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