linux-kernel - [PATCH] ktime_t overflow from sys

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Message-ID: <20060827083438.GA6931@var.cx>
Date:	Sun, 27 Aug 2006 10:34:38 +0200
From:	Frank v Waveren <fvw@....cx>
To:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] ktime_t overflow from sys_nanosleep

On systems where longs are 64 bits, nanosleep can pass a timespec with
tv_sec larger than 18446744073 (approx 2^34), which is then multiplied 
by NSEC_PER_SEC and stuffed into a single s64 by ktime_set in
hrtimer_nanosleep. This overflows of course, and causes the sleep to
return early (instantly if you set the timespec to its maximum).

(this gets triggered by doing a "sleep inf" with the sleep from the
gnu coreutils).

I can think of two solutions, either increase the size of ktime_t to
something larger than 64 bits, which would probably bring along a host
of issues and and lose the entire point of having a single scalar, or
we can limit the range of sys_nanosleep, which is simple, but will have
to be documented and sleep(1) will still need fixing.

I've put the check in timespec_valid in the attached patch. This will
limit the range of timespecs in general, but since most of them seem
to end up as ktime_t's anyway, it seems like a reasonable precaution.

Signed-off-by: Frank v Waveren <fvw@....cx>

diff -urpN linux-2.6.17.11/include/linux/time.h linux-2.6.17.11-fvw/include/linux/time.h
--- linux-2.6.17.11/include/linux/time.h	2006-08-23 23:16:33.000000000 +0200
+++ linux-2.6.17.11-fvw/include/linux/time.h	2006-08-27 10:21:07.000000000 +0200
@@ -68,11 +68,13 @@ extern unsigned long mktime(const unsign
 extern void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec);

 /*
- * Returns true if the timespec is norm, false if denorm:
+ * Returns true iff the timespec nanoseconds is less than one second 
+ * ("normalised") and the seconds is in the range 0..2**31:
  */
 #define timespec_valid(ts) \
-	(((ts)->tv_sec >= 0) && (((unsigned long) (ts)->tv_nsec) < NSEC_PER_SEC))
-
+        (((ts)->tv_sec >= 0) && (((ts)->tv_sec) <= (~(1<<31))) && \
+        (((unsigned long) (ts)->tv_nsec) < NSEC_PER_SEC))
+          
 extern struct timespec xtime;
 extern struct timespec wall_to_monotonic;
 extern seqlock_t xtime_lock;

-- 
Frank v Waveren                                  Key fingerprint: BDD7 D61E
fvw@....cx                                              5D39 CF05 4BFC F57A
Public key: hkp://wwwkeys.pgp.net/468D62C8              FA00 7D51 468D 62C8

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