fs/file_table.c

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