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/percpu_counter.h>
  24 #include <linux/percpu.h>
  25 #include <linux/hardirq.h>
  26 #include <linux/task_work.h>
  27 #include <linux/ima.h>
  28
  29 #include <linux/atomic.h>
  30
  31 #include "internal.h"
  32
  33 /* sysctl tunables... */
  34 struct files_stat_struct files_stat = {
  35         .max_files = NR_FILE
  36 };
  37
  38 /* SLAB cache for file structures */
  39 static struct kmem_cache *filp_cachep __read_mostly;
  40
  41 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  42
  43 static void file_free_rcu(struct rcu_head *head)
  44 {
  45         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  46
  47         put_cred(f->f_cred);
  48         kmem_cache_free(filp_cachep, f);
  49 }
  50
  51 static inline void file_free(struct file *f)
  52 {
  53         percpu_counter_dec(&nr_files);
  54         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  55 }
  56
  57 /*
  58  * Return the total number of open files in the system
  59  */
  60 static long get_nr_files(void)
  61 {
  62         return percpu_counter_read_positive(&nr_files);
  63 }
  64
  65 /*
  66  * Return the maximum number of open files in the system
  67  */
  68 unsigned long get_max_files(void)
  69 {
  70         return files_stat.max_files;
  71 }
  72 EXPORT_SYMBOL_GPL(get_max_files);
  73
  74 /*
  75  * Handle nr_files sysctl
  76  */
  77 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  78 int proc_nr_files(struct ctl_table *table, int write,
  79                      void __user *buffer, size_t *lenp, loff_t *ppos)
  80 {
  81         files_stat.nr_files = get_nr_files();
  82         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  83 }
  84 #else
  85 int proc_nr_files(struct ctl_table *table, int write,
  86                      void __user *buffer, size_t *lenp, loff_t *ppos)
  87 {
  88         return -ENOSYS;
  89 }
  90 #endif
  91
  92 /* Find an unused file structure and return a pointer to it.
  93  * Returns an error pointer if some error happend e.g. we over file
  94  * structures limit, run out of memory or operation is not permitted.
  95  *
  96  * Be very careful using this.  You are responsible for
  97  * getting write access to any mount that you might assign
  98  * to this filp, if it is opened for write.  If this is not
  99  * done, you will imbalance int the mount's writer count
 100  * and a warning at __fput() time.
 101  */
 102 struct file *get_empty_filp(void)
 103 {
 104         const struct cred *cred = current_cred();
 105         static long old_max;
 106         struct file *f;
 107         int error;
 108
 109         /*
 110          * Privileged users can go above max_files
 111          */
 112         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 113                 /*
 114                  * percpu_counters are inaccurate.  Do an expensive check before
 115                  * we go and fail.
 116                  */
 117                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 118                         goto over;
 119         }
 120
 121         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 122         if (unlikely(!f))
 123                 return ERR_PTR(-ENOMEM);
 124
 125         percpu_counter_inc(&nr_files);
 126         f->f_cred = get_cred(cred);
 127         error = security_file_alloc(f);
 128         if (unlikely(error)) {
 129                 file_free(f);
 130                 return ERR_PTR(error);
 131         }
 132
 133         atomic_long_set(&f->f_count, 1);
 134         rwlock_init(&f->f_owner.lock);
 135         spin_lock_init(&f->f_lock);
 136         mutex_init(&f->f_pos_lock);
 137         eventpoll_init_file(f);
 138         /* f->f_version: 0 */
 139         return f;
 140
 141 over:
 142         /* Ran out of filps - report that */
 143         if (get_nr_files() > old_max) {
 144                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 145                 old_max = get_nr_files();
 146         }
 147         return ERR_PTR(-ENFILE);
 148 }
 149
 150 /**
 151  * alloc_file - allocate and initialize a 'struct file'
 152  *
 153  * @path: the (dentry, vfsmount) pair for the new file
 154  * @mode: the mode with which the new file will be opened
 155  * @fop: the 'struct file_operations' for the new file
 156  */
 157 struct file *alloc_file(struct path *path, fmode_t mode,
 158                 const struct file_operations *fop)
 159 {
 160         struct file *file;
 161
 162         file = get_empty_filp();
 163         if (IS_ERR(file))
 164                 return file;
 165
 166         file->f_path = *path;
 167         file->f_inode = path->dentry->d_inode;
 168         file->f_mapping = path->dentry->d_inode->i_mapping;
 169         if ((mode & FMODE_READ) &&
 170              likely(fop->read || fop->read_iter))
 171                 mode |= FMODE_CAN_READ;
 172         if ((mode & FMODE_WRITE) &&
 173              likely(fop->write || fop->write_iter))
 174                 mode |= FMODE_CAN_WRITE;
 175         file->f_mode = mode;
 176         file->f_op = fop;
 177         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 178                 i_readcount_inc(path->dentry->d_inode);
 179         return file;
 180 }
 181 EXPORT_SYMBOL(alloc_file);
 182
 183 /* the real guts of fput() - releasing the last reference to file
 184  */
 185 static void __fput(struct file *file)
 186 {
 187         struct dentry *dentry = file->f_path.dentry;
 188         struct vfsmount *mnt = file->f_path.mnt;
 189         struct inode *inode = file->f_inode;
 190
 191         might_sleep();
 192
 193         fsnotify_close(file);
 194         /*
 195          * The function eventpoll_release() should be the first called
 196          * in the file cleanup chain.
 197          */
 198         eventpoll_release(file);
 199         locks_remove_file(file);
 200
 201         if (unlikely(file->f_flags & FASYNC)) {
 202                 if (file->f_op->fasync)
 203                         file->f_op->fasync(-1, file, 0);
 204         }
 205         ima_file_free(file);
 206         if (file->f_op->release)
 207                 file->f_op->release(inode, file);
 208         security_file_free(file);
 209         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 210                      !(file->f_mode & FMODE_PATH))) {
 211                 cdev_put(inode->i_cdev);
 212         }
 213         fops_put(file->f_op);
 214         put_pid(file->f_owner.pid);
 215         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 216                 i_readcount_dec(inode);
 217         if (file->f_mode & FMODE_WRITER) {
 218                 put_write_access(inode);
 219                 __mnt_drop_write(mnt);
 220         }
 221         file->f_path.dentry = NULL;
 222         file->f_path.mnt = NULL;
 223         file->f_inode = NULL;
 224         file_free(file);
 225         dput(dentry);
 226         mntput(mnt);
 227 }
 228
 229 static LLIST_HEAD(delayed_fput_list);
 230 static void delayed_fput(struct work_struct *unused)
 231 {
 232         struct llist_node *node = llist_del_all(&delayed_fput_list);
 233         struct llist_node *next;
 234
 235         for (; node; node = next) {
 236                 next = llist_next(node);
 237                 __fput(llist_entry(node, struct file, f_u.fu_llist));
 238         }
 239 }
 240
 241 static void ____fput(struct callback_head *work)
 242 {
 243         __fput(container_of(work, struct file, f_u.fu_rcuhead));
 244 }
 245
 246 /*
 247  * If kernel thread really needs to have the final fput() it has done
 248  * to complete, call this.  The only user right now is the boot - we
 249  * *do* need to make sure our writes to binaries on initramfs has
 250  * not left us with opened struct file waiting for __fput() - execve()
 251  * won't work without that.  Please, don't add more callers without
 252  * very good reasons; in particular, never call that with locks
 253  * held and never call that from a thread that might need to do
 254  * some work on any kind of umount.
 255  */
 256 void flush_delayed_fput(void)
 257 {
 258         delayed_fput(NULL);
 259 }
 260
 261 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 262
 263 void fput(struct file *file)
 264 {
 265         if (atomic_long_dec_and_test(&file->f_count)) {
 266                 struct task_struct *task = current;
 267
 268                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 269                         init_task_work(&file->f_u.fu_rcuhead, ____fput);
 270                         if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
 271                                 return;
 272                         /*
 273                          * After this task has run exit_task_work(),
 274                          * task_work_add() will fail.  Fall through to delayed
 275                          * fput to avoid leaking *file.
 276                          */
 277                 }
 278
 279                 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
 280                         schedule_delayed_work(&delayed_fput_work, 1);
 281         }
 282 }
 283
 284 /*
 285  * synchronous analog of fput(); for kernel threads that might be needed
 286  * in some umount() (and thus can't use flush_delayed_fput() without
 287  * risking deadlocks), need to wait for completion of __fput() and know
 288  * for this specific struct file it won't involve anything that would
 289  * need them.  Use only if you really need it - at the very least,
 290  * don't blindly convert fput() by kernel thread to that.
 291  */
 292 void __fput_sync(struct file *file)
 293 {
 294         if (atomic_long_dec_and_test(&file->f_count)) {
 295                 struct task_struct *task = current;
 296                 BUG_ON(!(task->flags & PF_KTHREAD));
 297                 __fput(file);
 298         }
 299 }
 300
 301 EXPORT_SYMBOL(fput);
 302
 303 void put_filp(struct file *file)
 304 {
 305         if (atomic_long_dec_and_test(&file->f_count)) {
 306                 security_file_free(file);
 307                 file_free(file);
 308         }
 309 }
 310
 311 void __init files_init(unsigned long mempages)
 312 {
 313         unsigned long n;
 314
 315         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 316                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 317
 318         /*
 319          * One file with associated inode and dcache is very roughly 1K.
 320          * Per default don't use more than 10% of our memory for files.
 321          */
 322
 323         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 324         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 325         percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 326 }