Thursday, November 1, 2018

Proftpd builds broken on FreeBSD? Use gmake

I recently discovered an issue with our automated build of proftpd. I changed the target branch from the ancient 1.3.5 branch to 1.3.6. When I tried building this branch, I got a failure in the mod_sftp directory.

In file included from mod_sftp.c:29:
./mod_sftp.h:29:10: fatal error: 'conf.h' file not found
#include "conf.h"

After a bunch of screwing around and ripping my hair out, I took the time to actually read the INSTALL file. It turns out that GNU Make is required. We have been using BSD Make, so there must have been a recent-ish change that causes make to fail.

Tuesday, September 11, 2018

Pulling your hair out trying to fix your Mikrotik? Maybe your version of Netinstall is broken.

I spent an afternoon tearing my hair out. First, I managed to kinda-brick my Mikrotik during a firmware upgrade; the OS appeared to boot, but none of the network interfaces were visible, and it was generally disfunctional.

Reading up on the recovery process, I downloaded and installed the latest version of Netinstall, per the Mikrotik wiki. I spent the next four hours hating life, cursing technology, until I figured out the problem...the current version of Netinstall is broken!

If your copy of Netinstall just sits there, and your device never appears in the list, try this.

  1. Download and extract Netinstall version 6.38.7 (I was running 6.43).
  2. If you're using Windows 10 64-bit like me, open the properties for the executable. Change compatibility mode to Windows XP SP3, and run as Administrator (I'm not positive that either of these are required, but it's what I used).
  3. Run Netinstall.
  4. Device promptly appears.

Grrr.


Wednesday, August 22, 2018

sudo: ldap_start_tls_s(): Connect error

A quick hint for FreeBSD users of sudo that authorize via LDAP. If you're getting the following message when running sudo:

sudo: ldap_start_tls_s(): Connect error

associated with this error message in the logs:

sudo: in openpam_check_error_code(): pam_sm_authenticate(): unexpected return value 27

Check that your ldap.conf TLS parameters are correct! In my case, Ansible pushed a bunch of pending config changes (and an OS update) to a neglected host, one of which included moving the CA certificate file, but failed to update the ldap.conf file. I chased my tail for a bit, thinking the issue was with nslcd.conf.

You may also notice a corresponding error in the log of the LDAP server. In the case of slapd:

slapd[40731]: conn=4892528 fd=219 closed (TLS negotiation failure)

Monday, September 18, 2017

VMFS version confusion and FreeBSD UNMAP

I recently started moving VMWare guests to a new ESXi 6.5 host, when I experienced an unusual problem. Guests would get tied up in knots, endlessly sending the following error messages to the console.

(da0:mpt0:0:0:0): UNMAP. CDB: 42 00 00 00 00 00 00 02 68 00
(da0:mpt0:0:0:0): CAM status: SCSI Status Error
(da0:mpt0:0:0:0): SCSI status: Busy
(da0:mpt0:0:0:0): Retrying command

After a bunch of Google hits (mostly FreeNAS users) that didn't totally add up for me, I have a theory on the actual cause of the issue. In short, I think that this issue is caused by the presence of the following conditions.


  1.  VMWare vSphere 6.5 host, which supports both VMFS5 and VMFS6.
  2. A FreeBSD guest, using...
  3. A virtual disk that is thinly-provisioned, and stored on a VMFS5 filesystem.
VMFS6 supports the use of the UNMAP command, which allows the guest operating system to inform the hypervisor that it is no longer using a block. When the virtual disk is thin-provisioned, the host can reallocate the block to the pool of available disk space. FreeBSD has included support for this SCSI command for some time.

My theory is this. I think ESXi is lying to the guests. I think that when a thin guest is created on a VMFS5 filesystem, the UNMAP command is still exposed/permitted, even though the underlying filesystem doesn't actually support it. When the guest tries to send the UNMAP command, it gets a bogus response. In the case of FreeBSD, it retries the command perpetually, hanging up the system.

The search hits I found (linked above) mention switching the virtual disk to a SATA/IDE bus as a workaround. I suspect that this works because the UNMAP command does not exist on those buses, preventing the issue from occurring. I believe that the following solutions are less hacky. 

  1. When creating virtual disks for FreeBSD on VMFS5 filesystems, they should always be thick provisioned (I use eager zeroing, I haven't tested lazy). This seems to be the one-size-fits-all solution. It's also worth noting that the ESXi installer uses VMFS5 on the system disk, with no apparent way to use VMFS6.
  2. If you must use thin-provisioning, make sure that it is on a VMFS6 filesystem. I have not tested this extensively, but it seems to work.
  3. Thin-provisioned guests also seem to behave normally on NFS-backed storage.
In my testing, I have not had any issues on guests provisioned per #1.

Saturday, August 26, 2017

Display the listening ports on CentOS 7

It's been a while since I was serious about Linux, but the fun new goodies have lured me back towards the fold. A lot of things have changed over the last few years, some for the better, some not, but that's way beyond the scope here.

One thing that has been removed (at least from CentOS) is netstat. I'm going to call that a win, because invoking netstat always required a trip to the man page, aside from the trusty netstat -lnp.  The problem I have is that CentOS (and presumably RHEL) removed netstat, but decades worth of Google indexing has entrenched netstat as the blessed method of pulling a list of listening sockets.

Installing net-tools seems like the wrong approach, there must be a better way...and there is! Buried in a blog post, I found a conversion reference for netstat functionality. From this, I learned that ss is the replacement for the functionality I need. As an added bonus, it appears that the basic syntax is similar to my beloved sockstat.

For example, my oft-used "what's listening on the network":

ss -l46

Friday, August 12, 2016

Arcane Bourne shell behavior. The colon (:)

I finally learned the purpose of starting a command with the colon utility (:) in bourne shell. It expands any arguments, then exits 0. This is handy for hiding pointless error messages resulting from variable substitution. Consider the following example.

$ ${D:=foo}
foo: not found
$ echo $D
foo

The example above sets variable D to "foo" if it is unset or null. It works fine, but causes the annoying error 'foo: not found'. We can suppress that message with the colon.

$ unset D
$ : ${D:=foo}
$ echo $D

foo

Much prettier!

Also see:
Parameter Expansion (and explanation of the colon utility at the bottom of the page)

Thursday, March 3, 2016

LDAP password hashing in PHP, a better way

Reviewing some PHP code related to user password changes, I noticed that the code was using unsalted SHA-1 hashes to store the password in LDAP. This is potentially very bad, if an attacker were able to gain access to the password hashes, because pre-computed rainbow tables for unsalted SHA-1 are pretty common. This has been the basis for a number of high-profile data breaches in recent memory, and I don't want to be on the news.

Looking for a better solution on Google, I quickly discovered the source of the bad code, the OpenLDAP FAQ-o-matic. In this FAQ entry, there are code examples for a variety of languages, many offering higher security. However, the PHP example included only a SHA-1 variant, and was copy-pasted nearly verbatim into my subject code (I wonder how many other web applications have done this very thing).

OpenLDAP has support for a variety of different hashing algorithms, including an optional SHA-2 module, and passthrough to the OpenSSL crypto(3) library. The strongest native cipher supported by OpenLDAP is salted-SHA1 (SSHA), which allows sufficient strength for this application, when used with a decently-large salt. I wrote the following function to generate such hashes from PHP, provided here in hopes that people will quit using unsalted SHA in their web-apps.

/*
 * This is a helper function, returning a Salted SHA-1 hash, suitable for LDAP.
 * OpenLDAP uses a slightly strange scheme for generating these hashes, but it's
 * far better than unsalted SHA. The only limit on salt length appears to be the
 * maximum length of the userPassword attribute in LDAP (128), allowing us to
 * safely use a 64-byte salt, resulting in a 118-byte SSHA. For the curious,
 * this works out to:
 *
 *   6B ({SSHA} tag) + 28B (20B SHA, B64 encoded) + 88B (64B salt, B64 encoded)
 *
 */

function generate_ssha_hash($cleartext)
{

        /*
         * Generate a unique 64-byte salt value for the salt.
         *
         * Use mcrypt_create_iv to generate some random bytes. PHP 7 has a
         * random_bytes() function, and the OpenSSL extension provides
         * openssl_random_pseudo_bytes(), which may be better, but this
         * should work
         */
        $pw_salt = mcrypt_create_iv(64, MCRYPT_DEV_URANDOM);

        // Concatenate and hash password+salt.
        $hashed = sha1($cleartext . $pw_salt, TRUE);

        // Add the tag and encoded hash+salt.
        $hashed = '{SSHA}' . base64_encode($hashed . $pw_salt);

        // Clean up
        unset($pw_salt);

        return $hashed;


} // generate_ssha_hash