kernel/acct.c



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/*
 *  linux/kernel/acct.c
 *
 *  BSD Process Accounting for Linux
 *
 *  Author: Marco van Wieringen <mvw@planets.elm.net>
 *
 *  Some code based on ideas and code from:
 *  Thomas K. Dyas <tdyas@eden.rutgers.edu>
 *
 *  This file implements BSD-style process accounting. Whenever any
 *  process exits, an accounting record of type "struct acct" is
 *  written to the file specified with the acct() system call. It is
 *  up to user-level programs to do useful things with the accounting
 *  log. The kernel just provides the raw accounting information.
 *
 * (C) Copyright 1995 - 1997 Marco van Wieringen - ELM Consultancy B.V.
 *
 *  Plugged two leaks. 1) It didn't return acct_file into the free_filps if
 *  the file happened to be read-only. 2) If the accounting was suspended
 *  due to the lack of space it happily allowed to reopen it and completely
 *  lost the old acct_file. 3/10/98, Al Viro.
 *
 *  Now we silently close acct_file on attempt to reopen. Cleaned sys_acct().
 *  XTerms and EMACS are manifestations of pure evil. 21/10/98, AV.
 *
 *  Fixed a nasty interaction with with sys_umount(). If the accointing
 *  was suspeneded we failed to stop it on umount(). Messy.
 *  Another one: remount to readonly didn't stop accounting.
 *	Question: what should we do if we have CAP_SYS_ADMIN but not
 *  CAP_SYS_PACCT? Current code does the following: umount returns -EBUSY
 *  unless we are messing with the root. In that case we are getting a
 *  real mess with do_remount_sb(). 9/11/98, AV.
 *
 *  Fixed a bunch of races (and pair of leaks). Probably not the best way,
 *  but this one obviously doesn't introduce deadlocks. Later. BTW, found
 *  one race (and leak) in BSD implementation.
 *  OK, that's better. ANOTHER race and leak in BSD variant. There always
 *  is one more bug... 10/11/98, AV.
 *
 *	Oh, fsck... Oopsable SMP race in do_process_acct() - we must hold
 * ->mmap_sem to walk the vma list of current->mm. Nasty, since it leaks
 * a struct file opened for write. Fixed. 2/6/2000, AV.
 */

#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/acct.h>
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/tty.h>
#include <linux/security.h>
#include <linux/vfs.h>
#include <linux/jiffies.h>
#include <linux/times.h>
#include <linux/syscalls.h>
#include <linux/mount.h>
#include <asm/uaccess.h>
#include <asm/div64.h>
#include <linux/blkdev.h> /* sector_div */
#include <linux/pid_namespace.h>

/*
 * These constants control the amount of freespace that suspend and
 * resume the process accounting system, and the time delay between
 * each check.
 * Turned into sysctl-controllable parameters. AV, 12/11/98
 */

int acct_parm[3] = {4, 2, 30};
#define RESUME		(acct_parm[0])	/* >foo% free space - resume */
#define SUSPEND		(acct_parm[1])	/* <foo% free space - suspend */
#define ACCT_TIMEOUT	(acct_parm[2])	/* foo second timeout between checks */

/*
 * External references and all of the globals.
 */
static void do_acct_process(struct bsd_acct_struct *acct,
		struct pid_namespace *ns, struct file *);

/*
 * This structure is used so that all the data protected by lock
 * can be placed in the same cache line as the lock.  This primes
 * the cache line to have the data after getting the lock.
 */
struct bsd_acct_struct {
	volatile int		active;
	volatile int		needcheck;
	struct file		*file;
	struct pid_namespace	*ns;
	struct timer_list	timer;
	struct list_head	list;
};

static DEFINE_SPINLOCK(acct_lock);
static LIST_HEAD(acct_list);

/*
 * Called whenever the timer says to check the free space.
 */
static void acct_timeout(unsigned long x)
{
	struct bsd_acct_struct *acct = (struct bsd_acct_struct *)x;
	acct->needcheck = 1;
}

/*
 * Check the amount of free space and suspend/resume accordingly.
 */
static int check_free_space(struct bsd_acct_struct *acct, struct file *file)
{
	struct kstatfs sbuf;
	int res;
	int act;
	sector_t resume;
	sector_t suspend;

	spin_lock(&acct_lock);
	res = acct->active;
	if (!file || !acct->needcheck)
		goto out;
	spin_unlock(&acct_lock);

	/* May block */
	if (vfs_statfs(&file->f_path, &sbuf))
		return res;
	suspend = sbuf.f_blocks * SUSPEND;
	resume = sbuf.f_blocks * RESUME;

	sector_div(suspend, 100);
	sector_div(resume, 100);

	if (sbuf.f_bavail <= suspend)
		act = -1;
	else if (sbuf.f_bavail >= resume)
		act = 1;
	else
		act = 0;

	/*
	 * If some joker switched acct->file under us we'ld better be
	 * silent and _not_ touch anything.
	 */
	spin_lock(&acct_lock);
	if (file != acct->file) {
		if (act)
			res = act>0;
		goto out;
	}

	if (acct->active) {
		if (act < 0) {
			acct->active = 0;
			printk(KERN_INFO "Process accounting paused\n");
		}
	} else {
		if (act > 0) {
			acct->active = 1;
			printk(KERN_INFO "Process accounting resumed\n");
		}
	}

	del_timer(&acct->timer);
	acct->needcheck = 0;
	acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
	add_timer(&acct->timer);
	res = acct->active;
out:
	spin_unlock(&acct_lock);
	return res;
}

/*
 * Close the old accounting file (if currently open) and then replace
 * it with file (if non-NULL).
 *
 * NOTE: acct_lock MUST be held on entry and exit.
 */
static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file,
		struct pid_namespace *ns)
{
	struct file *old_acct = NULL;
	struct pid_namespace *old_ns = NULL;

	if (acct->file) {
		old_acct = acct->file;
		old_ns = acct->ns;
		del_timer(&acct->timer);
		acct->active = 0;
		acct->needcheck = 0;
		acct->file = NULL;
		acct->ns = NULL;
		list_del(&acct->list);
	}
	if (file) {
		acct->file = file;
		acct->ns = ns;
		acct->needcheck = 0;
		acct->active = 1;
		list_add(&acct->list, &acct_list);
		/* It's been deleted if it was used before so this is safe */
		setup_timer(&acct->timer, acct_timeout, (unsigned long)acct);
		acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
		add_timer(&acct->timer);
	}
	if (old_acct) {
		mnt_unpin(old_acct->f_path.mnt);
		spin_unlock(&acct_lock);
		do_acct_process(acct, old_ns, old_acct);
		filp_close(old_acct, NULL);
		spin_lock(&acct_lock);
	}
}

static int acct_on(char *name)
{
	struct file *file;
	struct vfsmount *mnt;
	struct pid_namespace *ns;
	struct bsd_acct_struct *acct = NULL;

	/* Difference from BSD - they don't do O_APPEND */
	file = filp_open(name, O_WRONLY|O_APPEND|O_LARGEFILE, 0);
	if (IS_ERR(file))
		return PTR_ERR(file);

	if (!S_ISREG(file->f_path.dentry->d_inode->i_mode)) {
		filp_close(file, NULL);
		return -EACCES;
	}

	if (!file->f_op->write) {
		filp_close(file, NULL);
		return -EIO;
	}

	ns = task_active_pid_ns(current);
	if (ns->bacct == NULL) {
		acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
		if (acct == NULL) {
			filp_close(file, NULL);
			return -ENOMEM;
		}
	}

	spin_lock(&acct_lock);
	if (ns->bacct == NULL) {
		ns->bacct = acct;
		acct = NULL;
	}

	mnt = file->f_path.mnt;
	mnt_pin(mnt);
	acct_file_reopen(ns->bacct, file, ns);
	spin_unlock(&acct_lock);

	mntput(mnt); /* it's pinned, now give up active reference */
	kfree(acct);

	return 0;
}

/**
 * sys_acct - enable/disable process accounting
 * @name: file name for accounting records or NULL to shutdown accounting
 *
 * Returns 0 for success or negative errno values for failure.
 *
 * sys_acct() is the only system call needed to implement process
 * accounting. It takes the name of the file where accounting records
 * should be written. If the filename is NULL, accounting will be
 * shutdown.
 */
SYSCALL_DEFINE1(acct, const char __user *, name)
{