ntpd doesn't like ASLR on stable/12 post-r350672

[Konstantin Belousov]

On Sun, Aug 25, 2019 at 12:40:22AM +0200, Trond Endrestøl wrote:
> On Sun, 25 Aug 2019 01:28+0300, Konstantin Belousov wrote:
> 
> > On Sun, Aug 25, 2019 at 12:19:43AM +0200, Trond Endrestøl wrote:
> > > On Sat, 24 Aug 2019 23:41+0300, Konstantin Belousov wrote:
> > > > > I tried changing command="/usr/sbin/${name}" to 
> > > > > command="/usr/bin/proccontrol -m aslr -s disable /usr/sbin/${name}" in 
> > > > > /etc/rc.d/ntpd, but that didn't go well.
> > > > 
> > > > If you set kern.elf64.aslr.stack_gap to zero, does it help ?
> > > 
> > > That helped. Thank you again.
> > 
> > Can you verify is ntpd sets new rlimit(RLIMIT_STACK) for the main thread,
> > and if yes, what this new limit is ?
> 
> (gdb)
> 5265                            if (-1 == setrlimit(RLIMIT_STACK, &rl)) {
> (gdb) print rl
> $1 = {rlim_cur = 204800, rlim_max = 536870912}
So they set the stack limit to 200K, am I right ?  I suspect they do
that because ntpd wires entire process address space, so 512M blows off
all limits on wiring.

I do not have a good idea how to make this behaviour compatible with
the gap.  Might be we can change the gap sizing parameter to KBs instead
of percentage, and set the defaults in 64KB range.

> 
> > aslr.stack_gap is the percentage for the gap on that stack, and since
> > default size of the main stack limit is quite large 512M, even 3%
> > (default gap upper limit) are whole 15M. If the new limit is less than
> > 15M, there is a likely probability that only the gap is left after the
> > rlimit(2) call, leaving no space for the program frames.
> > 
> > At least this looks like a nice theory.
> 
> -- 
> Trond.