Author: cem
Date: Sun Feb 10 23:07:46 2019
New Revision: 343985
URL: https://svnweb.freebsd.org/changeset/base/343985
Log:
Prevent overflow for usertime/systime in caclru1
PR: 76972 and duplicates
Reported by: Dr. Christopher Landauer <cal AT aero.org>,
Steinar Haug <sthaug AT nethelp.no>
Submitted by: Andrey Zonov <andrey AT zonov.org> (earlier version)
MFC after: 2 weeks
Modified:
head/sys/kern/kern_resource.c
Modified: head/sys/kern/kern_resource.c
==============================================================================
--- head/sys/kern/kern_resource.c Sun Feb 10 22:33:41 2019
(r343984)
+++ head/sys/kern/kern_resource.c Sun Feb 10 23:07:46 2019
(r343985)
@@ -863,6 +863,15 @@ rufetchtd(struct thread *td, struct rusage *ru)
calcru1(p, &td->td_rux, &ru->ru_utime, &ru->ru_stime);
}
+static uint64_t
+mul64_by_fraction(uint64_t a, uint64_t b, uint64_t c)
+{
+ /*
+ * Compute floor(a * (b / c)) without overflowing, (b / c) <= 1.0.
+ */
+ return ((a / c) * b + (a % c) * (b / c) + (a % c) * (b % c) / c);
+}
+
static void
calcru1(struct proc *p, struct rusage_ext *ruxp, struct timeval *up,
struct timeval *sp)
@@ -892,10 +901,10 @@ calcru1(struct proc *p, struct rusage_ext *ruxp, struc
* The normal case, time increased.
* Enforce monotonicity of bucketed numbers.
*/
- uu = (tu * ut) / tt;
+ uu = mul64_by_fraction(tu, ut, tt);
if (uu < ruxp->rux_uu)
uu = ruxp->rux_uu;
- su = (tu * st) / tt;
+ su = mul64_by_fraction(tu, st, tt);
if (su < ruxp->rux_su)
su = ruxp->rux_su;
} else if (tu + 3 > ruxp->rux_tu || 101 * tu > 100 * ruxp->rux_tu) {
@@ -924,8 +933,8 @@ calcru1(struct proc *p, struct rusage_ext *ruxp, struc
"to %ju usec for pid %d (%s)\n",
(uintmax_t)ruxp->rux_tu, (uintmax_t)tu,
p->p_pid, p->p_comm);
- uu = (tu * ut) / tt;
- su = (tu * st) / tt;
+ uu = mul64_by_fraction(tu, ut, tt);
+ su = mul64_by_fraction(tu, st, tt);
}
ruxp->rux_uu = uu;
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