acct.c

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/*
 *  linux/kernel/acct.c
 *
 *  BSD Process Accounting for Linux
 *
 *  Author: Marco van Wieringen <[email protected]>
 *
 *  Some code based on ideas and code from:
 *  Thomas K. Dyas <[email protected]>
 *
 *  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 {
    int         active;
    unsigned long       needcheck;
    struct file     *file;
    struct pid_namespace    *ns;
    struct list_head    list;
};

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

/*
 * 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;
    u64 resume;
    u64 suspend;

    spin_lock(&acct_lock);
    res = acct->active;
    if (!file || time_is_before_jiffies(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;

    do_div(suspend, 100);
    do_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");
        }
    }

    acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
    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;
        acct->active = 0;
        acct->file = NULL;
        acct->ns = NULL;
        list_del(&acct->list);
    }
    if (file) {
        acct->file = file;
        acct->ns = ns;
        acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
        acct->active = 1;
        list_add(&acct->list, &acct_list);
    }
    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(struct filename *pathname)
{
    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 = file_open_name(pathname, 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;
}

SYSCALL_DEFINE1(acct, const char __user *, name)
{
    int error = 0;

    if (!capable(CAP_SYS_PACCT))
        return -EPERM;

    if (name) {
        struct filename *tmp = getname(name);
        if (IS_ERR(tmp))
            return (PTR_ERR(tmp));
        error = acct_on(tmp);
        putname(tmp);
    } else {
        struct bsd_acct_struct *acct;

        acct = task_active_pid_ns(current)->bacct;
        if (acct == NULL)
            return 0;

        spin_lock(&acct_lock);
        acct_file_reopen(acct, NULL, NULL);
        spin_unlock(&acct_lock);
    }

    return error;
}

void acct_auto_close_mnt(struct vfsmount *m)
{
    struct bsd_acct_struct *acct;

    spin_lock(&acct_lock);
restart:
    list_for_each_entry(acct, &acct_list, list)
        if (acct->file && acct->file->f_path.mnt == m) {
            acct_file_reopen(acct, NULL, NULL);
            goto restart;
        }
    spin_unlock(&acct_lock);
}

void acct_auto_close(struct super_block *sb)
{
    struct bsd_acct_struct *acct;

    spin_lock(&acct_lock);
restart:
    list_for_each_entry(acct, &acct_list, list)
        if (acct->file && acct->file->f_path.dentry->d_sb == sb) {
            acct_file_reopen(acct, NULL, NULL);
            goto restart;
        }
    spin_unlock(&acct_lock);
}

void acct_exit_ns(struct pid_namespace *ns)
{
    struct bsd_acct_struct *acct = ns->bacct;

    if (acct == NULL)
        return;

    spin_lock(&acct_lock);
    if (acct->file != NULL)
        acct_file_reopen(acct, NULL, NULL);
    spin_unlock(&acct_lock);

    kfree(acct);
}

/*
 *  encode an unsigned long into a comp_t
 *
 *  This routine has been adopted from the encode_comp_t() function in
 *  the kern_acct.c file of the FreeBSD operating system. The encoding
 *  is a 13-bit fraction with a 3-bit (base 8) exponent.
 */

#define MANTSIZE    13          /* 13 bit mantissa. */
#define EXPSIZE     3           /* Base 8 (3 bit) exponent. */
#define MAXFRACT    ((1 << MANTSIZE) - 1)   /* Maximum fractional value. */

static comp_t encode_comp_t(unsigned long value)
{
    int exp, rnd;

    exp = rnd = 0;
    while (value > MAXFRACT) {
        rnd = value & (1 << (EXPSIZE - 1)); /* Round up? */
        value >>= EXPSIZE;  /* Base 8 exponent == 3 bit shift. */
        exp++;
    }

    /*
     * If we need to round up, do it (and handle overflow correctly).
     */
    if (rnd && (++value > MAXFRACT)) {
        value >>= EXPSIZE;
        exp++;
    }

    /*
     * Clean it up and polish it off.
     */
    exp <<= MANTSIZE;       /* Shift the exponent into place */
    exp += value;           /* and add on the mantissa. */
    return exp;
}

#if ACCT_VERSION==1 || ACCT_VERSION==2
/*
 * encode an u64 into a comp2_t (24 bits)
 *
 * Format: 5 bit base 2 exponent, 20 bits mantissa.
 * The leading bit of the mantissa is not stored, but implied for
 * non-zero exponents.
 * Largest encodable value is 50 bits.
 */

#define MANTSIZE2       20                      /* 20 bit mantissa. */
#define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
#define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
#define MAXEXP2         ((1 <<EXPSIZE2) - 1)    /* Maximum exponent. */

static comp2_t encode_comp2_t(u64 value)
{
    int exp, rnd;

    exp = (value > (MAXFRACT2>>1));
    rnd = 0;
    while (value > MAXFRACT2) {
        rnd = value & 1;
        value >>= 1;
        exp++;
    }

    /*
     * If we need to round up, do it (and handle overflow correctly).
     */
    if (rnd && (++value > MAXFRACT2)) {
        value >>= 1;
        exp++;
    }

    if (exp > MAXEXP2) {
        /* Overflow. Return largest representable number instead. */
        return (1ul << (MANTSIZE2+EXPSIZE2-1)) - 1;
    } else {
        return (value & (MAXFRACT2>>1)) | (exp << (MANTSIZE2-1));
    }
}
#endif

#if ACCT_VERSION==3
/*
 * encode an u64 into a 32 bit IEEE float
 */
static u32 encode_float(u64 value)
{
    unsigned exp = 190;
    unsigned u;

    if (value==0) return 0;
    while ((s64)value > 0){
        value <<= 1;
        exp--;
    }
    u = (u32)(value >> 40) & 0x7fffffu;
    return u | (exp << 23);
}
#endif

/*
 *  Write an accounting entry for an exiting process
 *
 *  The acct_process() call is the workhorse of the process
 *  accounting system. The struct acct is built here and then written
 *  into the accounting file. This function should only be called from
 *  do_exit() or when switching to a different output file.
 */

/*
 *  do_acct_process does all actual work. Caller holds the reference to file.
 */
static void do_acct_process(struct bsd_acct_struct *acct,
        struct pid_namespace *ns, struct file *file)
{
    struct pacct_struct *pacct = &current->signal->pacct;
    acct_t ac;
    mm_segment_t fs;
    unsigned long flim;
    u64 elapsed;
    u64 run_time;
    struct timespec uptime;
    struct tty_struct *tty;
    const struct cred *orig_cred;

    /* Perform file operations on behalf of whoever enabled accounting */
    orig_cred = override_creds(file->f_cred);

    /*
     * First check to see if there is enough free_space to continue
     * the process accounting system.
     */
    if (!check_free_space(acct, file))
        goto out;

    /*
     * Fill the accounting struct with the needed info as recorded
     * by the different kernel functions.
     */
    memset(&ac, 0, sizeof(acct_t));

    ac.ac_version = ACCT_VERSION | ACCT_BYTEORDER;
    strlcpy(ac.ac_comm, current->comm, sizeof(ac.ac_comm));

    /* calculate run_time in nsec*/
    do_posix_clock_monotonic_gettime(&uptime);
    run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec;
    run_time -= (u64)current->group_leader->start_time.tv_sec * NSEC_PER_SEC
               + current->group_leader->start_time.tv_nsec;
    /* convert nsec -> AHZ */
    elapsed = nsec_to_AHZ(run_time);
#if ACCT_VERSION==3
    ac.ac_etime = encode_float(elapsed);
#else
    ac.ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
                           (unsigned long) elapsed : (unsigned long) -1l);
#endif
#if ACCT_VERSION==1 || ACCT_VERSION==2
    {
        /* new enlarged etime field */
        comp2_t etime = encode_comp2_t(elapsed);
        ac.ac_etime_hi = etime >> 16;
        ac.ac_etime_lo = (u16) etime;
    }
#endif
    do_div(elapsed, AHZ);
    ac.ac_btime = get_seconds() - elapsed;
    /* we really need to bite the bullet and change layout */
    ac.ac_uid = from_kuid_munged(file->f_cred->user_ns, orig_cred->uid);
    ac.ac_gid = from_kgid_munged(file->f_cred->user_ns, orig_cred->gid);
#if ACCT_VERSION==2
    ac.ac_ahz = AHZ;
#endif
#if ACCT_VERSION==1 || ACCT_VERSION==2
    /* backward-compatible 16 bit fields */
    ac.ac_uid16 = ac.ac_uid;
    ac.ac_gid16 = ac.ac_gid;
#endif
#if ACCT_VERSION==3
    ac.ac_pid = task_tgid_nr_ns(current, ns);
    rcu_read_lock();
    ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
    rcu_read_unlock();
#endif

    spin_lock_irq(&current->sighand->siglock);
    tty = current->signal->tty; /* Safe as we hold the siglock */
    ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
    ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));
    ac.ac_stime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_stime)));
    ac.ac_flag = pacct->ac_flag;
    ac.ac_mem = encode_comp_t(pacct->ac_mem);
    ac.ac_minflt = encode_comp_t(pacct->ac_minflt);
    ac.ac_majflt = encode_comp_t(pacct->ac_majflt);
    ac.ac_exitcode = pacct->ac_exitcode;
    spin_unlock_irq(&current->sighand->siglock);
    ac.ac_io = encode_comp_t(0 /* current->io_usage */);    /* %% */
    ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
    ac.ac_swaps = encode_comp_t(0);

    /*
     * Kernel segment override to datasegment and write it
     * to the accounting file.
     */
    fs = get_fs();
    set_fs(KERNEL_DS);
    /*
     * Accounting records are not subject to resource limits.
     */
    flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
    current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
    file->f_op->write(file, (char *)&ac,
                   sizeof(acct_t), &file->f_pos);
    current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
    set_fs(fs);
out:
    revert_creds(orig_cred);
}

void acct_collect(long exitcode, int group_dead)
{
    struct pacct_struct *pacct = &current->signal->pacct;
    unsigned long vsize = 0;

    if (group_dead && current->mm) {
        struct vm_area_struct *vma;
        down_read(&current->mm->mmap_sem);
        vma = current->mm->mmap;
        while (vma) {
            vsize += vma->vm_end - vma->vm_start;
            vma = vma->vm_next;
        }
        up_read(&current->mm->mmap_sem);
    }

    spin_lock_irq(&current->sighand->siglock);
    if (group_dead)
        pacct->ac_mem = vsize / 1024;
    if (thread_group_leader(current)) {
        pacct->ac_exitcode = exitcode;
        if (current->flags & PF_FORKNOEXEC)
            pacct->ac_flag |= AFORK;
    }
    if (current->flags & PF_SUPERPRIV)
        pacct->ac_flag |= ASU;
    if (current->flags & PF_DUMPCORE)
        pacct->ac_flag |= ACORE;
    if (current->flags & PF_SIGNALED)
        pacct->ac_flag |= AXSIG;
    pacct->ac_utime += current->utime;
    pacct->ac_stime += current->stime;
    pacct->ac_minflt += current->min_flt;
    pacct->ac_majflt += current->maj_flt;
    spin_unlock_irq(&current->sighand->siglock);
}

static void acct_process_in_ns(struct pid_namespace *ns)
{
    struct file *file = NULL;
    struct bsd_acct_struct *acct;

    acct = ns->bacct;
    /*
     * accelerate the common fastpath:
     */
    if (!acct || !acct->file)
        return;

    spin_lock(&acct_lock);
    file = acct->file;
    if (unlikely(!file)) {
        spin_unlock(&acct_lock);
        return;
    }
    get_file(file);
    spin_unlock(&acct_lock);

    do_acct_process(acct, ns, file);
    fput(file);
}

void acct_process(void)
{
    struct pid_namespace *ns;

    /*
     * This loop is safe lockless, since current is still
     * alive and holds its namespace, which in turn holds
     * its parent.
     */
    for (ns = task_active_pid_ns(current); ns != NULL; ns = ns->parent)
        acct_process_in_ns(ns);
}