 #include <linux/mount.h>
  21 #include <linux/capability.h>
  22 #include <linux/cdev.h>
  23 #include <linux/fsnotify.h>
  24 #include <linux/sysctl.h>
  25 #include <linux/percpu_counter.h>
  26 #include <linux/percpu.h>
  27 #include <linux/task_work.h>
  28 #include <linux/ima.h>
  29 #include <linux/swap.h>
  30
  31 #include <linux/atomic.h>
  32
  33 #include "internal.h"
  34
  35 /* sysctl tunables... */
  36 struct files_stat_struct files_stat = {
  37         .max_files = NR_FILE
  38 };
  39
  40 /* SLAB cache for file structures */
  41 static struct kmem_cache *filp_cachep __read_mostly;
  42
  43 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  44
  45 static void file_free_rcu(struct rcu_head *head)
  46 {
  47         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  48
  49         put_cred(f->f_cred);
  50         kmem_cache_free(filp_cachep, f);
  51 }
  52
  53 static inline void file_free(struct file *f)
  54 {
  55         security_file_free(f);
  56         if (!(f->f_mode & FMODE_NOACCOUNT))
  57                 percpu_counter_dec(&nr_files);
  58         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  59 }
  60
  61 /*
  62  * Return the total number of open files in the system
  63  */
  64 static long get_nr_files(void)
  65 {
  66         return percpu_counter_read_positive(&nr_files);
  67 }
  68
  69 /*
  70  * Return the maximum number of open files in the system
  71  */
  72 unsigned long get_max_files(void)
  73 {
  74         return files_stat.max_files;
  75 }
  76 EXPORT_SYMBOL_GPL(get_max_files);
  77
  78 /*
  79  * Handle nr_files sysctl
  80  */
  81 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  82 int proc_nr_files(struct ctl_table *table, int write,
  83                      void __user *buffer, size_t *lenp, loff_t *ppos)
  84 {
  85         files_stat.nr_files = get_nr_files();
  86         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  87 }
  88 #else
  89 int proc_nr_files(struct ctl_table *table, int write,
  90                      void __user *buffer, size_t *lenp, loff_t *ppos)
  91 {
  92         return -ENOSYS;
  93 }
  94 #endif
  95
  96 static struct file *__alloc_file(int flags, const struct cred *cred)
  97 {
  98         struct file *f;
  99         int error;
 100
 101         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 102         if (unlikely(!f))
 103                 return ERR_PTR(-ENOMEM);
 104
 105         f->f_cred = get_cred(cred);
 106         error = security_file_alloc(f);
 107         if (unlikely(error)) {
 108                 file_free_rcu(&f->f_u.fu_rcuhead);
 109                 return ERR_PTR(error);
 110         }
 111
 112         atomic_long_set(&f->f_count, 1);
 113         rwlock_init(&f->f_owner.lock);
 114         spin_lock_init(&f->f_lock);
 115         mutex_init(&f->f_pos_lock);
 116         eventpoll_init_file(f);
 117         f->f_flags = flags;
 118         f->f_mode = OPEN_FMODE(flags);
 119         /* f->f_version: 0 */
 120
 121         return f;
 122 }
 123
 124 /* Find an unused file structure and return a pointer to it.
 125  * Returns an error pointer if some error happend e.g. we over file
 126  * structures limit, run out of memory or operation is not permitted.
 127  *
 128  * Be very careful using this.  You are responsible for
 129  * getting write access to any mount that you might assign
 130  * to this filp, if it is opened for write.  If this is not
 131  * done, you will imbalance int the mount's writer count
 132  * and a warning at __fput() time.
 133  */
 134 struct file *alloc_empty_file(int flags, const struct cred *cred)
 135 {
 136         static long old_max;
 137         struct file *f;
 138
 139         /*
 140          * Privileged users can go above max_files
 141          */
 142         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 143                 /*
 144                  * percpu_counters are inaccurate.  Do an expensive check before
 145                  * we go and fail.
 146                  */
 147                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 148                         goto over;
 149         }
 150
 151         f = __alloc_file(flags, cred);
 152         if (!IS_ERR(f))
 153                 percpu_counter_inc(&nr_files);
 154
 155         return f;
 156
 157 over:
 158         /* Ran out of filps - report that */
 159         if (get_nr_files() > old_max) {
 160                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 161                 old_max = get_nr_files();
 162         }
 163         return ERR_PTR(-ENFILE);
 164 }
 165
 166 /*
 167  * Variant of alloc_empty_file() that doesn't check and modify nr_files.
 168  *
 169  * Should not be used unless there's a very good reason to do so.
 170  */
 171 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 172 {
 173         struct file *f = __alloc_file(flags, cred);
 174
 175         if (!IS_ERR(f))
 176                 f->f_mode |= FMODE_NOACCOUNT;
 177
 178         return f;
 179 }
 180
 181 /**
 182  * alloc_file - allocate and initialize a 'struct file'
 183  *
 184  * @path: the (dentry, vfsmount) pair for the new file
 185  * @flags: O_... flags with which the new file will be opened
 186  * @fop: the 'struct file_operations' for the new file
 187  */
 188 static struct file *alloc_file(const struct path *path, int flags,
 189                 const struct file_operations *fop)
 190 {
 191         struct file *file;
 192
 193         file = alloc_empty_file(flags, current_cred());
 194         if (IS_ERR(file))
 195                 return file;
 196
 197         file->f_path = *path;
 198         file->f_inode = path->dentry->d_inode;
 199         file->f_mapping = path->dentry->d_inode->i_mapping;
 200         file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
 201         if ((file->f_mode & FMODE_READ) &&
 202              likely(fop->read || fop->read_iter))
 203                 file->f_mode |= FMODE_CAN_READ;
 204         if ((file->f_mode & FMODE_WRITE) &&
 205              likely(fop->write || fop->write_iter))
 206                 file->f_mode |= FMODE_CAN_WRITE;
 207         file->f_mode |= FMODE_OPENED;
 208         file->f_op = fop;
 209         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 210                 i_readcount_inc(path->dentry->d_inode);
 211         return file;
 212 }
 213
 214 struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
 215                                 const char *name, int flags,
 216                                 const struct file_operations *fops)
 217 {
 218         static const struct dentry_operations anon_ops = {
 219                 .d_dname = simple_dname
 220         };
 221         struct qstr this = QSTR_INIT(name, strlen(name));
 222         struct path path;
 223         struct file *file;
 224
 225         path.dentry = d_alloc_pseudo(mnt->mnt_sb, &this);
 226         if (!path.dentry)
 227                 return ERR_PTR(-ENOMEM);
 228         if (!mnt->mnt_sb->s_d_op)
 229                 d_set_d_op(path.dentry, &anon_ops);
 230         path.mnt = mntget(mnt);
 231         d_instantiate(path.dentry, inode);
 232         file = alloc_file(&path, flags, fops);
 233         if (IS_ERR(file)) {
 234                 ihold(inode);
 235                 path_put(&path);
 236         }
 237         return file;
 238 }
 239 EXPORT_SYMBOL(alloc_file_pseudo);
 240
 241 struct file *alloc_file_clone(struct file *base, int flags,
 242                                 const struct file_operations *fops)
 243 {
 244         struct file *f = alloc_file(&base->f_path, flags, fops);
 245         if (!IS_ERR(f)) {
 246                 path_get(&f->f_path);
 247                 f->f_mapping = base->f_mapping;
 248         }
 249         return f;
 250 }
 251
 252 /* the real guts of fput() - releasing the last reference to file
 253  */
 254 static void __fput(struct file *file)
 255 {
 256         struct dentry *dentry = file->f_path.dentry;
 257         struct vfsmount *mnt = file->f_path.mnt;
 258         struct inode *inode = file->f_inode;
 259         fmode_t mode = file->f_mode;
 260
 261         if (unlikely(!(file->f_mode & FMODE_OPENED)))
 262                 goto out;
 263
 264         might_sleep();
 265
 266         fsnotify_close(file);
 267         /*
 268          * The function eventpoll_release() should be the first called
 269          * in the file cleanup chain.
 270          */
 271         eventpoll_release(file);
 272         locks_remove_file(file);
 273
 274         ima_file_free(file);
 275         if (unlikely(file->f_flags & FASYNC)) {
 276                 if (file->f_op->fasync)
 277                         file->f_op->fasync(-1, file, 0);
 278         }
 279         if (file->f_op->release)
 280                 file->f_op->release(inode, file);
 281         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 282                      !(mode & FMODE_PATH))) {
 283                 cdev_put(inode->i_cdev);
 284         }
 285         fops_put(file->f_op);
 286         put_pid(file->f_owner.pid);
 287         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 288                 i_readcount_dec(inode);
 289         if (mode & FMODE_WRITER) {
 290                 put_write_access(inode);
 291                 __mnt_drop_write(mnt);
 292         }
 293         dput(dentry);
 294         if (unlikely(mode & FMODE_NEED_UNMOUNT))
 295                 dissolve_on_fput(mnt);
 296         mntput(mnt);
 297 out:
 298         file_free(file);
 299 }
 300
 301 static LLIST_HEAD(delayed_fput_list);
 302 static void delayed_fput(struct work_struct *unused)
 303 {
 304         struct llist_node *node = llist_del_all(&delayed_fput_list);
 305         struct file *f, *t;
 306
 307         llist_for_each_entry_safe(f, t, node, f_u.fu_llist)
 308                 __fput(f);
 309 }
 310
 311 static void ____fput(struct callback_head *work)
 312 {
 313         __fput(container_of(work, struct file, f_u.fu_rcuhead));
 314 }
 315
 316 /*
 317  * If kernel thread really needs to have the final fput() it has done
 318  * to complete, call this.  The only user right now is the boot - we
 319  * *do* need to make sure our writes to binaries on initramfs has
 320  * not left us with opened struct file waiting for __fput() - execve()
 321  * won't work without that.  Please, don't add more callers without
 322  * very good reasons; in particular, never call that with locks
 323  * held and never call that from a thread that might need to do
 324  * some work on any kind of umount.
 325  */
 326 void flush_delayed_fput(void)
 327 {
 328         delayed_fput(NULL);
 329 }
 330
 331 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 332
 333 void fput_many(struct file *file, unsigned int refs)
 334 {
 335         if (atomic_long_sub_and_test(refs, &file->f_count)) {
 336                 struct task_struct *task = current;
 337
 338                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 339                         init_task_work(&file->f_u.fu_rcuhead, ____fput);
 340                         if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
 341                                 return;
 342                         /*
 343                          * After this task has run exit_task_work(),
 344                          * task_work_add() will fail.  Fall through to delayed
 345                          * fput to avoid leaking *file.
 346                          */
 347                 }
 348
 349                 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
 350                         schedule_delayed_work(&delayed_fput_work, 1);
 351         }
 352 }
 353
 354 void fput(struct file *file)
 355 {
 356         fput_many(file, 1);
 357 }
 358
 359 /*
 360  * synchronous analog of fput(); for kernel threads that might be needed
 361  * in some umount() (and thus can't use flush_delayed_fput() without
 362  * risking deadlocks), need to wait for completion of __fput() and know
 363  * for this specific struct file it won't involve anything that would
 364  * need them.  Use only if you really need it - at the very least,
 365  * don't blindly convert fput() by kernel thread to that.
 366  */
 367 void __fput_sync(struct file *file)
 368 {
 369         if (atomic_long_dec_and_test(&file->f_count)) {
 370                 struct task_struct *task = current;
 371                 BUG_ON(!(task->flags & PF_KTHREAD));
 372                 __fput(file);
 373         }
 374 }
 375
 376 EXPORT_SYMBOL(fput);
 377
 378 void __init files_init(void)
 379 {
 380         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 381                         SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
 382         percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 383 }
 384
 385 /*
 386  * One file with associated inode and dcache is very roughly 1K. Per default
 387  * do not use more than 10% of our memory for files.
 388  */
 389 void __init files_maxfiles_init(void)
 390 {
 391         unsigned long n;
 392         unsigned long nr_pages = totalram_pages();
 393         unsigned long memreserve = (nr_pages - nr_free_pages()) * 3/2;
 394
 395         memreserve = min(memreserve, nr_pages - 1);
 396         n = ((nr_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
 397
 398         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 399 }