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More secure clock management. Allow positive steps only once per second

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for as much as one second, but no more. Allows a miscreant to
double-time march the clock, but no worse.

XXX Unlike putting negative deltas in a while(1), performing small
positive steps inside of a while(1) will return EPERM for the
unpermitted ones. Repeated negative deltas are clamped without
error (but the kernel does log a notice).
This commit is contained in:
Nick Sayer 1999-04-07 19:48:09 +00:00
parent 3f92429a24
commit c0bd94a75d
1 changed files with 16 additions and 11 deletions
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27
sys/kern/kern_time.c
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@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)kern_time.c 8.1 (Berkeley) 6/10/93
* $Id: kern_time.c,v 1.62 1999/04/07 16:36:56 nsayer Exp $
* $Id: kern_time.c,v 1.63 1999/04/07 17:32:21 mjacob Exp $
*/
#include <sys/param.h>
@ -79,7 +79,7 @@ settime(tv)
struct timeval *tv;
{
struct timeval delta, tv1, tv2;
static struct timeval maxtime;
static struct timeval maxtime, laststep;
struct timespec ts;
int s;
@ -94,11 +94,15 @@ settime(tv)
* 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.
*
* We similarly do not allow the clock to be stepped more
* than one second, nor more than once per second. This allows
* a miscreant to make the clock march double-time, but no worse.
*/
if (securelevel > 1) {
if (delta.tv_sec < 0 || delta.tv_usec < 0) {
/*
* Initialize maxtime if we've not seen it before.
* Update maxtime to latest time we've seen.
*/
if (tv1.tv_sec > maxtime.tv_sec)
maxtime = tv1;
@ -109,14 +113,15 @@ settime(tv)
printf("Time adjustment clamped to -1 second\n");
}
} 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.
*/
if (tv1.tv_sec == laststep.tv_sec) {
splx(s);
return (EPERM);
}
if (delta.tv_sec > 1) {
tv->tv_sec = tv1.tv_sec + 1;
printf("Time adjustment clamped to +1 second\n");
}
laststep = *tv;
}
}