userns: prevent speculative execution

[mirror_ubuntu-artful-kernel.git] / kernel / acct.c

/*
 *  linux/kernel/acct.c
 *
 *  BSD Process Accounting for Linux
 *
 *  Author: Marco van Wieringen <mvw@planets.elm.net>
 *
 *  Some code based on ideas and code from:
 *  Thomas K. Dyas <tdyas@eden.rutgers.edu>
 *
 *  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 <linux/uaccess.h>
#include <linux/sched/cputime.h>

#include <asm/div64.h>
#include <linux/blkdev.h> /* sector_div */
#include <linux/pid_namespace.h>
#include <linux/fs_pin.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.
 */

struct bsd_acct_struct {
        struct fs_pin           pin;
        atomic_long_t           count;
        struct rcu_head         rcu;
        struct mutex            lock;
        int                     active;
        unsigned long           needcheck;
        struct file             *file;
        struct pid_namespace    *ns;
        struct work_struct      work;
        struct completion       done;
};

static void do_acct_process(struct bsd_acct_struct *acct);

/*
 * Check the amount of free space and suspend/resume accordingly.
 */
static int check_free_space(struct bsd_acct_struct *acct)
{
        struct kstatfs sbuf;

        if (time_is_before_jiffies(acct->needcheck))
                goto out;

        /* May block */
        if (vfs_statfs(&acct->file->f_path, &sbuf))
                goto out;

        if (acct->active) {
                u64 suspend = sbuf.f_blocks * SUSPEND;
                do_div(suspend, 100);
                if (sbuf.f_bavail <= suspend) {
                        acct->active = 0;
                        pr_info("Process accounting paused\n");
                }
        } else {
                u64 resume = sbuf.f_blocks * RESUME;
                do_div(resume, 100);
                if (sbuf.f_bavail >= resume) {
                        acct->active = 1;
                        pr_info("Process accounting resumed\n");
                }
        }

        acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
out:
        return acct->active;
}

static void acct_put(struct bsd_acct_struct *p)
{
        if (atomic_long_dec_and_test(&p->count))
                kfree_rcu(p, rcu);
}

static inline struct bsd_acct_struct *to_acct(struct fs_pin *p)
{
        return p ? container_of(p, struct bsd_acct_struct, pin) : NULL;
}

static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
{
        struct bsd_acct_struct *res;
again:
        smp_rmb();
        rcu_read_lock();
        res = to_acct(ACCESS_ONCE(ns->bacct));
        if (!res) {
                rcu_read_unlock();
                return NULL;
        }
        if (!atomic_long_inc_not_zero(&res->count)) {
                rcu_read_unlock();
                cpu_relax();
                goto again;
        }
        rcu_read_unlock();
        mutex_lock(&res->lock);
        if (res != to_acct(ACCESS_ONCE(ns->bacct))) {
                mutex_unlock(&res->lock);
                acct_put(res);
                goto again;
        }
        return res;
}

static void acct_pin_kill(struct fs_pin *pin)
{
        struct bsd_acct_struct *acct = to_acct(pin);
        mutex_lock(&acct->lock);
        do_acct_process(acct);
        schedule_work(&acct->work);
        wait_for_completion(&acct->done);
        cmpxchg(&acct->ns->bacct, pin, NULL);
        mutex_unlock(&acct->lock);
        pin_remove(pin);
        acct_put(acct);
}

static void close_work(struct work_struct *work)
{
        struct bsd_acct_struct *acct = container_of(work, struct bsd_acct_struct, work);
        struct file *file = acct->file;
        if (file->f_op->flush)
                file->f_op->flush(file, NULL);
        __fput_sync(file);
        complete(&acct->done);
}

static int acct_on(struct filename *pathname)
{
        struct file *file;
        struct vfsmount *mnt, *internal;
        struct pid_namespace *ns = task_active_pid_ns(current);
        struct bsd_acct_struct *acct;
        struct fs_pin *old;
        int err;

        acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
        if (!acct)
                return -ENOMEM;

        /* 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)) {
                kfree(acct);
                return PTR_ERR(file);
        }

        if (!S_ISREG(file_inode(file)->i_mode)) {
                kfree(acct);
                filp_close(file, NULL);
                return -EACCES;
        }

        if (!(file->f_mode & FMODE_CAN_WRITE)) {
                kfree(acct);
                filp_close(file, NULL);
                return -EIO;
        }
        internal = mnt_clone_internal(&file->f_path);
        if (IS_ERR(internal)) {
                kfree(acct);
                filp_close(file, NULL);
                return PTR_ERR(internal);
        }
        err = mnt_want_write(internal);
        if (err) {
                mntput(internal);
                kfree(acct);
                filp_close(file, NULL);
                return err;
        }
        mnt = file->f_path.mnt;
        file->f_path.mnt = internal;

        atomic_long_set(&acct->count, 1);
        init_fs_pin(&acct->pin, acct_pin_kill);
        acct->file = file;
        acct->needcheck = jiffies;
        acct->ns = ns;
        mutex_init(&acct->lock);
        INIT_WORK(&acct->work, close_work);
        init_completion(&acct->done);
        mutex_lock_nested(&acct->lock, 1);      /* nobody has seen it yet */
        pin_insert(&acct->pin, mnt);

        rcu_read_lock();
        old = xchg(&ns->bacct, &acct->pin);
        mutex_unlock(&acct->lock);
        pin_kill(old);
        mnt_drop_write(mnt);
        mntput(mnt);
        return 0;
}

static DEFINE_MUTEX(acct_on_mutex);

/**
 * sys_acct - enable/disable process accounting
 * @name: file name for accounting records or NULL to shutdown accounting
 *
 * Returns 0 for success or negative errno values for failure.
 *
 * sys_acct() is the only system call needed to implement process
 * accounting. It takes the name of the file where accounting records
 * should be written. If the filename is NULL, accounting will be
 * shutdown.
 */
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);
                mutex_lock(&acct_on_mutex);
                error = acct_on(tmp);
                mutex_unlock(&acct_on_mutex);
                putname(tmp);
        } else {
                rcu_read_lock();
                pin_kill(task_active_pid_ns(current)->bacct);
        }

        return error;
}

void acct_exit_ns(struct pid_namespace *ns)
{
        rcu_read_lock();
        pin_kill(ns->bacct);
}

/*
 *  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.
 */

static void fill_ac(acct_t *ac)
{
        struct pacct_struct *pacct = &current->signal->pacct;
        u64 elapsed, run_time;
        struct tty_struct *tty;

        /*
         * 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*/
        run_time = ktime_get_ns();
        run_time -= current->group_leader->start_time;
        /* 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;
#if ACCT_VERSION==2
        ac->ac_ahz = AHZ;
#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(nsec_to_AHZ(pacct->ac_utime));
        ac->ac_stime = encode_comp_t(nsec_to_AHZ(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);
}
/*
 *  do_acct_process does all actual work. Caller holds the reference to file.
 */
static void do_acct_process(struct bsd_acct_struct *acct)
{
        acct_t ac;
        unsigned long flim;
        const struct cred *orig_cred;
        struct file *file = acct->file;

        /*
         * 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;
        /* 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))
                goto out;

        fill_ac(&ac);
        /* 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 == 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
        {
                struct pid_namespace *ns = acct->ns;

                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
        /*
         * Get freeze protection. If the fs is frozen, just skip the write
         * as we could deadlock the system otherwise.
         */
        if (file_start_write_trylock(file)) {
                /* it's been opened O_APPEND, so position is irrelevant */
                loff_t pos = 0;
                __kernel_write(file, (char *)&ac, sizeof(acct_t), &pos);
                file_end_write(file);
        }
out:
        current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
        revert_creds(orig_cred);
}

/**
 * acct_collect - collect accounting information into pacct_struct
 * @exitcode: task exit code
 * @group_dead: not 0, if this thread is the last one in the process.
 */
void acct_collect(long exitcode, int group_dead)
{
        struct pacct_struct *pacct = &current->signal->pacct;
        u64 utime, stime;
        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;

        task_cputime(current, &utime, &stime);
        pacct->ac_utime += utime;
        pacct->ac_stime += stime;
        pacct->ac_minflt += current->min_flt;
        pacct->ac_majflt += current->maj_flt;
        spin_unlock_irq(&current->sighand->siglock);
}

static void slow_acct_process(struct pid_namespace *ns)
{
        for ( ; ns; ns = ns->parent) {
                struct bsd_acct_struct *acct = acct_get(ns);
                if (acct) {
                        do_acct_process(acct);
                        mutex_unlock(&acct->lock);
                        acct_put(acct);
                }
        }
}

/**
 * acct_process
 *
 * handles process accounting for an exiting task
 */
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) {
                if (ns->bacct)
                        break;
        }
        if (unlikely(ns))
                slow_acct_process(ns);
}