FreeBSD Patch question

Robert Watson rwatson at
Thu Sep 25 13:13:56 PDT 2003

On Thu, 25 Sep 2003, V. Jones wrote:

> I administer a remote server and want to apply some of the security
> patches.  (I assume this is the best way to go since I can't go into
> single-user mode to use CVsup). 

I generally follow the following practice:

  cvsup in multiuser
  buildworld in multiuser
  buildkernel in multiuser

These stages, other than impact on cpu, memory, disk i/o speed, and
storage space, shouldn't interact with the running environment and so
shouldn't be a problem.  Then comes the slightly more tricky bit: I decide
whether I'm willing to update while running multiuser.  If I am:


If I'm not, the procedure is much the same except that I boot only to
single-user after the first reboot, mount -a, swapon, and proceed. 

Note that there are a number of risks and complications associated with
the installworld and mergemaster steps, both in multiuser and singleuser
mode.  multiuser is typically more risky: for example, if mergemaster
notices a change to MAKEDEV, it will prompt to recreate devices.  DO NOT
DO THIS ON A LIVE MULTIUSER SYSTEM. :-)  If you do run it, it will reset
all the permissions in /dev, leaving in-use ttys world readable and
writable.  This will permit unprivileged users to potentially sniff the
I/O for more privileged users, send output to their display, etc. So it's
fine in single-user, but not multi-user.  Typically, that sort of change
doesn't occur on the security/release branches, but will happen with
moderate frequency as you track -STABLE.

> I have a couple of questions.  First, I have installed one of the pgp
> ports to verify the patches.  When I run it, I get this message: 
> > File 'buffer46.patch.asc' has signature, but with no text.
> > Text is assumed to be in file 'buffer46.patch'.
> > signature not checked.
> >  Signature made 2003/09/17 18:02 GMT
> >  key does not meet validity threshold.
> > WARNING:  Because this public key is not certified with a trusted
> > signature, it is not known with high confidence that this public key
> > actually belongs to: "(KeyID: 0xCA6CDFB2)".
> I guess that I need to do some additional set up to get pgp to validate
> this file.  Can anyone tell me where to find a howto on this subject or
> tell me what to do?

PGP relies on a "web of trust".  Users sign each others identities to bind
them to keys.  Your local PGP keyring will hold any keys and signatures
you've stuffed in there.  PGP determines "trust" by building a path of
signatures and validations between you and the target key.  There are
various parameters to determine the degree of transitivity to trust, etc.
There's fairly extensive documentation of the PGP trust model on various
web pages, but you can read the above warning as simply "There is no path
of signatures between your trusted keys and the key used to sign this
message/file".  For the highest level of confidence, attend a USENIX or
BSDCon key signing, and sign the security-officer key yourself once you've
seen the fingerprint, etc.  For lower levels of confidence, go to a
key-signing event with someone who has signed the security-officer key,
etc, etc.

> Second, Do I have apply each patch, then run make after each patch, or
> can I apply all the patches and just run make once?

It depends a bit on the patches and the branch.  If you're tracking a
release/patch branch, you can cvsup forward to the head of the branch,
then rebuild the identified components.  Sometimes, patches and update
activities coallesce well (unrelated change to unrelated binaries).
Sometimes, less well -- you might have to make sure to build libraries
before binaries, for example, or apply a series of sendmail or ssh patches
in order.  Cvsuping forward and rebuilding world and kernel is a
reasonable answer for most people, and means you don't have to worry about
the ordering.

FYI, regarding your general interest in advice: the single best piece of
advice for remotely administered systems is to get a serial console.  That
way if something gets messed up, you have a decent chance of being able to
fix it.  It means you have full access to single-user mode, you can select
which kernel to run at boot, even have multiple root file systems
(production, backup) and swap between them.  It takes a lot of the risk
out of upgrades by providing a good escape route if networking fails to
come up properly, for example.  With the recent ARP fix, there was a
functional regression in the first version of the patch, which caused
routing to fail under some circumstances.  If you had access to a serial
console for a remote box, you were fine because you could revert to the
previous kernel once you noticed the problem.  Otherwise, you might be out
of luck...

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at      Network Associates Laboratories

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