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https://github.com/torvalds/linux.git
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89068c576b
Hooks: Just Say No. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
432 lines
10 KiB
C
432 lines
10 KiB
C
/*
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* linux/fs/file_table.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
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*/
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/security.h>
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#include <linux/eventpoll.h>
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#include <linux/rcupdate.h>
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#include <linux/mount.h>
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#include <linux/capability.h>
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#include <linux/cdev.h>
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#include <linux/fsnotify.h>
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#include <linux/sysctl.h>
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#include <linux/percpu_counter.h>
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#include <linux/ima.h>
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#include <asm/atomic.h>
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#include "internal.h"
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/* sysctl tunables... */
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struct files_stat_struct files_stat = {
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.max_files = NR_FILE
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};
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/* public. Not pretty! */
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__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
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/* SLAB cache for file structures */
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static struct kmem_cache *filp_cachep __read_mostly;
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static struct percpu_counter nr_files __cacheline_aligned_in_smp;
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static inline void file_free_rcu(struct rcu_head *head)
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{
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struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
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put_cred(f->f_cred);
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kmem_cache_free(filp_cachep, f);
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}
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static inline void file_free(struct file *f)
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{
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percpu_counter_dec(&nr_files);
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file_check_state(f);
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call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
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}
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/*
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* Return the total number of open files in the system
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*/
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static int get_nr_files(void)
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{
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return percpu_counter_read_positive(&nr_files);
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}
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/*
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* Return the maximum number of open files in the system
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*/
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int get_max_files(void)
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{
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return files_stat.max_files;
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}
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EXPORT_SYMBOL_GPL(get_max_files);
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/*
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* Handle nr_files sysctl
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*/
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#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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files_stat.nr_files = get_nr_files();
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return proc_dointvec(table, write, buffer, lenp, ppos);
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}
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#else
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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return -ENOSYS;
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}
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#endif
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/* Find an unused file structure and return a pointer to it.
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* Returns NULL, if there are no more free file structures or
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* we run out of memory.
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*
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* Be very careful using this. You are responsible for
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* getting write access to any mount that you might assign
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* to this filp, if it is opened for write. If this is not
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* done, you will imbalance int the mount's writer count
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* and a warning at __fput() time.
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*/
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struct file *get_empty_filp(void)
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{
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const struct cred *cred = current_cred();
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static int old_max;
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struct file * f;
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/*
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* Privileged users can go above max_files
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*/
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if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
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/*
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* percpu_counters are inaccurate. Do an expensive check before
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* we go and fail.
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*/
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if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
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goto over;
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}
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f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
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if (f == NULL)
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goto fail;
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percpu_counter_inc(&nr_files);
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if (security_file_alloc(f))
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goto fail_sec;
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INIT_LIST_HEAD(&f->f_u.fu_list);
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atomic_long_set(&f->f_count, 1);
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rwlock_init(&f->f_owner.lock);
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f->f_cred = get_cred(cred);
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spin_lock_init(&f->f_lock);
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eventpoll_init_file(f);
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/* f->f_version: 0 */
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return f;
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over:
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/* Ran out of filps - report that */
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if (get_nr_files() > old_max) {
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printk(KERN_INFO "VFS: file-max limit %d reached\n",
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get_max_files());
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old_max = get_nr_files();
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}
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goto fail;
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fail_sec:
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file_free(f);
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fail:
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return NULL;
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}
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/**
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* alloc_file - allocate and initialize a 'struct file'
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* @mnt: the vfsmount on which the file will reside
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* @dentry: the dentry representing the new file
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* @mode: the mode with which the new file will be opened
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* @fop: the 'struct file_operations' for the new file
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*
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* Use this instead of get_empty_filp() to get a new
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* 'struct file'. Do so because of the same initialization
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* pitfalls reasons listed for init_file(). This is a
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* preferred interface to using init_file().
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*
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* If all the callers of init_file() are eliminated, its
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* code should be moved into this function.
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*/
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struct file *alloc_file(struct path *path, fmode_t mode,
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const struct file_operations *fop)
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{
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struct file *file;
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file = get_empty_filp();
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if (!file)
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return NULL;
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file->f_path = *path;
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file->f_mapping = path->dentry->d_inode->i_mapping;
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file->f_mode = mode;
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file->f_op = fop;
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/*
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* These mounts don't really matter in practice
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* for r/o bind mounts. They aren't userspace-
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* visible. We do this for consistency, and so
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* that we can do debugging checks at __fput()
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*/
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if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
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file_take_write(file);
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WARN_ON(mnt_clone_write(path->mnt));
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}
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ima_counts_get(file);
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return file;
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}
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EXPORT_SYMBOL(alloc_file);
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void fput(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count))
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__fput(file);
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}
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EXPORT_SYMBOL(fput);
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/**
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* drop_file_write_access - give up ability to write to a file
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* @file: the file to which we will stop writing
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*
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* This is a central place which will give up the ability
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* to write to @file, along with access to write through
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* its vfsmount.
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*/
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void drop_file_write_access(struct file *file)
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{
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struct vfsmount *mnt = file->f_path.mnt;
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struct dentry *dentry = file->f_path.dentry;
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struct inode *inode = dentry->d_inode;
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put_write_access(inode);
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if (special_file(inode->i_mode))
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return;
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if (file_check_writeable(file) != 0)
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return;
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mnt_drop_write(mnt);
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file_release_write(file);
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}
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EXPORT_SYMBOL_GPL(drop_file_write_access);
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/* __fput is called from task context when aio completion releases the last
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* last use of a struct file *. Do not use otherwise.
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*/
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void __fput(struct file *file)
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{
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struct dentry *dentry = file->f_path.dentry;
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struct vfsmount *mnt = file->f_path.mnt;
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struct inode *inode = dentry->d_inode;
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might_sleep();
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fsnotify_close(file);
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/*
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* The function eventpoll_release() should be the first called
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* in the file cleanup chain.
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*/
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eventpoll_release(file);
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locks_remove_flock(file);
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if (unlikely(file->f_flags & FASYNC)) {
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if (file->f_op && file->f_op->fasync)
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file->f_op->fasync(-1, file, 0);
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}
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if (file->f_op && file->f_op->release)
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file->f_op->release(inode, file);
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security_file_free(file);
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ima_file_free(file);
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if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
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cdev_put(inode->i_cdev);
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fops_put(file->f_op);
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put_pid(file->f_owner.pid);
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file_kill(file);
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if (file->f_mode & FMODE_WRITE)
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drop_file_write_access(file);
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file->f_path.dentry = NULL;
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file->f_path.mnt = NULL;
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file_free(file);
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dput(dentry);
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mntput(mnt);
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}
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struct file *fget(unsigned int fd)
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{
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struct file *file;
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struct files_struct *files = current->files;
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rcu_read_lock();
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file = fcheck_files(files, fd);
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if (file) {
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if (!atomic_long_inc_not_zero(&file->f_count)) {
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/* File object ref couldn't be taken */
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rcu_read_unlock();
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return NULL;
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}
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}
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rcu_read_unlock();
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return file;
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}
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EXPORT_SYMBOL(fget);
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/*
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* Lightweight file lookup - no refcnt increment if fd table isn't shared.
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* You can use this only if it is guranteed that the current task already
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* holds a refcnt to that file. That check has to be done at fget() only
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* and a flag is returned to be passed to the corresponding fput_light().
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* There must not be a cloning between an fget_light/fput_light pair.
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*/
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struct file *fget_light(unsigned int fd, int *fput_needed)
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{
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struct file *file;
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struct files_struct *files = current->files;
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*fput_needed = 0;
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if (likely((atomic_read(&files->count) == 1))) {
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file = fcheck_files(files, fd);
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} else {
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rcu_read_lock();
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file = fcheck_files(files, fd);
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if (file) {
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if (atomic_long_inc_not_zero(&file->f_count))
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*fput_needed = 1;
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else
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/* Didn't get the reference, someone's freed */
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file = NULL;
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}
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rcu_read_unlock();
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}
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return file;
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}
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void put_filp(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count)) {
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security_file_free(file);
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file_kill(file);
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file_free(file);
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}
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}
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void file_move(struct file *file, struct list_head *list)
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{
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if (!list)
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return;
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file_list_lock();
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list_move(&file->f_u.fu_list, list);
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file_list_unlock();
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}
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void file_kill(struct file *file)
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{
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if (!list_empty(&file->f_u.fu_list)) {
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file_list_lock();
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list_del_init(&file->f_u.fu_list);
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file_list_unlock();
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}
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}
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int fs_may_remount_ro(struct super_block *sb)
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{
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struct file *file;
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/* Check that no files are currently opened for writing. */
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file_list_lock();
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list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
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struct inode *inode = file->f_path.dentry->d_inode;
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/* File with pending delete? */
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if (inode->i_nlink == 0)
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goto too_bad;
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/* Writeable file? */
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if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
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goto too_bad;
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}
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file_list_unlock();
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return 1; /* Tis' cool bro. */
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too_bad:
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file_list_unlock();
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return 0;
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}
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/**
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* mark_files_ro - mark all files read-only
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* @sb: superblock in question
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*
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* All files are marked read-only. We don't care about pending
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* delete files so this should be used in 'force' mode only.
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*/
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void mark_files_ro(struct super_block *sb)
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{
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struct file *f;
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retry:
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file_list_lock();
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list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
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struct vfsmount *mnt;
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if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
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continue;
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if (!file_count(f))
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continue;
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if (!(f->f_mode & FMODE_WRITE))
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continue;
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f->f_mode &= ~FMODE_WRITE;
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if (file_check_writeable(f) != 0)
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continue;
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file_release_write(f);
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mnt = mntget(f->f_path.mnt);
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file_list_unlock();
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/*
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* This can sleep, so we can't hold
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* the file_list_lock() spinlock.
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*/
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mnt_drop_write(mnt);
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mntput(mnt);
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goto retry;
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}
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file_list_unlock();
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}
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void __init files_init(unsigned long mempages)
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{
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int n;
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filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
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SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
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/*
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* One file with associated inode and dcache is very roughly 1K.
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* Per default don't use more than 10% of our memory for files.
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*/
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n = (mempages * (PAGE_SIZE / 1024)) / 10;
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files_stat.max_files = n;
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if (files_stat.max_files < NR_FILE)
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files_stat.max_files = NR_FILE;
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files_defer_init();
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percpu_counter_init(&nr_files, 0);
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}
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