Date: Mon, 5 Apr 1999 19:02:52 -0700 (PDT) From: Nick Sayer <nsayer@quack.kfu.com> To: hackers@freebsd.org Subject: Revised suggestion for securelevel negative time deltas Message-ID: <199904060202.TAA31558@medusa.kfu.com>
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Thanks to Garance A Droshihn for a better idea.
Attempts to negatively offset the clock are clamped to one second less
than the highest the clock has yet reached. This will allow xntpd
(or a miscreant, alas) to "freeze" the clock in place, but not
go backwards in time beyond a second.
Here is a proposed patch. Note the big blank spot where a proposal
for handling positive deltas should go. :-)
--- kern_time.c.orig Fri Apr 2 13:35:13 1999
+++ kern_time.c Fri Apr 2 13:34:11 1999
@@ -77,7 +77,8 @@
settime(tv)
struct timeval *tv;
{
- struct timeval delta, tv1;
+ struct timeval delta, tv1, tv2;
+ static struct timeval maxtime;
struct timespec ts;
int s;
@@ -88,13 +89,30 @@
/*
* If the system is secure, we do not allow the time to be
- * set to an earlier value (it may be slowed using adjtime,
- * but not set back). This feature prevent interlopers from
- * setting arbitrary time stamps on files.
+ * set to a value earlier than 1 second less than the highest
+ * time we have yet seen. The worst a miscreant can do in
+ * this circumstance is "freeze" time. He couldn't go
+ * back to the past.
*/
- if (delta.tv_sec < 0 && securelevel > 1) {
- splx(s);
- return (EPERM);
+ if (securelevel > 1) {
+ if (delta.tv_sec < 0 || delta.tv_usec < 0) {
+ if ( tv1.tv_sec > maxtime.tv_sec )
+ maxtime=tv1;
+ tv2=maxtime;
+ timevalsub( &tv2, &tv );
+ if ( tv2.tv_sec < -1 ) {
+ tv.tv_sec=maxtime.tv_sec-1;
+ }
+ }
+ else {
+ /* XXX
+ * We have to figure out how to be secure
+ * in this case. Allowing arbitrary
+ * positive increases allows a miscreant
+ * to simply wrap time around the end
+ * of time.
+ */
+ }
}
ts.tv_sec = tv->tv_sec;
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