acct.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  linux/kernel/acct.c
  4 *
  5 *  BSD Process Accounting for Linux
  6 *
  7 *  Author: Marco van Wieringen <mvw@planets.elm.net>
  8 *
  9 *  Some code based on ideas and code from:
 10 *  Thomas K. Dyas <tdyas@eden.rutgers.edu>
 11 *
 12 *  This file implements BSD-style process accounting. Whenever any
 13 *  process exits, an accounting record of type "struct acct" is
 14 *  written to the file specified with the acct() system call. It is
 15 *  up to user-level programs to do useful things with the accounting
 16 *  log. The kernel just provides the raw accounting information.
 17 *
 18 * (C) Copyright 1995 - 1997 Marco van Wieringen - ELM Consultancy B.V.
 19 *
 20 *  Plugged two leaks. 1) It didn't return acct_file into the free_filps if
 21 *  the file happened to be read-only. 2) If the accounting was suspended
 22 *  due to the lack of space it happily allowed to reopen it and completely
 23 *  lost the old acct_file. 3/10/98, Al Viro.
 24 *
 25 *  Now we silently close acct_file on attempt to reopen. Cleaned sys_acct().
 26 *  XTerms and EMACS are manifestations of pure evil. 21/10/98, AV.
 27 *
 28 *  Fixed a nasty interaction with sys_umount(). If the accounting
 29 *  was suspeneded we failed to stop it on umount(). Messy.
 30 *  Another one: remount to readonly didn't stop accounting.
 31 *	Question: what should we do if we have CAP_SYS_ADMIN but not
 32 *  CAP_SYS_PACCT? Current code does the following: umount returns -EBUSY
 33 *  unless we are messing with the root. In that case we are getting a
 34 *  real mess with do_remount_sb(). 9/11/98, AV.
 35 *
 36 *  Fixed a bunch of races (and pair of leaks). Probably not the best way,
 37 *  but this one obviously doesn't introduce deadlocks. Later. BTW, found
 38 *  one race (and leak) in BSD implementation.
 39 *  OK, that's better. ANOTHER race and leak in BSD variant. There always
 40 *  is one more bug... 10/11/98, AV.
 41 *
 42 *	Oh, fsck... Oopsable SMP race in do_process_acct() - we must hold
 43 * ->mmap_lock to walk the vma list of current->mm. Nasty, since it leaks
 44 * a struct file opened for write. Fixed. 2/6/2000, AV.
 45 */
 46
 47#include <linux/slab.h>
 48#include <linux/acct.h>
 49#include <linux/capability.h>
 50#include <linux/tty.h>
 51#include <linux/statfs.h>
 52#include <linux/jiffies.h>
 53#include <linux/syscalls.h>
 54#include <linux/namei.h>
 55#include <linux/sched/cputime.h>
 56
 57#include <asm/div64.h>
 58#include <linux/pid_namespace.h>
 59#include <linux/fs_pin.h>
 60
 61/*
 62 * These constants control the amount of freespace that suspend and
 63 * resume the process accounting system, and the time delay between
 64 * each check.
 65 * Turned into sysctl-controllable parameters. AV, 12/11/98
 66 */
 67
 68static int acct_parm[3] = {4, 2, 30};
 69#define RESUME		(acct_parm[0])	/* >foo% free space - resume */
 70#define SUSPEND		(acct_parm[1])	/* <foo% free space - suspend */
 71#define ACCT_TIMEOUT	(acct_parm[2])	/* foo second timeout between checks */
 72
 73#ifdef CONFIG_SYSCTL
 74static const struct ctl_table kern_acct_table[] = {
 75	{
 76		.procname       = "acct",
 77		.data           = &acct_parm,
 78		.maxlen         = 3*sizeof(int),
 79		.mode           = 0644,
 80		.proc_handler   = proc_dointvec,
 81	},
 82};
 83
 84static __init int kernel_acct_sysctls_init(void)
 85{
 86	register_sysctl_init("kernel", kern_acct_table);
 87	return 0;
 88}
 89late_initcall(kernel_acct_sysctls_init);
 90#endif /* CONFIG_SYSCTL */
 91
 92/*
 93 * External references and all of the globals.
 94 */
 95
 96struct bsd_acct_struct {
 97	struct fs_pin		pin;
 98	atomic_long_t		count;
 99	struct rcu_head		rcu;
100	struct mutex		lock;
101	bool			active;
102	bool			check_space;
103	unsigned long		needcheck;
104	struct file		*file;
105	struct pid_namespace	*ns;
106	struct work_struct	work;
107	struct completion	done;
108	acct_t			ac;
109};
110
111static void fill_ac(struct bsd_acct_struct *acct);
112static void acct_write_process(struct bsd_acct_struct *acct);
113
114/*
115 * Check the amount of free space and suspend/resume accordingly.
116 */
117static bool check_free_space(struct bsd_acct_struct *acct)
118{
119	struct kstatfs sbuf;
120
121	if (!acct->check_space)
122		return acct->active;
123
124	/* May block */
125	if (vfs_statfs(&acct->file->f_path, &sbuf))
126		return acct->active;
127
128	if (acct->active) {
129		u64 suspend = sbuf.f_blocks * SUSPEND;
130		do_div(suspend, 100);
131		if (sbuf.f_bavail <= suspend) {
132			acct->active = false;
133			pr_info("Process accounting paused\n");
134		}
135	} else {
136		u64 resume = sbuf.f_blocks * RESUME;
137		do_div(resume, 100);
138		if (sbuf.f_bavail >= resume) {
139			acct->active = true;
140			pr_info("Process accounting resumed\n");
141		}
142	}
143
144	acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
145	return acct->active;
146}
147
148static void acct_put(struct bsd_acct_struct *p)
149{
150	if (atomic_long_dec_and_test(&p->count))
151		kfree_rcu(p, rcu);
152}
153
154static inline struct bsd_acct_struct *to_acct(struct fs_pin *p)
155{
156	return p ? container_of(p, struct bsd_acct_struct, pin) : NULL;
157}
158
159static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
160{
161	struct bsd_acct_struct *res;
162again:
163	smp_rmb();
164	rcu_read_lock();
165	res = to_acct(READ_ONCE(ns->bacct));
166	if (!res) {
167		rcu_read_unlock();
168		return NULL;
169	}
170	if (!atomic_long_inc_not_zero(&res->count)) {
171		rcu_read_unlock();
172		cpu_relax();
173		goto again;
174	}
175	rcu_read_unlock();
176	mutex_lock(&res->lock);
177	if (res != to_acct(READ_ONCE(ns->bacct))) {
178		mutex_unlock(&res->lock);
179		acct_put(res);
180		goto again;
181	}
182	return res;
183}
184
185static void acct_pin_kill(struct fs_pin *pin)
186{
187	struct bsd_acct_struct *acct = to_acct(pin);
188	mutex_lock(&acct->lock);
189	/*
190	 * Fill the accounting struct with the exiting task's info
191	 * before punting to the workqueue.
192	 */
193	fill_ac(acct);
194	schedule_work(&acct->work);
195	wait_for_completion(&acct->done);
196	cmpxchg(&acct->ns->bacct, pin, NULL);
197	mutex_unlock(&acct->lock);
198	pin_remove(pin);
199	acct_put(acct);
200}
201
202static void close_work(struct work_struct *work)
203{
204	struct bsd_acct_struct *acct = container_of(work, struct bsd_acct_struct, work);
205	struct file *file = acct->file;
206
207	/* We were fired by acct_pin_kill() which holds acct->lock. */
208	acct_write_process(acct);
209	if (file->f_op->flush)
210		file->f_op->flush(file, NULL);
211	__fput_sync(file);
212	complete(&acct->done);
213}
214
215DEFINE_FREE(fput_sync, struct file *, if (!IS_ERR_OR_NULL(_T)) __fput_sync(_T))
216static int acct_on(const char __user *name)
217{
218	/* Difference from BSD - they don't do O_APPEND */
219	const int open_flags = O_WRONLY|O_APPEND|O_LARGEFILE;
220	struct pid_namespace *ns = task_active_pid_ns(current);
221	struct filename *pathname __free(putname) = getname(name);
222	struct file *original_file __free(fput) = NULL;	// in that order
223	struct path internal __free(path_put) = {};	// in that order
224	struct file *file __free(fput_sync) = NULL;	// in that order
225	struct bsd_acct_struct *acct;
226	struct vfsmount *mnt;
227	struct fs_pin *old;
228
229	if (IS_ERR(pathname))
230		return PTR_ERR(pathname);
231	original_file = file_open_name(pathname, open_flags, 0);
232	if (IS_ERR(original_file))
233		return PTR_ERR(original_file);
234
235	mnt = mnt_clone_internal(&original_file->f_path);
236	if (IS_ERR(mnt))
237		return PTR_ERR(mnt);
238
239	internal.mnt = mnt;
240	internal.dentry = dget(mnt->mnt_root);
241
242	file = dentry_open(&internal, open_flags, current_cred());
243	if (IS_ERR(file))
244		return PTR_ERR(file);
245
246	if (!S_ISREG(file_inode(file)->i_mode))
247		return -EACCES;
248
249	/* Exclude kernel kernel internal filesystems. */
250	if (file_inode(file)->i_sb->s_flags & (SB_NOUSER | SB_KERNMOUNT))
251		return -EINVAL;
252
253	/* Exclude procfs and sysfs. */
254	if (file_inode(file)->i_sb->s_iflags & SB_I_USERNS_VISIBLE)
255		return -EINVAL;
256
257	if (!(file->f_mode & FMODE_CAN_WRITE))
258		return -EIO;
259
260	acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
261	if (!acct)
262		return -ENOMEM;
263
264	atomic_long_set(&acct->count, 1);
265	init_fs_pin(&acct->pin, acct_pin_kill);
266	acct->file = no_free_ptr(file);
267	acct->needcheck = jiffies;
268	acct->ns = ns;
269	mutex_init(&acct->lock);
270	INIT_WORK(&acct->work, close_work);
271	init_completion(&acct->done);
272	mutex_lock_nested(&acct->lock, 1);	/* nobody has seen it yet */
273	pin_insert(&acct->pin, original_file->f_path.mnt);
274
275	rcu_read_lock();
276	old = xchg(&ns->bacct, &acct->pin);
277	mutex_unlock(&acct->lock);
278	pin_kill(old);
279	return 0;
280}
281
282static DEFINE_MUTEX(acct_on_mutex);
283
284/**
285 * sys_acct - enable/disable process accounting
286 * @name: file name for accounting records or NULL to shutdown accounting
287 *
288 * sys_acct() is the only system call needed to implement process
289 * accounting. It takes the name of the file where accounting records
290 * should be written. If the filename is NULL, accounting will be
291 * shutdown.
292 *
293 * Returns: 0 for success or negative errno values for failure.
294 */
295SYSCALL_DEFINE1(acct, const char __user *, name)
296{
297	int error = 0;
298
299	if (!capable(CAP_SYS_PACCT))
300		return -EPERM;
301
302	if (name) {
303		mutex_lock(&acct_on_mutex);
304		error = acct_on(name);
305		mutex_unlock(&acct_on_mutex);
306	} else {
307		rcu_read_lock();
308		pin_kill(task_active_pid_ns(current)->bacct);
309	}
310
311	return error;
312}
313
314void acct_exit_ns(struct pid_namespace *ns)
315{
316	rcu_read_lock();
317	pin_kill(ns->bacct);
318}
319
320/*
321 *  encode an u64 into a comp_t
322 *
323 *  This routine has been adopted from the encode_comp_t() function in
324 *  the kern_acct.c file of the FreeBSD operating system. The encoding
325 *  is a 13-bit fraction with a 3-bit (base 8) exponent.
326 */
327
328#define	MANTSIZE	13			/* 13 bit mantissa. */
329#define	EXPSIZE		3			/* Base 8 (3 bit) exponent. */
330#define	MAXFRACT	((1 << MANTSIZE) - 1)	/* Maximum fractional value. */
331
332static comp_t encode_comp_t(u64 value)
333{
334	int exp, rnd;
335
336	exp = rnd = 0;
337	while (value > MAXFRACT) {
338		rnd = value & (1 << (EXPSIZE - 1));	/* Round up? */
339		value >>= EXPSIZE;	/* Base 8 exponent == 3 bit shift. */
340		exp++;
341	}
342
343	/*
344	 * If we need to round up, do it (and handle overflow correctly).
345	 */
346	if (rnd && (++value > MAXFRACT)) {
347		value >>= EXPSIZE;
348		exp++;
349	}
350
351	if (exp > (((comp_t) ~0U) >> MANTSIZE))
352		return (comp_t) ~0U;
353	/*
354	 * Clean it up and polish it off.
355	 */
356	exp <<= MANTSIZE;		/* Shift the exponent into place */
357	exp += value;			/* and add on the mantissa. */
358	return exp;
359}
360
361#if ACCT_VERSION == 1 || ACCT_VERSION == 2
362/*
363 * encode an u64 into a comp2_t (24 bits)
364 *
365 * Format: 5 bit base 2 exponent, 20 bits mantissa.
366 * The leading bit of the mantissa is not stored, but implied for
367 * non-zero exponents.
368 * Largest encodable value is 50 bits.
369 */
370
371#define MANTSIZE2       20                      /* 20 bit mantissa. */
372#define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
373#define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
374#define MAXEXP2         ((1 << EXPSIZE2) - 1)    /* Maximum exponent. */
375
376static comp2_t encode_comp2_t(u64 value)
377{
378	int exp, rnd;
379
380	exp = (value > (MAXFRACT2>>1));
381	rnd = 0;
382	while (value > MAXFRACT2) {
383		rnd = value & 1;
384		value >>= 1;
385		exp++;
386	}
387
388	/*
389	 * If we need to round up, do it (and handle overflow correctly).
390	 */
391	if (rnd && (++value > MAXFRACT2)) {
392		value >>= 1;
393		exp++;
394	}
395
396	if (exp > MAXEXP2) {
397		/* Overflow. Return largest representable number instead. */
398		return (1ul << (MANTSIZE2+EXPSIZE2-1)) - 1;
399	} else {
400		return (value & (MAXFRACT2>>1)) | (exp << (MANTSIZE2-1));
401	}
402}
403#elif ACCT_VERSION == 3
404/*
405 * encode an u64 into a 32 bit IEEE float
406 */
407static u32 encode_float(u64 value)
408{
409	unsigned exp = 190;
410	unsigned u;
411
412	if (value == 0)
413		return 0;
414	while ((s64)value > 0) {
415		value <<= 1;
416		exp--;
417	}
418	u = (u32)(value >> 40) & 0x7fffffu;
419	return u | (exp << 23);
420}
421#endif
422
423/*
424 *  Write an accounting entry for an exiting process
425 *
426 *  The acct_process() call is the workhorse of the process
427 *  accounting system. The struct acct is built here and then written
428 *  into the accounting file. This function should only be called from
429 *  do_exit() or when switching to a different output file.
430 */
431
432static void fill_ac(struct bsd_acct_struct *acct)
433{
434	struct pacct_struct *pacct = &current->signal->pacct;
435	struct file *file = acct->file;
436	acct_t *ac = &acct->ac;
437	u64 elapsed, run_time;
438	time64_t btime;
439	struct tty_struct *tty;
440
441	lockdep_assert_held(&acct->lock);
442
443	if (time_is_after_jiffies(acct->needcheck)) {
444		acct->check_space = false;
445
446		/* Don't fill in @ac if nothing will be written. */
447		if (!acct->active)
448			return;
449	} else {
450		acct->check_space = true;
451	}
452
453	/*
454	 * Fill the accounting struct with the needed info as recorded
455	 * by the different kernel functions.
456	 */
457	memset(ac, 0, sizeof(acct_t));
458
459	ac->ac_version = ACCT_VERSION | ACCT_BYTEORDER;
460	strscpy(ac->ac_comm, current->comm, sizeof(ac->ac_comm));
461
462	/* calculate run_time in nsec*/
463	run_time = ktime_get_ns();
464	run_time -= current->group_leader->start_time;
465	/* convert nsec -> AHZ */
466	elapsed = nsec_to_AHZ(run_time);
467#if ACCT_VERSION == 3
468	ac->ac_etime = encode_float(elapsed);
469#else
470	ac->ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
471				(unsigned long) elapsed : (unsigned long) -1l);
472#endif
473#if ACCT_VERSION == 1 || ACCT_VERSION == 2
474	{
475		/* new enlarged etime field */
476		comp2_t etime = encode_comp2_t(elapsed);
477
478		ac->ac_etime_hi = etime >> 16;
479		ac->ac_etime_lo = (u16) etime;
480	}
481#endif
482	do_div(elapsed, AHZ);
483	btime = ktime_get_real_seconds() - elapsed;
484	ac->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
485#if ACCT_VERSION == 2
486	ac->ac_ahz = AHZ;
487#endif
488
489	spin_lock_irq(&current->sighand->siglock);
490	tty = current->signal->tty;	/* Safe as we hold the siglock */
491	ac->ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
492	ac->ac_utime = encode_comp_t(nsec_to_AHZ(pacct->ac_utime));
493	ac->ac_stime = encode_comp_t(nsec_to_AHZ(pacct->ac_stime));
494	ac->ac_flag = pacct->ac_flag;
495	ac->ac_mem = encode_comp_t(pacct->ac_mem);
496	ac->ac_minflt = encode_comp_t(pacct->ac_minflt);
497	ac->ac_majflt = encode_comp_t(pacct->ac_majflt);
498	ac->ac_exitcode = pacct->ac_exitcode;
499	spin_unlock_irq(&current->sighand->siglock);
500
501	/* we really need to bite the bullet and change layout */
502	ac->ac_uid = from_kuid_munged(file->f_cred->user_ns, current_uid());
503	ac->ac_gid = from_kgid_munged(file->f_cred->user_ns, current_gid());
504#if ACCT_VERSION == 1 || ACCT_VERSION == 2
505	/* backward-compatible 16 bit fields */
506	ac->ac_uid16 = ac->ac_uid;
507	ac->ac_gid16 = ac->ac_gid;
508#elif ACCT_VERSION == 3
509	{
510		struct pid_namespace *ns = acct->ns;
511
512		ac->ac_pid = task_tgid_nr_ns(current, ns);
513		rcu_read_lock();
514		ac->ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
515		rcu_read_unlock();
516	}
517#endif
518}
519
520static void acct_write_process(struct bsd_acct_struct *acct)
521{
522	struct file *file = acct->file;
523	acct_t *ac = &acct->ac;
524
525	/* Perform file operations on behalf of whoever enabled accounting */
526	scoped_with_creds(file->f_cred) {
527		/*
528		 * First check to see if there is enough free_space to continue
529		 * the process accounting system. Then get freeze protection. If
530		 * the fs is frozen, just skip the write as we could deadlock
531		 * the system otherwise.
532		 */
533		if (check_free_space(acct) && file_start_write_trylock(file)) {
534			/* it's been opened O_APPEND, so position is irrelevant */
535			loff_t pos = 0;
536			__kernel_write(file, ac, sizeof(acct_t), &pos);
537			file_end_write(file);
538		}
539	}
540}
541
542static void do_acct_process(struct bsd_acct_struct *acct)
543{
544	unsigned long flim;
545
546	/* Accounting records are not subject to resource limits. */
547	flim = rlimit(RLIMIT_FSIZE);
548	current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
549	fill_ac(acct);
550	acct_write_process(acct);
551	current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
552}
553
554/**
555 * acct_collect - collect accounting information into pacct_struct
556 * @exitcode: task exit code
557 * @group_dead: not 0, if this thread is the last one in the process.
558 */
559void acct_collect(long exitcode, int group_dead)
560{
561	struct pacct_struct *pacct = &current->signal->pacct;
562	u64 utime, stime;
563	unsigned long vsize = 0;
564
565	if (group_dead && current->mm) {
566		struct mm_struct *mm = current->mm;
567		VMA_ITERATOR(vmi, mm, 0);
568		struct vm_area_struct *vma;
569
570		mmap_read_lock(mm);
571		for_each_vma(vmi, vma)
572			vsize += vma->vm_end - vma->vm_start;
573		mmap_read_unlock(mm);
574	}
575
576	spin_lock_irq(&current->sighand->siglock);
577	if (group_dead)
578		pacct->ac_mem = vsize / 1024;
579	if (thread_group_leader(current)) {
580		pacct->ac_exitcode = exitcode;
581		if (current->flags & PF_FORKNOEXEC)
582			pacct->ac_flag |= AFORK;
583	}
584	if (current->flags & PF_SUPERPRIV)
585		pacct->ac_flag |= ASU;
586	if (current->flags & PF_DUMPCORE)
587		pacct->ac_flag |= ACORE;
588	if (current->flags & PF_SIGNALED)
589		pacct->ac_flag |= AXSIG;
590
591	task_cputime(current, &utime, &stime);
592	pacct->ac_utime += utime;
593	pacct->ac_stime += stime;
594	pacct->ac_minflt += current->min_flt;
595	pacct->ac_majflt += current->maj_flt;
596	spin_unlock_irq(&current->sighand->siglock);
597}
598
599static void slow_acct_process(struct pid_namespace *ns)
600{
601	for ( ; ns; ns = ns->parent) {
602		struct bsd_acct_struct *acct = acct_get(ns);
603		if (acct) {
604			do_acct_process(acct);
605			mutex_unlock(&acct->lock);
606			acct_put(acct);
607		}
608	}
609}
610
611/**
612 * acct_process - handles process accounting for an exiting task
613 */
614void acct_process(void)
615{
616	struct pid_namespace *ns;
617
618	/*
619	 * This loop is safe lockless, since current is still
620	 * alive and holds its namespace, which in turn holds
621	 * its parent.
622	 */
623	for (ns = task_active_pid_ns(current); ns != NULL; ns = ns->parent) {
624		if (ns->bacct)
625			break;
626	}
627	if (unlikely(ns))
628		slow_acct_process(ns);
629}