Re: [stable 2.6.24] WARNING: at kernel/time/clockevents.c

Thomas Gleixner
2008-02-13T09:38:34Z

On Wed, 13 Feb 2008, Frans Pop wrote:
> On Wednesday 13 February 2008, Thomas Gleixner wrote:
> > On Tue, 12 Feb 2008, Andrew Morton wrote:
> > > On Sun, 10 Feb 2008 14:40:21 +0100 Frans Pop <elendil@planet.nl> wrote:
> > > the hrtimer code is preparing an invalid ktime_t. Note that
> > > clockevents_program_event() actually fails when this happens - I am
> > > surprised that this is not causing observeable userspace problems.
> > >
> > > The WARN_ON_ONCE() means that you'll only see this warning once per
> > > boot. But the actually error could be happening any number of times
> > > without being reported.
> > >
> > > Looks pretty serious?
> >
> > Yes. It's the same problem, which got fixed with:
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit
> >;h=62f0f61e6673e67151a7c8c0f9a09c7ea43fe2b5
>
> OK, so probably glibc performs a unit test during build that asks for a long
> sleep. I guess that makes sense.

Frans,

can you please apply the following patch ? I really should have
thought about that, when I fixed the above one.

Thanks,
tglx

------------>

Subject: hrtimer: check relative timeouts for overflow
From: Thomas Gleixner <tglx@linutronix.de>

Various user space callers ask for relative timeouts. While we fixed
that overflow issue in hrtimer_start(), the sites which convert
relative user space values to absolute timeouts themself were uncovered.

Instead of putting overflow checks into each place add a function
which does the sanity checking and convert all affected callers to use
it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/ktime.h | 2 ++
kernel/futex.c | 2 +-
kernel/futex_compat.c | 2 +-
kernel/hrtimer.c | 33 ++++++++++++++++-----------------
kernel/posix-timers.c | 8 +++++---
5 files changed, 25 insertions(+), 22 deletions(-)

Index: linux-2.6-hrt/include/linux/ktime.h
===================================================================
--- linux-2.6-hrt.orig/include/linux/ktime.h
+++ linux-2.6-hrt/include/linux/ktime.h
@@ -310,6 +310,8 @@ static inline ktime_t ktime_sub_us(const
return ktime_sub_ns(kt, usec * 1000);
}

+extern ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs);
+
/*
* The resolution of the clocks. The resolution value is returned in
* the clock_getres() system call to give application programmers an
Index: linux-2.6-hrt/kernel/futex.c
===================================================================
--- linux-2.6-hrt.orig/kernel/futex.c
+++ linux-2.6-hrt/kernel/futex.c
@@ -2116,7 +2116,7 @@ asmlinkage long sys_futex(u32 __user *ua

t = timespec_to_ktime(ts);
if (cmd == FUTEX_WAIT)
- t = ktime_add(ktime_get(), t);
+ t = ktime_add_safe(ktime_get(), t);
tp = &t;
}
/*
Index: linux-2.6-hrt/kernel/futex_compat.c
===================================================================
--- linux-2.6-hrt.orig/kernel/futex_compat.c
+++ linux-2.6-hrt/kernel/futex_compat.c
@@ -176,7 +176,7 @@ asmlinkage long compat_sys_futex(u32 __u

t = timespec_to_ktime(ts);
if (cmd == FUTEX_WAIT)
- t = ktime_add(ktime_get(), t);
+ t = ktime_add_safe(ktime_get(), t);
tp = &t;
}
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE)
Index: linux-2.6-hrt/kernel/hrtimer.c
===================================================================
--- linux-2.6-hrt.orig/kernel/hrtimer.c
+++ linux-2.6-hrt/kernel/hrtimer.c
@@ -326,6 +326,19 @@ u64 ktime_divns(const ktime_t kt, s64 di
#endif /* BITS_PER_LONG >= 64 */

/*
+ * Add two ktime values and do a safety check for overflow:
+ */
+ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs)
+{
+ ktime_t res = ktime_add(lhs, rhs);
+
+ if (res.tv64 < 0 || res.tv64 < lhs.tv64 || res.tv64 < rhs.tv64)
+ res.tv64 = KTIME_MAX;
+
+ return res;
+}
+
+/*
* Check, whether the timer is on the callback pending list
*/
static inline int hrtimer_cb_pending(const struct hrtimer *timer)
@@ -682,13 +695,7 @@ u64 hrtimer_forward(struct hrtimer *time
*/
orun++;
}
- timer->expires = ktime_add(timer->expires, interval);
- /*
- * Make sure, that the result did not wrap with a very large
- * interval.
- */
- if (timer->expires.tv64 < 0)
- timer->expires = ktime_set(KTIME_SEC_MAX, 0);
+ timer->expires = ktime_add_safe(timer->expires, interval);

return orun;
}
@@ -839,7 +846,7 @@ hrtimer_start(struct hrtimer *timer, kti
new_base = switch_hrtimer_base(timer, base);

if (mode == HRTIMER_MODE_REL) {
- tim = ktime_add(tim, new_base->get_time());
+ tim = ktime_add_safe(tim, new_base->get_time());
/*
* CONFIG_TIME_LOW_RES is a temporary way for architectures
* to signal that they simply return xtime in
@@ -848,16 +855,8 @@ hrtimer_start(struct hrtimer *timer, kti
* timeouts. This will go away with the GTOD framework.
*/
#ifdef CONFIG_TIME_LOW_RES
- tim = ktime_add(tim, base->resolution);
+ tim = ktime_add_safe(tim, base->resolution);
#endif
- /*
- * Careful here: User space might have asked for a
- * very long sleep, so the add above might result in a
- * negative number, which enqueues the timer in front
- * of the queue.
- */
- if (tim.tv64 < 0)
- tim.tv64 = KTIME_MAX;
}
timer->expires = tim;

Index: linux-2.6-hrt/kernel/posix-timers.c
===================================================================
--- linux-2.6-hrt.orig/kernel/posix-timers.c
+++ linux-2.6-hrt/kernel/posix-timers.c
@@ -767,9 +767,11 @@ common_timer_set(struct k_itimer *timr,
/* SIGEV_NONE timers are not queued ! See common_timer_get */
if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) {
/* Setup correct expiry time for relative timers */
- if (mode == HRTIMER_MODE_REL)
- timer->expires = ktime_add(timer->expires,
- timer->base->get_time());
+ if (mode == HRTIMER_MODE_REL) {
+ timer->expires =
+ ktime_add_safe(timer->expires,
+ timer->base->get_time());
+ }
return 0;
}