linux/fs/timerfd.c
Thomas Gleixner 1e38da300e timerfd: Protect the might cancel mechanism proper
The handling of the might_cancel queueing is not properly protected, so
parallel operations on the file descriptor can race with each other and
lead to list corruptions or use after free.

Protect the context for these operations with a seperate lock.

The wait queue lock cannot be reused for this because that would create a
lock inversion scenario vs. the cancel lock. Replacing might_cancel with an
atomic (atomic_t or atomic bit) does not help either because it still can
race vs. the actual list operation.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "linux-fsdevel@vger.kernel.org"
Cc: syzkaller <syzkaller@googlegroups.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1701311521430.3457@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2017-02-10 11:15:09 +01:00

590 lines
13 KiB
C

/*
* fs/timerfd.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
*
*
* Thanks to Thomas Gleixner for code reviews and useful comments.
*
*/
#include <linux/alarmtimer.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
#include <linux/anon_inodes.h>
#include <linux/timerfd.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <linux/rcupdate.h>
struct timerfd_ctx {
union {
struct hrtimer tmr;
struct alarm alarm;
} t;
ktime_t tintv;
ktime_t moffs;
wait_queue_head_t wqh;
u64 ticks;
int clockid;
short unsigned expired;
short unsigned settime_flags; /* to show in fdinfo */
struct rcu_head rcu;
struct list_head clist;
spinlock_t cancel_lock;
bool might_cancel;
};
static LIST_HEAD(cancel_list);
static DEFINE_SPINLOCK(cancel_lock);
static inline bool isalarm(struct timerfd_ctx *ctx)
{
return ctx->clockid == CLOCK_REALTIME_ALARM ||
ctx->clockid == CLOCK_BOOTTIME_ALARM;
}
/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
* tintv != 0) until the timer is accessed.
*/
static void timerfd_triggered(struct timerfd_ctx *ctx)
{
unsigned long flags;
spin_lock_irqsave(&ctx->wqh.lock, flags);
ctx->expired = 1;
ctx->ticks++;
wake_up_locked(&ctx->wqh);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}
static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
{
struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
t.tmr);
timerfd_triggered(ctx);
return HRTIMER_NORESTART;
}
static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
ktime_t now)
{
struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
t.alarm);
timerfd_triggered(ctx);
return ALARMTIMER_NORESTART;
}
/*
* Called when the clock was set to cancel the timers in the cancel
* list. This will wake up processes waiting on these timers. The
* wake-up requires ctx->ticks to be non zero, therefore we increment
* it before calling wake_up_locked().
*/
void timerfd_clock_was_set(void)
{
ktime_t moffs = ktime_mono_to_real(0);
struct timerfd_ctx *ctx;
unsigned long flags;
rcu_read_lock();
list_for_each_entry_rcu(ctx, &cancel_list, clist) {
if (!ctx->might_cancel)
continue;
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->moffs != moffs) {
ctx->moffs = KTIME_MAX;
ctx->ticks++;
wake_up_locked(&ctx->wqh);
}
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}
rcu_read_unlock();
}
static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
if (ctx->might_cancel) {
ctx->might_cancel = false;
spin_lock(&cancel_lock);
list_del_rcu(&ctx->clist);
spin_unlock(&cancel_lock);
}
}
static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
spin_lock(&ctx->cancel_lock);
__timerfd_remove_cancel(ctx);
spin_unlock(&ctx->cancel_lock);
}
static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
return false;
ctx->moffs = ktime_mono_to_real(0);
return true;
}
static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
spin_lock(&ctx->cancel_lock);
if ((ctx->clockid == CLOCK_REALTIME ||
ctx->clockid == CLOCK_REALTIME_ALARM) &&
(flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
if (!ctx->might_cancel) {
ctx->might_cancel = true;
spin_lock(&cancel_lock);
list_add_rcu(&ctx->clist, &cancel_list);
spin_unlock(&cancel_lock);
}
} else {
__timerfd_remove_cancel(ctx);
}
spin_unlock(&ctx->cancel_lock);
}
static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
ktime_t remaining;
if (isalarm(ctx))
remaining = alarm_expires_remaining(&ctx->t.alarm);
else
remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
return remaining < 0 ? 0: remaining;
}
static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
const struct itimerspec *ktmr)
{
enum hrtimer_mode htmode;
ktime_t texp;
int clockid = ctx->clockid;
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
texp = timespec_to_ktime(ktmr->it_value);
ctx->expired = 0;
ctx->ticks = 0;
ctx->tintv = timespec_to_ktime(ktmr->it_interval);
if (isalarm(ctx)) {
alarm_init(&ctx->t.alarm,
ctx->clockid == CLOCK_REALTIME_ALARM ?
ALARM_REALTIME : ALARM_BOOTTIME,
timerfd_alarmproc);
} else {
hrtimer_init(&ctx->t.tmr, clockid, htmode);
hrtimer_set_expires(&ctx->t.tmr, texp);
ctx->t.tmr.function = timerfd_tmrproc;
}
if (texp != 0) {
if (isalarm(ctx)) {
if (flags & TFD_TIMER_ABSTIME)
alarm_start(&ctx->t.alarm, texp);
else
alarm_start_relative(&ctx->t.alarm, texp);
} else {
hrtimer_start(&ctx->t.tmr, texp, htmode);
}
if (timerfd_canceled(ctx))
return -ECANCELED;
}
ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
return 0;
}
static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;
timerfd_remove_cancel(ctx);
if (isalarm(ctx))
alarm_cancel(&ctx->t.alarm);
else
hrtimer_cancel(&ctx->t.tmr);
kfree_rcu(ctx, rcu);
return 0;
}
static unsigned int timerfd_poll(struct file *file, poll_table *wait)
{
struct timerfd_ctx *ctx = file->private_data;
unsigned int events = 0;
unsigned long flags;
poll_wait(file, &ctx->wqh, wait);
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->ticks)
events |= POLLIN;
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return events;
}
static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct timerfd_ctx *ctx = file->private_data;
ssize_t res;
u64 ticks = 0;
if (count < sizeof(ticks))
return -EINVAL;
spin_lock_irq(&ctx->wqh.lock);
if (file->f_flags & O_NONBLOCK)
res = -EAGAIN;
else
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
/*
* If clock has changed, we do not care about the
* ticks and we do not rearm the timer. Userspace must
* reevaluate anyway.
*/
if (timerfd_canceled(ctx)) {
ctx->ticks = 0;
ctx->expired = 0;
res = -ECANCELED;
}
if (ctx->ticks) {
ticks = ctx->ticks;
if (ctx->expired && ctx->tintv) {
/*
* If tintv != 0, this is a periodic timer that
* needs to be re-armed. We avoid doing it in the timer
* callback to avoid DoS attacks specifying a very
* short timer period.
*/
if (isalarm(ctx)) {
ticks += alarm_forward_now(
&ctx->t.alarm, ctx->tintv) - 1;
alarm_restart(&ctx->t.alarm);
} else {
ticks += hrtimer_forward_now(&ctx->t.tmr,
ctx->tintv) - 1;
hrtimer_restart(&ctx->t.tmr);
}
}
ctx->expired = 0;
ctx->ticks = 0;
}
spin_unlock_irq(&ctx->wqh.lock);
if (ticks)
res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
return res;
}
#ifdef CONFIG_PROC_FS
static void timerfd_show(struct seq_file *m, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;
struct itimerspec t;
spin_lock_irq(&ctx->wqh.lock);
t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
t.it_interval = ktime_to_timespec(ctx->tintv);
spin_unlock_irq(&ctx->wqh.lock);
seq_printf(m,
"clockid: %d\n"
"ticks: %llu\n"
"settime flags: 0%o\n"
"it_value: (%llu, %llu)\n"
"it_interval: (%llu, %llu)\n",
ctx->clockid,
(unsigned long long)ctx->ticks,
ctx->settime_flags,
(unsigned long long)t.it_value.tv_sec,
(unsigned long long)t.it_value.tv_nsec,
(unsigned long long)t.it_interval.tv_sec,
(unsigned long long)t.it_interval.tv_nsec);
}
#else
#define timerfd_show NULL
#endif
#ifdef CONFIG_CHECKPOINT_RESTORE
static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct timerfd_ctx *ctx = file->private_data;
int ret = 0;
switch (cmd) {
case TFD_IOC_SET_TICKS: {
u64 ticks;
if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
return -EFAULT;
if (!ticks)
return -EINVAL;
spin_lock_irq(&ctx->wqh.lock);
if (!timerfd_canceled(ctx)) {
ctx->ticks = ticks;
wake_up_locked(&ctx->wqh);
} else
ret = -ECANCELED;
spin_unlock_irq(&ctx->wqh.lock);
break;
}
default:
ret = -ENOTTY;
break;
}
return ret;
}
#else
#define timerfd_ioctl NULL
#endif
static const struct file_operations timerfd_fops = {
.release = timerfd_release,
.poll = timerfd_poll,
.read = timerfd_read,
.llseek = noop_llseek,
.show_fdinfo = timerfd_show,
.unlocked_ioctl = timerfd_ioctl,
};
static int timerfd_fget(int fd, struct fd *p)
{
struct fd f = fdget(fd);
if (!f.file)
return -EBADF;
if (f.file->f_op != &timerfd_fops) {
fdput(f);
return -EINVAL;
}
*p = f;
return 0;
}
SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
{
int ufd;
struct timerfd_ctx *ctx;
/* Check the TFD_* constants for consistency. */
BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
if ((flags & ~TFD_CREATE_FLAGS) ||
(clockid != CLOCK_MONOTONIC &&
clockid != CLOCK_REALTIME &&
clockid != CLOCK_REALTIME_ALARM &&
clockid != CLOCK_BOOTTIME &&
clockid != CLOCK_BOOTTIME_ALARM))
return -EINVAL;
if (!capable(CAP_WAKE_ALARM) &&
(clockid == CLOCK_REALTIME_ALARM ||
clockid == CLOCK_BOOTTIME_ALARM))
return -EPERM;
ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
init_waitqueue_head(&ctx->wqh);
spin_lock_init(&ctx->cancel_lock);
ctx->clockid = clockid;
if (isalarm(ctx))
alarm_init(&ctx->t.alarm,
ctx->clockid == CLOCK_REALTIME_ALARM ?
ALARM_REALTIME : ALARM_BOOTTIME,
timerfd_alarmproc);
else
hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
ctx->moffs = ktime_mono_to_real(0);
ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
if (ufd < 0)
kfree(ctx);
return ufd;
}
static int do_timerfd_settime(int ufd, int flags,
const struct itimerspec *new,
struct itimerspec *old)
{
struct fd f;
struct timerfd_ctx *ctx;
int ret;
if ((flags & ~TFD_SETTIME_FLAGS) ||
!timespec_valid(&new->it_value) ||
!timespec_valid(&new->it_interval))
return -EINVAL;
ret = timerfd_fget(ufd, &f);
if (ret)
return ret;
ctx = f.file->private_data;
if (!capable(CAP_WAKE_ALARM) && isalarm(ctx)) {
fdput(f);
return -EPERM;
}
timerfd_setup_cancel(ctx, flags);
/*
* We need to stop the existing timer before reprogramming
* it to the new values.
*/
for (;;) {
spin_lock_irq(&ctx->wqh.lock);
if (isalarm(ctx)) {
if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
break;
} else {
if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
break;
}
spin_unlock_irq(&ctx->wqh.lock);
cpu_relax();
}
/*
* If the timer is expired and it's periodic, we need to advance it
* because the caller may want to know the previous expiration time.
* We do not update "ticks" and "expired" since the timer will be
* re-programmed again in the following timerfd_setup() call.
*/
if (ctx->expired && ctx->tintv) {
if (isalarm(ctx))
alarm_forward_now(&ctx->t.alarm, ctx->tintv);
else
hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
}
old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
old->it_interval = ktime_to_timespec(ctx->tintv);
/*
* Re-program the timer to the new value ...
*/
ret = timerfd_setup(ctx, flags, new);
spin_unlock_irq(&ctx->wqh.lock);
fdput(f);
return ret;
}
static int do_timerfd_gettime(int ufd, struct itimerspec *t)
{
struct fd f;
struct timerfd_ctx *ctx;
int ret = timerfd_fget(ufd, &f);
if (ret)
return ret;
ctx = f.file->private_data;
spin_lock_irq(&ctx->wqh.lock);
if (ctx->expired && ctx->tintv) {
ctx->expired = 0;
if (isalarm(ctx)) {
ctx->ticks +=
alarm_forward_now(
&ctx->t.alarm, ctx->tintv) - 1;
alarm_restart(&ctx->t.alarm);
} else {
ctx->ticks +=
hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
- 1;
hrtimer_restart(&ctx->t.tmr);
}
}
t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
t->it_interval = ktime_to_timespec(ctx->tintv);
spin_unlock_irq(&ctx->wqh.lock);
fdput(f);
return 0;
}
SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
const struct itimerspec __user *, utmr,
struct itimerspec __user *, otmr)
{
struct itimerspec new, old;
int ret;
if (copy_from_user(&new, utmr, sizeof(new)))
return -EFAULT;
ret = do_timerfd_settime(ufd, flags, &new, &old);
if (ret)
return ret;
if (otmr && copy_to_user(otmr, &old, sizeof(old)))
return -EFAULT;
return ret;
}
SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
{
struct itimerspec kotmr;
int ret = do_timerfd_gettime(ufd, &kotmr);
if (ret)
return ret;
return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
const struct compat_itimerspec __user *, utmr,
struct compat_itimerspec __user *, otmr)
{
struct itimerspec new, old;
int ret;
if (get_compat_itimerspec(&new, utmr))
return -EFAULT;
ret = do_timerfd_settime(ufd, flags, &new, &old);
if (ret)
return ret;
if (otmr && put_compat_itimerspec(otmr, &old))
return -EFAULT;
return ret;
}
COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
struct compat_itimerspec __user *, otmr)
{
struct itimerspec kotmr;
int ret = do_timerfd_gettime(ufd, &kotmr);
if (ret)
return ret;
return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
}
#endif