On 28/01/16 13:39, Christian Heimes wrote:
On 2016-01-28 13:51, Roderick Johnstone wrote:
Hi

My netapp filer is happily doing ldap over ssl lookups for account
information to my RHEL 6.7 testing ipa server
(ipa-server-3.0.0-47.el6_7.1.x86_64).

However, when I switch the filer to use my RHEL 7.2 ipa server
(ipa-server-4.2.0-15.el7_2.3.x86_64) the lookup doesn't work.

In the dirsrv log file I see entries like this:

[28/Jan/2016:09:17:45 +0000] conn=1338 fd=112 slot=112 SSL connection
from xxx.xxx.xxx.xxx to yyy.yyy.yy.yyy
[28/Jan/2016:09:17:45 +0000] conn=1338 op=-1 fd=112 closed - Cannot
communicate securely with peer: no common encryption algorithm(s).

(xxx.xxx.xxx.xxx is the filer ip address and yyy.yyy.yyy.yyy is the ipa
server ip address).

Looking in the ldap directory for fields with cipher in the name shows a
very different set of nssslenabledciphers between the two ipa-server
versions.

I wonder if this might be the issue?

Can the ldap server tell me what ciphers its being requested to use by
the filer?

Yes, it looks like it is the issue. The supported cipher suites were
hardened a while ago. The ticket
https://fedorahosted.org/freeipa/ticket/4395 contains more information.

During the TLS handshake the client sends a list of supported cipher
suites to the server. The server also has a list of supported cipher
suites. But the server never sends this list to the client. Instead it
picks one common cipher suite (usually the most secure) from the common
set of cipher suites.

I don't know if you can get 389 DS to print the cipher suites. But you
can snoop the ciper suites from the TLS handshake with wireshark or
tshark. The handshake isnt't encrypted and can be captures on either the
host or the server.

# tshark -Vx -Y "ssl.handshake.ciphersuites" -i YOUR_INTERFACE tcp port
ldaps

Christian


Thanks Christian. Thats really helpful.

Now I have a list of ciphers being asked for and I found that the ldap server logs which ciphers its using when it starts up file /var/log/dirsrv/slapd-<domain>/error. There isn't any overlap.

I noticed that there is a setting in the
dn: cn=encryption,cn=config
allowWeakCipher: off

and
nsSSL3Ciphers: +all

and found some documentation on this here: http://directory.fedoraproject.org/docs/389ds/design/nss-cipher-design.html

So, maybe I could add one (or several) of the required ciphers to nsSSL3Ciphers or possibly as a last resort set allowWeakCipher: on?

Roderick

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