svn commit: r359053 - head/sys/kern

[Ian Lepore]

On Tue, 2020-03-17 at 17:05 -0700, John Baldwin wrote:
> On 3/17/20 3:36 PM, Ian Lepore wrote:
> > On Tue, 2020-03-17 at 22:27 +0000, Conrad Meyer wrote:
> > > Author: cem
> > > Date: Tue Mar 17 22:27:16 2020
> > > New Revision: 359053
> > > URL: https://svnweb.freebsd.org/changeset/base/359053
> > > 
> > > Log:
> > >   Implement sysctl kern.boot_id
> > >   
> > >   Boot IDs are random, opaque 128-bit identifiers that
> > > distinguish distinct
> > >   system boots.  A new ID is generated each time the system
> > > boots.  Unlike
> > >   kern.boottime, the value is not modified by NTP
> > > adjustments.  It remains fixed
> > >   until the machine is restarted.
> > >   
> > >   PR:		244867
> > >   Reported by:	Ricardo Fraile <rfraile AT rfraile.eu>
> > >   MFC after:	I do not intend to, but feel free
> > > 
> > > Modified:
> > >   head/sys/kern/kern_mib.c
> > > 
> > > Modified: head/sys/kern/kern_mib.c
> > > =================================================================
> > > =============
> > > --- head/sys/kern/kern_mib.c	Tue Mar 17 21:29:03 2020	(
> > > r359052)
> > > +++ head/sys/kern/kern_mib.c	Tue Mar 17 22:27:16 2020	(
> > > r359053)
> > > @@ -448,6 +448,32 @@ SYSCTL_PROC(_kern, KERN_HOSTID, hostid,
> > >      CTLTYPE_ULONG | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_MPSAFE
> > > | CTLFLAG_CAPRD,
> > >      NULL, 0, sysctl_hostid, "LU", "Host ID");
> > >  
> > > +static struct mtx bootid_lk;
> > > +MTX_SYSINIT(bootid_lock, &bootid_lk, "bootid generator lock",
> > > MTX_DEF);
> > > +
> > > +static int
> > > +sysctl_bootid(SYSCTL_HANDLER_ARGS)
> > > +{
> > > +	static uint8_t boot_id[16];
> > > +	static bool initialized = false;
> > > +
> > > +	mtx_lock(&bootid_lk);
> > > +	if (!initialized) {
> > > +		if (!is_random_seeded()) {
> > > +			mtx_unlock(&bootid_lk);
> > > +			return (ENXIO);
> > > +		}
> > > +		arc4random_buf(boot_id, sizeof(boot_id));
> > > +		initialized = true;
> > > +	}
> > > +	mtx_unlock(&bootid_lk);
> > > +
> > > +	return (SYSCTL_OUT(req, boot_id, sizeof(boot_id)));
> > > +}
> > > +SYSCTL_PROC(_kern, OID_AUTO, boot_id,
> > > +    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_MPSAFE |
> > > CTLFLAG_CAPRD,
> > > +    NULL, 0, sysctl_bootid, "", "Random boot ID");
> > > +
> > >  /*
> > >   * The osrelease string is copied from the global (osrelease in
> > > vers.c) into
> > >   * prison0 by a sysinit and is inherited by child jails if not
> > > changed at jail
> > 
> > This seems a bit complex.  Why run a sysinit to init a mutex so
> > that
> > you can safely do a lazy init of boot_id?  Seems like it would be
> > much
> > easier to just use a sysinit at SI_SUB_LAST to init boot_id before
> > sysctl can reference it.
> 
> Presumably you may not have enough entropy by SI_SUB_LAST to generate
> it?
> 

I thought arc4random in the kernel could provide random numbers
immediately (and definitely after jitter in device attachment times at
the end of kernel init)?  This doesn't seem like the kind of thing that
needs crypto-strength randomness.

-- Ian