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 
73 static 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
79 static 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 };
89 
kernel_acct_sysctls_init(void)90 static __init int kernel_acct_sysctls_init(void)
91 {
92 	register_sysctl_init("kernel", kern_acct_table);
93 	return 0;
94 }
95 late_initcall(kernel_acct_sysctls_init);
96 #endif /* CONFIG_SYSCTL */
97 
98 /*
99  * External references and all of the globals.
100  */
101 
102 struct bsd_acct_struct {
103 	struct fs_pin		pin;
104 	atomic_long_t		count;
105 	struct rcu_head		rcu;
106 	struct mutex		lock;
107 	int			active;
108 	unsigned long		needcheck;
109 	struct file		*file;
110 	struct pid_namespace	*ns;
111 	struct work_struct	work;
112 	struct completion	done;
113 };
114 
115 static void do_acct_process(struct bsd_acct_struct *acct);
116 
117 /*
118  * Check the amount of free space and suspend/resume accordingly.
119  */
check_free_space(struct bsd_acct_struct * acct)120 static int check_free_space(struct bsd_acct_struct *acct)
121 {
122 	struct kstatfs sbuf;
123 
124 	if (time_is_after_jiffies(acct->needcheck))
125 		goto out;
126 
127 	/* May block */
128 	if (vfs_statfs(&acct->file->f_path, &sbuf))
129 		goto out;
130 
131 	if (acct->active) {
132 		u64 suspend = sbuf.f_blocks * SUSPEND;
133 		do_div(suspend, 100);
134 		if (sbuf.f_bavail <= suspend) {
135 			acct->active = 0;
136 			pr_info("Process accounting paused\n");
137 		}
138 	} else {
139 		u64 resume = sbuf.f_blocks * RESUME;
140 		do_div(resume, 100);
141 		if (sbuf.f_bavail >= resume) {
142 			acct->active = 1;
143 			pr_info("Process accounting resumed\n");
144 		}
145 	}
146 
147 	acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
148 out:
149 	return acct->active;
150 }
151 
acct_put(struct bsd_acct_struct * p)152 static void acct_put(struct bsd_acct_struct *p)
153 {
154 	if (atomic_long_dec_and_test(&p->count))
155 		kfree_rcu(p, rcu);
156 }
157 
to_acct(struct fs_pin * p)158 static inline struct bsd_acct_struct *to_acct(struct fs_pin *p)
159 {
160 	return p ? container_of(p, struct bsd_acct_struct, pin) : NULL;
161 }
162 
acct_get(struct pid_namespace * ns)163 static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
164 {
165 	struct bsd_acct_struct *res;
166 again:
167 	smp_rmb();
168 	rcu_read_lock();
169 	res = to_acct(READ_ONCE(ns->bacct));
170 	if (!res) {
171 		rcu_read_unlock();
172 		return NULL;
173 	}
174 	if (!atomic_long_inc_not_zero(&res->count)) {
175 		rcu_read_unlock();
176 		cpu_relax();
177 		goto again;
178 	}
179 	rcu_read_unlock();
180 	mutex_lock(&res->lock);
181 	if (res != to_acct(READ_ONCE(ns->bacct))) {
182 		mutex_unlock(&res->lock);
183 		acct_put(res);
184 		goto again;
185 	}
186 	return res;
187 }
188 
acct_pin_kill(struct fs_pin * pin)189 static void acct_pin_kill(struct fs_pin *pin)
190 {
191 	struct bsd_acct_struct *acct = to_acct(pin);
192 	mutex_lock(&acct->lock);
193 	do_acct_process(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 
close_work(struct work_struct * work)202 static 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 	if (file->f_op->flush)
207 		file->f_op->flush(file, NULL);
208 	__fput_sync(file);
209 	complete(&acct->done);
210 }
211 
acct_on(struct filename * pathname)212 static int acct_on(struct filename *pathname)
213 {
214 	struct file *file;
215 	struct vfsmount *mnt, *internal;
216 	struct pid_namespace *ns = task_active_pid_ns(current);
217 	struct bsd_acct_struct *acct;
218 	struct fs_pin *old;
219 	int err;
220 
221 	acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
222 	if (!acct)
223 		return -ENOMEM;
224 
225 	/* Difference from BSD - they don't do O_APPEND */
226 	file = file_open_name(pathname, O_WRONLY|O_APPEND|O_LARGEFILE, 0);
227 	if (IS_ERR(file)) {
228 		kfree(acct);
229 		return PTR_ERR(file);
230 	}
231 
232 	if (!S_ISREG(file_inode(file)->i_mode)) {
233 		kfree(acct);
234 		filp_close(file, NULL);
235 		return -EACCES;
236 	}
237 
238 	if (!(file->f_mode & FMODE_CAN_WRITE)) {
239 		kfree(acct);
240 		filp_close(file, NULL);
241 		return -EIO;
242 	}
243 	internal = mnt_clone_internal(&file->f_path);
244 	if (IS_ERR(internal)) {
245 		kfree(acct);
246 		filp_close(file, NULL);
247 		return PTR_ERR(internal);
248 	}
249 	err = __mnt_want_write(internal);
250 	if (err) {
251 		mntput(internal);
252 		kfree(acct);
253 		filp_close(file, NULL);
254 		return err;
255 	}
256 	mnt = file->f_path.mnt;
257 	file->f_path.mnt = internal;
258 
259 	atomic_long_set(&acct->count, 1);
260 	init_fs_pin(&acct->pin, acct_pin_kill);
261 	acct->file = file;
262 	acct->needcheck = jiffies;
263 	acct->ns = ns;
264 	mutex_init(&acct->lock);
265 	INIT_WORK(&acct->work, close_work);
266 	init_completion(&acct->done);
267 	mutex_lock_nested(&acct->lock, 1);	/* nobody has seen it yet */
268 	pin_insert(&acct->pin, mnt);
269 
270 	rcu_read_lock();
271 	old = xchg(&ns->bacct, &acct->pin);
272 	mutex_unlock(&acct->lock);
273 	pin_kill(old);
274 	__mnt_drop_write(mnt);
275 	mntput(mnt);
276 	return 0;
277 }
278 
279 static DEFINE_MUTEX(acct_on_mutex);
280 
281 /**
282  * sys_acct - enable/disable process accounting
283  * @name: file name for accounting records or NULL to shutdown accounting
284  *
285  * sys_acct() is the only system call needed to implement process
286  * accounting. It takes the name of the file where accounting records
287  * should be written. If the filename is NULL, accounting will be
288  * shutdown.
289  *
290  * Returns: 0 for success or negative errno values for failure.
291  */
SYSCALL_DEFINE1(acct,const char __user *,name)292 SYSCALL_DEFINE1(acct, const char __user *, name)
293 {
294 	int error = 0;
295 
296 	if (!capable(CAP_SYS_PACCT))
297 		return -EPERM;
298 
299 	if (name) {
300 		struct filename *tmp = getname(name);
301 
302 		if (IS_ERR(tmp))
303 			return PTR_ERR(tmp);
304 		mutex_lock(&acct_on_mutex);
305 		error = acct_on(tmp);
306 		mutex_unlock(&acct_on_mutex);
307 		putname(tmp);
308 	} else {
309 		rcu_read_lock();
310 		pin_kill(task_active_pid_ns(current)->bacct);
311 	}
312 
313 	return error;
314 }
315 
acct_exit_ns(struct pid_namespace * ns)316 void acct_exit_ns(struct pid_namespace *ns)
317 {
318 	rcu_read_lock();
319 	pin_kill(ns->bacct);
320 }
321 
322 /*
323  *  encode an u64 into a comp_t
324  *
325  *  This routine has been adopted from the encode_comp_t() function in
326  *  the kern_acct.c file of the FreeBSD operating system. The encoding
327  *  is a 13-bit fraction with a 3-bit (base 8) exponent.
328  */
329 
330 #define	MANTSIZE	13			/* 13 bit mantissa. */
331 #define	EXPSIZE		3			/* Base 8 (3 bit) exponent. */
332 #define	MAXFRACT	((1 << MANTSIZE) - 1)	/* Maximum fractional value. */
333 
encode_comp_t(u64 value)334 static comp_t encode_comp_t(u64 value)
335 {
336 	int exp, rnd;
337 
338 	exp = rnd = 0;
339 	while (value > MAXFRACT) {
340 		rnd = value & (1 << (EXPSIZE - 1));	/* Round up? */
341 		value >>= EXPSIZE;	/* Base 8 exponent == 3 bit shift. */
342 		exp++;
343 	}
344 
345 	/*
346 	 * If we need to round up, do it (and handle overflow correctly).
347 	 */
348 	if (rnd && (++value > MAXFRACT)) {
349 		value >>= EXPSIZE;
350 		exp++;
351 	}
352 
353 	if (exp > (((comp_t) ~0U) >> MANTSIZE))
354 		return (comp_t) ~0U;
355 	/*
356 	 * Clean it up and polish it off.
357 	 */
358 	exp <<= MANTSIZE;		/* Shift the exponent into place */
359 	exp += value;			/* and add on the mantissa. */
360 	return exp;
361 }
362 
363 #if ACCT_VERSION == 1 || ACCT_VERSION == 2
364 /*
365  * encode an u64 into a comp2_t (24 bits)
366  *
367  * Format: 5 bit base 2 exponent, 20 bits mantissa.
368  * The leading bit of the mantissa is not stored, but implied for
369  * non-zero exponents.
370  * Largest encodable value is 50 bits.
371  */
372 
373 #define MANTSIZE2       20                      /* 20 bit mantissa. */
374 #define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
375 #define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
376 #define MAXEXP2         ((1 << EXPSIZE2) - 1)    /* Maximum exponent. */
377 
encode_comp2_t(u64 value)378 static comp2_t encode_comp2_t(u64 value)
379 {
380 	int exp, rnd;
381 
382 	exp = (value > (MAXFRACT2>>1));
383 	rnd = 0;
384 	while (value > MAXFRACT2) {
385 		rnd = value & 1;
386 		value >>= 1;
387 		exp++;
388 	}
389 
390 	/*
391 	 * If we need to round up, do it (and handle overflow correctly).
392 	 */
393 	if (rnd && (++value > MAXFRACT2)) {
394 		value >>= 1;
395 		exp++;
396 	}
397 
398 	if (exp > MAXEXP2) {
399 		/* Overflow. Return largest representable number instead. */
400 		return (1ul << (MANTSIZE2+EXPSIZE2-1)) - 1;
401 	} else {
402 		return (value & (MAXFRACT2>>1)) | (exp << (MANTSIZE2-1));
403 	}
404 }
405 #elif ACCT_VERSION == 3
406 /*
407  * encode an u64 into a 32 bit IEEE float
408  */
encode_float(u64 value)409 static u32 encode_float(u64 value)
410 {
411 	unsigned exp = 190;
412 	unsigned u;
413 
414 	if (value == 0)
415 		return 0;
416 	while ((s64)value > 0) {
417 		value <<= 1;
418 		exp--;
419 	}
420 	u = (u32)(value >> 40) & 0x7fffffu;
421 	return u | (exp << 23);
422 }
423 #endif
424 
425 /*
426  *  Write an accounting entry for an exiting process
427  *
428  *  The acct_process() call is the workhorse of the process
429  *  accounting system. The struct acct is built here and then written
430  *  into the accounting file. This function should only be called from
431  *  do_exit() or when switching to a different output file.
432  */
433 
fill_ac(acct_t * ac)434 static void fill_ac(acct_t *ac)
435 {
436 	struct pacct_struct *pacct = &current->signal->pacct;
437 	u64 elapsed, run_time;
438 	time64_t btime;
439 	struct tty_struct *tty;
440 
441 	/*
442 	 * Fill the accounting struct with the needed info as recorded
443 	 * by the different kernel functions.
444 	 */
445 	memset(ac, 0, sizeof(acct_t));
446 
447 	ac->ac_version = ACCT_VERSION | ACCT_BYTEORDER;
448 	strscpy(ac->ac_comm, current->comm, sizeof(ac->ac_comm));
449 
450 	/* calculate run_time in nsec*/
451 	run_time = ktime_get_ns();
452 	run_time -= current->group_leader->start_time;
453 	/* convert nsec -> AHZ */
454 	elapsed = nsec_to_AHZ(run_time);
455 #if ACCT_VERSION == 3
456 	ac->ac_etime = encode_float(elapsed);
457 #else
458 	ac->ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
459 				(unsigned long) elapsed : (unsigned long) -1l);
460 #endif
461 #if ACCT_VERSION == 1 || ACCT_VERSION == 2
462 	{
463 		/* new enlarged etime field */
464 		comp2_t etime = encode_comp2_t(elapsed);
465 
466 		ac->ac_etime_hi = etime >> 16;
467 		ac->ac_etime_lo = (u16) etime;
468 	}
469 #endif
470 	do_div(elapsed, AHZ);
471 	btime = ktime_get_real_seconds() - elapsed;
472 	ac->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
473 #if ACCT_VERSION == 2
474 	ac->ac_ahz = AHZ;
475 #endif
476 
477 	spin_lock_irq(&current->sighand->siglock);
478 	tty = current->signal->tty;	/* Safe as we hold the siglock */
479 	ac->ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
480 	ac->ac_utime = encode_comp_t(nsec_to_AHZ(pacct->ac_utime));
481 	ac->ac_stime = encode_comp_t(nsec_to_AHZ(pacct->ac_stime));
482 	ac->ac_flag = pacct->ac_flag;
483 	ac->ac_mem = encode_comp_t(pacct->ac_mem);
484 	ac->ac_minflt = encode_comp_t(pacct->ac_minflt);
485 	ac->ac_majflt = encode_comp_t(pacct->ac_majflt);
486 	ac->ac_exitcode = pacct->ac_exitcode;
487 	spin_unlock_irq(&current->sighand->siglock);
488 }
489 /*
490  *  do_acct_process does all actual work. Caller holds the reference to file.
491  */
do_acct_process(struct bsd_acct_struct * acct)492 static void do_acct_process(struct bsd_acct_struct *acct)
493 {
494 	acct_t ac;
495 	unsigned long flim;
496 	const struct cred *orig_cred;
497 	struct file *file = acct->file;
498 
499 	/*
500 	 * Accounting records are not subject to resource limits.
501 	 */
502 	flim = rlimit(RLIMIT_FSIZE);
503 	current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
504 	/* Perform file operations on behalf of whoever enabled accounting */
505 	orig_cred = override_creds(file->f_cred);
506 
507 	/*
508 	 * First check to see if there is enough free_space to continue
509 	 * the process accounting system.
510 	 */
511 	if (!check_free_space(acct))
512 		goto out;
513 
514 	fill_ac(&ac);
515 	/* we really need to bite the bullet and change layout */
516 	ac.ac_uid = from_kuid_munged(file->f_cred->user_ns, orig_cred->uid);
517 	ac.ac_gid = from_kgid_munged(file->f_cred->user_ns, orig_cred->gid);
518 #if ACCT_VERSION == 1 || ACCT_VERSION == 2
519 	/* backward-compatible 16 bit fields */
520 	ac.ac_uid16 = ac.ac_uid;
521 	ac.ac_gid16 = ac.ac_gid;
522 #elif ACCT_VERSION == 3
523 	{
524 		struct pid_namespace *ns = acct->ns;
525 
526 		ac.ac_pid = task_tgid_nr_ns(current, ns);
527 		rcu_read_lock();
528 		ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent),
529 					     ns);
530 		rcu_read_unlock();
531 	}
532 #endif
533 	/*
534 	 * Get freeze protection. If the fs is frozen, just skip the write
535 	 * as we could deadlock the system otherwise.
536 	 */
537 	if (file_start_write_trylock(file)) {
538 		/* it's been opened O_APPEND, so position is irrelevant */
539 		loff_t pos = 0;
540 		__kernel_write(file, &ac, sizeof(acct_t), &pos);
541 		file_end_write(file);
542 	}
543 out:
544 	current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
545 	revert_creds(orig_cred);
546 }
547 
548 /**
549  * acct_collect - collect accounting information into pacct_struct
550  * @exitcode: task exit code
551  * @group_dead: not 0, if this thread is the last one in the process.
552  */
acct_collect(long exitcode,int group_dead)553 void acct_collect(long exitcode, int group_dead)
554 {
555 	struct pacct_struct *pacct = &current->signal->pacct;
556 	u64 utime, stime;
557 	unsigned long vsize = 0;
558 
559 	if (group_dead && current->mm) {
560 		struct mm_struct *mm = current->mm;
561 		VMA_ITERATOR(vmi, mm, 0);
562 		struct vm_area_struct *vma;
563 
564 		mmap_read_lock(mm);
565 		for_each_vma(vmi, vma)
566 			vsize += vma->vm_end - vma->vm_start;
567 		mmap_read_unlock(mm);
568 	}
569 
570 	spin_lock_irq(&current->sighand->siglock);
571 	if (group_dead)
572 		pacct->ac_mem = vsize / 1024;
573 	if (thread_group_leader(current)) {
574 		pacct->ac_exitcode = exitcode;
575 		if (current->flags & PF_FORKNOEXEC)
576 			pacct->ac_flag |= AFORK;
577 	}
578 	if (current->flags & PF_SUPERPRIV)
579 		pacct->ac_flag |= ASU;
580 	if (current->flags & PF_DUMPCORE)
581 		pacct->ac_flag |= ACORE;
582 	if (current->flags & PF_SIGNALED)
583 		pacct->ac_flag |= AXSIG;
584 
585 	task_cputime(current, &utime, &stime);
586 	pacct->ac_utime += utime;
587 	pacct->ac_stime += stime;
588 	pacct->ac_minflt += current->min_flt;
589 	pacct->ac_majflt += current->maj_flt;
590 	spin_unlock_irq(&current->sighand->siglock);
591 }
592 
slow_acct_process(struct pid_namespace * ns)593 static void slow_acct_process(struct pid_namespace *ns)
594 {
595 	for ( ; ns; ns = ns->parent) {
596 		struct bsd_acct_struct *acct = acct_get(ns);
597 		if (acct) {
598 			do_acct_process(acct);
599 			mutex_unlock(&acct->lock);
600 			acct_put(acct);
601 		}
602 	}
603 }
604 
605 /**
606  * acct_process - handles process accounting for an exiting task
607  */
acct_process(void)608 void acct_process(void)
609 {
610 	struct pid_namespace *ns;
611 
612 	/*
613 	 * This loop is safe lockless, since current is still
614 	 * alive and holds its namespace, which in turn holds
615 	 * its parent.
616 	 */
617 	for (ns = task_active_pid_ns(current); ns != NULL; ns = ns->parent) {
618 		if (ns->bacct)
619 			break;
620 	}
621 	if (unlikely(ns))
622 		slow_acct_process(ns);
623 }
624