https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199673
Bug ID: 199673
Summary: sysctl(8) suffers a multiplication overflow when
formatting vm.vmtotal
Product: Base System
Version: 10.0-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: bin
Assignee: freebsd-bugs@FreeBSD.org
Reporter: vmage...@gmail.com
Created attachment 155955
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=155955&action=edit
sysctl-overflow.diff
Here's a part of 'sysctl vm.mvtotal' output on my 10.0/amd64
machine:
% sysctl vm.vmtotal
[...]
Virtual Memory: (Total: 1654588K Active: 1536668K)
[...]
If on the other hand, when I try to retrieve the same data via
sysctl(3), I get different total virtual memory:
% cat >test.c <<'EOF'
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>
int main() {
struct vmtotal vt = {0};
size_t vtlen = sizeof(vt);
if (sysctlbyname("vm.vmtotal", &vt, &vtlen, NULL, 0) != 0)
return -1;
ssize_t pagesize = getpagesize()/1024;
printf("vm.vmtotal.t_vm = %zd pages (%zd kB)\n",
(ssize_t)vt.t_vm,
pagesize*vt.t_vm);
return 0;
}
'EOF'
% c99 test.c && ./a.out
vm.vmtotal.t_vm = 1074154446 pages (4296617784 kB)
As you can see, the actual data coming out of sysctl(3) is
4296617784K, not 1654588K as sysctl(8) says. This is because
sysctl(8) has a multiplication overflow in the 'S_vmtotal'
function [1] when the number of pages ('t_vm') is multiplied by
the page size ('pageKilo').
I'm attaching a (completely untested) patch to fix this problem;
apply this patch to 'sbin/sysctl/sysctl.c'.
[1]
http://svnweb.freebsd.org/base/head/sbin/sysctl/sysctl.c?revision=278654&view=markup#l530
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