root/kernel/acct.c

DEFINITIONS

1. check_free_space
2. acct_put
3. to_acct
4. acct_get
5. acct_pin_kill
6. close_work
7. acct_on
8. SYSCALL_DEFINE1
9. acct_exit_ns
10. encode_comp_t
11. encode_comp2_t
12. encode_float
13. fill_ac
14. do_acct_process
15. acct_collect
16. slow_acct_process
17. acct_process

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