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/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         file_check_state(f);
  56         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  57 }
  58
  59 /*
  60  * Return the total number of open files in the system
  61  */
  62 static long get_nr_files(void)
  63 {
  64         return percpu_counter_read_positive(&nr_files);
  65 }
  66
  67 /*
  68  * Return the maximum number of open files in the system
  69  */
  70 unsigned long get_max_files(void)
  71 {
  72         return files_stat.max_files;
  73 }
  74 EXPORT_SYMBOL_GPL(get_max_files);
  75
  76 /*
  77  * Handle nr_files sysctl
  78  */
  79 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  80 int proc_nr_files(ctl_table *table, int write,
  81                      void __user *buffer, size_t *lenp, loff_t *ppos)
  82 {
  83         files_stat.nr_files = get_nr_files();
  84         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  85 }
  86 #else
  87 int proc_nr_files(ctl_table *table, int write,
  88                      void __user *buffer, size_t *lenp, loff_t *ppos)
  89 {
  90         return -ENOSYS;
  91 }
  92 #endif
  93
  94 /* Find an unused file structure and return a pointer to it.
  95  * Returns an error pointer if some error happend e.g. we over file
  96  * structures limit, run out of memory or operation is not permitted.
  97  *
  98  * Be very careful using this.  You are responsible for
  99  * getting write access to any mount that you might assign
 100  * to this filp, if it is opened for write.  If this is not
 101  * done, you will imbalance int the mount's writer count
 102  * and a warning at __fput() time.
 103  */
 104 struct file *get_empty_filp(void)
 105 {
 106         const struct cred *cred = current_cred();
 107         static long old_max;
 108         struct file *f;
 109         int error;
 110
 111         /*
 112          * Privileged users can go above max_files
 113          */
 114         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 115                 /*
 116                  * percpu_counters are inaccurate.  Do an expensive check before
 117                  * we go and fail.
 118                  */
 119                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 120                         goto over;
 121         }
 122
 123         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 124         if (unlikely(!f))
 125                 return ERR_PTR(-ENOMEM);
 126
 127         percpu_counter_inc(&nr_files);
 128         f->f_cred = get_cred(cred);
 129         error = security_file_alloc(f);
 130         if (unlikely(error)) {
 131                 file_free(f);
 132                 return ERR_PTR(error);
 133         }
 134
 135         atomic_long_set(&f->f_count, 1);
 136         rwlock_init(&f->f_owner.lock);
 137         spin_lock_init(&f->f_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  * @mnt: the vfsmount on which the file will reside
 154  * @dentry: the dentry representing 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  * Use this instead of get_empty_filp() to get a new
 159  * 'struct file'.  Do so because of the same initialization
 160  * pitfalls reasons listed for init_file().  This is a
 161  * preferred interface to using init_file().
 162  *
 163  * If all the callers of init_file() are eliminated, its
 164  * code should be moved into this function.
 165  */
 166 struct file *alloc_file(struct path *path, fmode_t mode,
 167                 const struct file_operations *fop)
 168 {
 169         struct file *file;
 170
 171         file = get_empty_filp();
 172         if (IS_ERR(file))
 173                 return file;
 174
 175         file->f_path = *path;
 176         file->f_inode = path->dentry->d_inode;
 177         file->f_mapping = path->dentry->d_inode->i_mapping;
 178         file->f_mode = mode;
 179         file->f_op = fop;
 180
 181         /*
 182          * These mounts don't really matter in practice
 183          * for r/o bind mounts.  They aren't userspace-
 184          * visible.  We do this for consistency, and so
 185          * that we can do debugging checks at __fput()
 186          */
 187         if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
 188                 file_take_write(file);
 189                 WARN_ON(mnt_clone_write(path->mnt));
 190         }
 191         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 192                 i_readcount_inc(path->dentry->d_inode);
 193         return file;
 194 }
 195 EXPORT_SYMBOL(alloc_file);
 196
 197 /**
 198  * drop_file_write_access - give up ability to write to a file
 199  * @file: the file to which we will stop writing
 200  *
 201  * This is a central place which will give up the ability
 202  * to write to @file, along with access to write through
 203  * its vfsmount.
 204  */
 205 static void drop_file_write_access(struct file *file)
 206 {
 207         struct vfsmount *mnt = file->f_path.mnt;
 208         struct dentry *dentry = file->f_path.dentry;
 209         struct inode *inode = dentry->d_inode;
 210
 211         if (special_file(inode->i_mode))
 212                 return;
 213
 214         put_write_access(inode);
 215         if (file_check_writeable(file) != 0)
 216                 return;
 217         __mnt_drop_write(mnt);
 218         file_release_write(file);
 219 }
 220
 221 /* the real guts of fput() - releasing the last reference to file
 222  */
 223 static void __fput(struct file *file)
 224 {
 225         struct dentry *dentry = file->f_path.dentry;
 226         struct vfsmount *mnt = file->f_path.mnt;
 227         struct inode *inode = dentry->d_inode;
 228
 229         might_sleep();
 230
 231         fsnotify_close(file);
 232         /*
 233          * The function eventpoll_release() should be the first called
 234          * in the file cleanup chain.
 235          */
 236         eventpoll_release(file);
 237         locks_remove_flock(file);
 238
 239         if (unlikely(file->f_flags & FASYNC)) {
 240                 if (file->f_op && file->f_op->fasync)
 241                         file->f_op->fasync(-1, file, 0);
 242         }
 243         ima_file_free(file);
 244         if (file->f_op && file->f_op->release)
 245                 file->f_op->release(inode, file);
 246         security_file_free(file);
 247         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 248                      !(file->f_mode & FMODE_PATH))) {
 249                 cdev_put(inode->i_cdev);
 250         }
 251         fops_put(file->f_op);
 252         put_pid(file->f_owner.pid);
 253         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 254                 i_readcount_dec(inode);
 255         if (file->f_mode & FMODE_WRITE)
 256                 drop_file_write_access(file);
 257         file->f_path.dentry = NULL;
 258         file->f_path.mnt = NULL;
 259         file->f_inode = NULL;
 260         file_free(file);
 261         dput(dentry);
 262         mntput(mnt);
 263 }
 264
 265 static LLIST_HEAD(delayed_fput_list);
 266 static void delayed_fput(struct work_struct *unused)
 267 {
 268         struct llist_node *node = llist_del_all(&delayed_fput_list);
 269         struct llist_node *next;
 270
 271         for (; node; node = next) {
 272                 next = llist_next(node);
 273                 __fput(llist_entry(node, struct file, f_u.fu_llist));
 274         }
 275 }
 276
 277 static void ____fput(struct callback_head *work)
 278 {
 279         __fput(container_of(work, struct file, f_u.fu_rcuhead));
 280 }
 281
 282 /*
 283  * If kernel thread really needs to have the final fput() it has done
 284  * to complete, call this.  The only user right now is the boot - we
 285  * *do* need to make sure our writes to binaries on initramfs has
 286  * not left us with opened struct file waiting for __fput() - execve()
 287  * won't work without that.  Please, don't add more callers without
 288  * very good reasons; in particular, never call that with locks
 289  * held and never call that from a thread that might need to do
 290  * some work on any kind of umount.
 291  */
 292 void flush_delayed_fput(void)
 293 {
 294         delayed_fput(NULL);
 295 }
 296
 297 static DECLARE_WORK(delayed_fput_work, delayed_fput);
 298
 299 void fput(struct file *file)
 300 {
 301         if (atomic_long_dec_and_test(&file->f_count)) {
 302                 struct task_struct *task = current;
 303
 304                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 305                         init_task_work(&file->f_u.fu_rcuhead, ____fput);
 306                         if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
 307                                 return;
 308                 }
 309
 310                 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
 311                         schedule_work(&delayed_fput_work);
 312         }
 313 }
 314
 315 /*
 316  * synchronous analog of fput(); for kernel threads that might be needed
 317  * in some umount() (and thus can't use flush_delayed_fput() without
 318  * risking deadlocks), need to wait for completion of __fput() and know
 319  * for this specific struct file it won't involve anything that would
 320  * need them.  Use only if you really need it - at the very least,
 321  * don't blindly convert fput() by kernel thread to that.
 322  */
 323 void __fput_sync(struct file *file)
 324 {
 325         if (atomic_long_dec_and_test(&file->f_count)) {
 326                 struct task_struct *task = current;
 327                 BUG_ON(!(task->flags & PF_KTHREAD));
 328                 __fput(file);
 329         }
 330 }
 331
 332 EXPORT_SYMBOL(fput);
 333
 334 void put_filp(struct file *file)
 335 {
 336         if (atomic_long_dec_and_test(&file->f_count)) {
 337                 security_file_free(file);
 338                 file_free(file);
 339         }
 340 }
 341
 342 void __init files_init(unsigned long mempages)
 343 {
 344         unsigned long n;
 345
 346         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 347                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 348
 349         /*
 350          * One file with associated inode and dcache is very roughly 1K.
 351          * Per default don't use more than 10% of our memory for files.
 352          */
 353
 354         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 355         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 356         files_defer_init();
 357         percpu_counter_init(&nr_files, 0);
 358 }