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 #include <linux/kmemleak.h>
  31
  32 #include <linux/atomic.h>
  33
  34 #include "internal.h"
  35
  36 /* sysctl tunables... */
  37 static struct files_stat_struct files_stat = {
  38         .max_files = NR_FILE
  39 };
  40
  41 /* SLAB cache for file structures */
  42 static struct kmem_cache *filp_cachep __read_mostly;
  43
  44 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  45
  46 static void file_free_rcu(struct rcu_head *head)
  47 {
  48         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  49
  50         put_cred(f->f_cred);
  51         kmem_cache_free(filp_cachep, f);
  52 }
  53
  54 static inline void file_free(struct file *f)
  55 {
  56         security_file_free(f);
  57         if (!(f->f_mode & FMODE_NOACCOUNT))
  58                 percpu_counter_dec(&nr_files);
  59         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  60 }
  61
  62 /*
  63  * Return the total number of open files in the system
  64  */
  65 static long get_nr_files(void)
  66 {
  67         return percpu_counter_read_positive(&nr_files);
  68 }
  69
  70 /*
  71  * Return the maximum number of open files in the system
  72  */
  73 unsigned long get_max_files(void)
  74 {
  75         return files_stat.max_files;
  76 }
  77 EXPORT_SYMBOL_GPL(get_max_files);
  78
  79 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  80
  81 /*
  82  * Handle nr_files sysctl
  83  */
  84 static int proc_nr_files(struct ctl_table *table, int write, void *buffer,
  85                          size_t *lenp, loff_t *ppos)
  86 {
  87         files_stat.nr_files = get_nr_files();
  88         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  89 }
  90
  91 static struct ctl_table fs_stat_sysctls[] = {
  92         {
  93                 .procname       = "file-nr",
  94                 .data           = &files_stat,
  95                 .maxlen         = sizeof(files_stat),
  96                 .mode           = 0444,
  97                 .proc_handler   = proc_nr_files,
  98         },
  99         {
 100                 .procname       = "file-max",
 101                 .data           = &files_stat.max_files,
 102                 .maxlen         = sizeof(files_stat.max_files),
 103                 .mode           = 0644,
 104                 .proc_handler   = proc_doulongvec_minmax,
 105                 .extra1         = SYSCTL_LONG_ZERO,
 106                 .extra2         = SYSCTL_LONG_MAX,
 107         },
 108         {
 109                 .procname       = "nr_open",
 110                 .data           = &sysctl_nr_open,
 111                 .maxlen         = sizeof(unsigned int),
 112                 .mode           = 0644,
 113                 .proc_handler   = proc_dointvec_minmax,
 114                 .extra1         = &sysctl_nr_open_min,
 115                 .extra2         = &sysctl_nr_open_max,
 116         },
 117         { }
 118 };
 119
 120 static int __init init_fs_stat_sysctls(void)
 121 {
 122         register_sysctl_init("fs", fs_stat_sysctls);
 123         if (IS_ENABLED(CONFIG_BINFMT_MISC)) {
 124                 struct ctl_table_header *hdr;
 125                 hdr = register_sysctl_mount_point("fs/binfmt_misc");
 126                 kmemleak_not_leak(hdr);
 127         }
 128         return 0;
 129 }
 130 fs_initcall(init_fs_stat_sysctls);
 131 #endif
 132
 133 static struct file *__alloc_file(int flags, const struct cred *cred)
 134 {
 135         struct file *f;
 136         int error;
 137
 138         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 139         if (unlikely(!f))
 140                 return ERR_PTR(-ENOMEM);
 141
 142         f->f_cred = get_cred(cred);
 143         error = security_file_alloc(f);
 144         if (unlikely(error)) {
 145                 file_free_rcu(&f->f_u.fu_rcuhead);
 146                 return ERR_PTR(error);
 147         }
 148
 149         atomic_long_set(&f->f_count, 1);
 150         rwlock_init(&f->f_owner.lock);
 151         spin_lock_init(&f->f_lock);
 152         mutex_init(&f->f_pos_lock);
 153         f->f_flags = flags;
 154         f->f_mode = OPEN_FMODE(flags);
 155         /* f->f_version: 0 */
 156
 157         return f;
 158 }
 159
 160 /* Find an unused file structure and return a pointer to it.
 161  * Returns an error pointer if some error happend e.g. we over file
 162  * structures limit, run out of memory or operation is not permitted.
 163  *
 164  * Be very careful using this.  You are responsible for
 165  * getting write access to any mount that you might assign
 166  * to this filp, if it is opened for write.  If this is not
 167  * done, you will imbalance int the mount's writer count
 168  * and a warning at __fput() time.
 169  */
 170 struct file *alloc_empty_file(int flags, const struct cred *cred)
 171 {
 172         static long old_max;
 173         struct file *f;
 174
 175         /*
 176          * Privileged users can go above max_files
 177          */
 178         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 179                 /*
 180                  * percpu_counters are inaccurate.  Do an expensive check before
 181                  * we go and fail.
 182                  */
 183                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 184                         goto over;
 185         }
 186
 187         f = __alloc_file(flags, cred);
 188         if (!IS_ERR(f))
 189                 percpu_counter_inc(&nr_files);
 190
 191         return f;
 192
 193 over:
 194         /* Ran out of filps - report that */
 195         if (get_nr_files() > old_max) {
 196                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 197                 old_max = get_nr_files();
 198         }
 199         return ERR_PTR(-ENFILE);
 200 }
 201
 202 /*
 203  * Variant of alloc_empty_file() that doesn't check and modify nr_files.
 204  *
 205  * Should not be used unless there's a very good reason to do so.
 206  */
 207 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 208 {
 209         struct file *f = __alloc_file(flags, cred);
 210
 211         if (!IS_ERR(f))
 212                 f->f_mode |= FMODE_NOACCOUNT;
 213
 214         return f;
 215 }
 216
 217 /**
 218  * alloc_file - allocate and initialize a 'struct file'
 219  *
 220  * @path: the (dentry, vfsmount) pair for the new file
 221  * @flags: O_... flags with which the new file will be opened
 222  * @fop: the 'struct file_operations' for the new file
 223  */
 224 static struct file *alloc_file(const struct path *path, int flags,
 225                 const struct file_operations *fop)
 226 {
 227         struct file *file;
 228
 229         file = alloc_empty_file(flags, current_cred());
 230         if (IS_ERR(file))
 231                 return file;
 232
 233         file->f_path = *path;
 234         file->f_inode = path->dentry->d_inode;
 235         file->f_mapping = path->dentry->d_inode->i_mapping;
 236         file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
 237         file->f_sb_err = file_sample_sb_err(file);
 238         if ((file->f_mode & FMODE_READ) &&
 239              likely(fop->read || fop->read_iter))
 240                 file->f_mode |= FMODE_CAN_READ;
 241         if ((file->f_mode & FMODE_WRITE) &&
 242              likely(fop->write || fop->write_iter))
 243                 file->f_mode |= FMODE_CAN_WRITE;
 244         file->f_mode |= FMODE_OPENED;
 245         file->f_op = fop;
 246         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 247                 i_readcount_inc(path->dentry->d_inode);
 248         return file;
 249 }
 250
 251 struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
 252                                 const char *name, int flags,
 253                                 const struct file_operations *fops)
 254 {
 255         static const struct dentry_operations anon_ops = {
 256                 .d_dname = simple_dname
 257         };
 258         struct qstr this = QSTR_INIT(name, strlen(name));
 259         struct path path;
 260         struct file *file;
 261
 262         path.dentry = d_alloc_pseudo(mnt->mnt_sb, &this);
 263         if (!path.dentry)
 264                 return ERR_PTR(-ENOMEM);
 265         if (!mnt->mnt_sb->s_d_op)
 266                 d_set_d_op(path.dentry, &anon_ops);
 267         path.mnt = mntget(mnt);
 268         d_instantiate(path.dentry, inode);
 269         file = alloc_file(&path, flags, fops);
 270         if (IS_ERR(file)) {
 271                 ihold(inode);
 272                 path_put(&path);
 273         }
 274         return file;
 275 }
 276 EXPORT_SYMBOL(alloc_file_pseudo);
 277
 278 struct file *alloc_file_clone(struct file *base, int flags,
 279                                 const struct file_operations *fops)
 280 {
 281         struct file *f = alloc_file(&base->f_path, flags, fops);
 282         if (!IS_ERR(f)) {
 283                 path_get(&f->f_path);
 284                 f->f_mapping = base->f_mapping;
 285         }
 286         return f;
 287 }
 288
 289 /* the real guts of fput() - releasing the last reference to file
 290  */
 291 static void __fput(struct file *file)
 292 {
 293         struct dentry *dentry = file->f_path.dentry;
 294         struct vfsmount *mnt = file->f_path.mnt;
 295         struct inode *inode = file->f_inode;
 296         fmode_t mode = file->f_mode;
 297
 298         if (unlikely(!(file->f_mode & FMODE_OPENED)))
 299                 goto out;
 300
 301         might_sleep();
 302
 303         fsnotify_close(file);
 304         /*
 305          * The function eventpoll_release() should be the first called
 306          * in the file cleanup chain.
 307          */
 308         eventpoll_release(file);
 309         locks_remove_file(file);
 310
 311         ima_file_free(file);
 312         if (unlikely(file->f_flags & FASYNC)) {
 313                 if (file->f_op->fasync)
 314                         file->f_op->fasync(-1, file, 0);
 315         }
 316         if (file->f_op->release)
 317                 file->f_op->release(inode, file);
 318         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 319                      !(mode & FMODE_PATH))) {
 320                 cdev_put(inode->i_cdev);
 321         }
 322         fops_put(file->f_op);
 323         put_pid(file->f_owner.pid);
 324         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 325                 i_readcount_dec(inode);
 326         if (mode & FMODE_WRITER) {
 327                 put_write_access(inode);
 328                 __mnt_drop_write(mnt);
 329         }
 330         dput(dentry);
 331         if (unlikely(mode & FMODE_NEED_UNMOUNT))
 332                 dissolve_on_fput(mnt);
 333         mntput(mnt);
 334 out:
 335         file_free(file);
 336 }
 337
 338 static LLIST_HEAD(delayed_fput_list);
 339 static void delayed_fput(struct work_struct *unused)
 340 {
 341         struct llist_node *node = llist_del_all(&delayed_fput_list);
 342         struct file *f, *t;
 343
 344         llist_for_each_entry_safe(f, t, node, f_u.fu_llist)
 345                 __fput(f);
 346 }
 347
 348 static void ____fput(struct callback_head *work)
 349 {
 350         __fput(container_of(work, struct file, f_u.fu_rcuhead));
 351 }
 352
 353 /*
 354  * If kernel thread really needs to have the final fput() it has done
 355  * to complete, call this.  The only user right now is the boot - we
 356  * *do* need to make sure our writes to binaries on initramfs has
 357  * not left us with opened struct file waiting for __fput() - execve()
 358  * won't work without that.  Please, don't add more callers without
 359  * very good reasons; in particular, never call that with locks
 360  * held and never call that from a thread that might need to do
 361  * some work on any kind of umount.
 362  */
 363 void flush_delayed_fput(void)
 364 {
 365         delayed_fput(NULL);
 366 }
 367 EXPORT_SYMBOL_GPL(flush_delayed_fput);
 368
 369 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 370
 371 void fput(struct file *file)
 372 {
 373         if (atomic_long_dec_and_test(&file->f_count)) {
 374                 struct task_struct *task = current;
 375
 376                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 377                         init_task_work(&file->f_u.fu_rcuhead, ____fput);
 378                         if (!task_work_add(task, &file->f_u.fu_rcuhead, TWA_RESUME))
 379                                 return;
 380                         /*
 381                          * After this task has run exit_task_work(),
 382                          * task_work_add() will fail.  Fall through to delayed
 383                          * fput to avoid leaking *file.
 384                          */
 385                 }
 386
 387                 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
 388                         schedule_delayed_work(&delayed_fput_work, 1);
 389         }
 390 }
 391
 392 /*
 393  * synchronous analog of fput(); for kernel threads that might be needed
 394  * in some umount() (and thus can't use flush_delayed_fput() without
 395  * risking deadlocks), need to wait for completion of __fput() and know
 396  * for this specific struct file it won't involve anything that would
 397  * need them.  Use only if you really need it - at the very least,
 398  * don't blindly convert fput() by kernel thread to that.
 399  */
 400 void __fput_sync(struct file *file)
 401 {
 402         if (atomic_long_dec_and_test(&file->f_count)) {
 403                 struct task_struct *task = current;
 404                 BUG_ON(!(task->flags & PF_KTHREAD));
 405                 __fput(file);
 406         }
 407 }
 408
 409 EXPORT_SYMBOL(fput);
 410 EXPORT_SYMBOL(__fput_sync);
 411
 412 void __init files_init(void)
 413 {
 414         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 415                         SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
 416         percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 417 }
 418
 419 /*
 420  * One file with associated inode and dcache is very roughly 1K. Per default
 421  * do not use more than 10% of our memory for files.
 422  */
 423 void __init files_maxfiles_init(void)
 424 {
 425         unsigned long n;
 426         unsigned long nr_pages = totalram_pages();
 427         unsigned long memreserve = (nr_pages - nr_free_pages()) * 3/2;
 428
 429         memreserve = min(memreserve, nr_pages - 1);
 430         n = ((nr_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
 431
 432         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 433 }