[Freeipa-users] Ghost ipaSshPubKey in sss_ssh_authorizedkeys or 'Error looking up public keys'

Tue Jun 21 07:43:44 UTC 2016

On Mon, Jun 20, 2016 at 10:46:13PM +0200, Martin Štefany wrote:
> Hello all,
> 
> I've ran into strange issue with IPA/SSSD/SSH/SELinux which started when I
> figured out that I cannot ssh with pubkey auth to Fedora 23 (ipa-client) systems
> while I can to CentOS 7.2 (ipa-client and ipa-server) systems within same IPA
> domain. I will appreciate any help whatsoever.
> IPA servers (and most of the clients) are IPA 4.2.0 on CentOS 7.2 with latest
> updates, affected clients are IPA clients 4.2.4 on Fedora 23 with latest
> updates.
> 
> I started by looking to the journal:
> jún 20 13:02:50 desk2.stefany.eu sshd[25162]: Connection
> from 144.xxx.xxx.xxx port 22543 on 172.17.100.191 port 22
> ...
> jún 20 13:02:56 desk2.stefany.eu audit[23328]: AVC avc:  denied  { name_connect
> } for  pid=23328 comm="sssd_ssh" dest=80 scontext=system_u:system_r:sssd_t:s0
> tcontext=system_u:object_r:http_port_t:s0 tclass=tcp_socket permissive=0
> jún 20 13:02:56 desk2.stefany.eu audit[23328]: SYSCALL arch=c000003e syscall=42
> success=no exit=-13 a0=15 a1=7fff145c35b0 a2=10 a3=5614dbbe2a50 items=0
> ppid=23316 pid=23328 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0
> sgid=0 

Does the user by chance have a certificate added to his entry including
a link to an OCSP responder?

Recent version of SSSD have the ability to generate public ssh-keys from
valid certificates added to the user entry to support the ssh Smartcard
feature (see e.g. the -I option in the ssh man page for details or
https://fedorahosted.org/sssd/wiki/DesignDocs/SmartcardAuthenticationStep1#RunningsshclientwithSmartcardsupport)

While trying to validate thecertificate via OCSP sssd_ssh must connect
to a http server. To allow this setting the 'nis_enabled' SELinux
boolean to true should help.

Nevertheless, since this should work by default, it would be nice if you
can open a bugzilla ticket for the SELinux policy on F23 to allow this
by default.

HTH

bye,
Sumit

> ...
> jún 20 13:02:56 desk2.stefany.eu audit[23328]: AVC avc:  denied  { name_connect
> } for  pid=23328 comm="sssd_ssh" dest=80 scontext=system_u:system_r:sssd_t:s0
> tcontext=system_u:object_r:http_port_t:s0 tclass=tcp_socket permissive=0
> jún 20 13:02:56 desk2.stefany.eu audit[23328]: SYSCALL arch=c000003e syscall=42
> success=no exit=-13 a0=15 a1=7fff145c35b0 a2=10 a3=5614dbbe42d0 items=0
> ppid=23316 pid=23328 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0
> sgid=0 
> ...
> jún 20 13:02:56 desk2.stefany.eu sshd[25162]: error: AuthorizedKeysCommand
> /usr/bin/sss_ssh_authorizedkeys martin failed, status 1
> ...
> jún 20 13:02:56 desk2.stefany.eu sshd[25162]: Failed publickey for martin
> from 144.xxx.xxx.xxx port 22543 ssh2: RSA SHA256:uyzB4[stripped]
> ...
> jún 20 13:02:56 desk2.stefany.eu sshd[25162]: error: Received disconnect
> from 144.xxx.xxx.xxx port 22543:14: No supported authentication methods
> available [preauth]
> jún 20 13:02:56 desk2.stefany.eu sshd[25162]: Disconnected from 144.xxx.xxx.xxx
> port 22543 [preauth]
> 
> which was weird, because the same key would nicely work elsewhere (on any other
> CentOS 7.2 system, while no Fedora 23 system would work as I have figured out)
> 
> I have tried putting SELinux into permissive mode, or generating custom module
> with custom policy allowing this, but it doesn't help, and even tcpdump capture
> doesn't capture anything when such connection to 'somewhere' port 80 is opened.
> 
> I moved on to testing the '/usr/bin/sss_ssh_authorizedkeys martin' command.
> Fedora 23:
> # sss_ssh_authorizedkeys martin
> Error looking up public keys
> 
> CentOS 7.2:
> # sss_ssh_authorizedkeys martin
> ssh-rsa AAA...
> ssh-rsa AAA...
> ssh-ed25519 AAA...
> ssh-rsa AAA...
> ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCsox... (???) -->> this is one is not in
> LDAP (checked with ldapsearch & ipa user-show martin --all --raw), not present
> in dc=stefany,dc=eu tree or in compat tree
> 
> So, I have turned on debug_level = 0x0250 in sssd.conf in both Fedora 23 and
> CentOS 7.2 and checked the logs. CentOS 7.2 is just fine, Fedora 23 gives these
> failures:
> ==> /var/log/sssd/sssd_ssh.log <==
> (Mon Jun 20 21:58:14 2016) [sssd[ssh]] [sss_cmd_get_version] (0x0200): Received
> client version [0].
> (Mon Jun 20 21:58:14 2016) [sssd[ssh]] [sss_cmd_get_version] (0x0200): Offered
> version [0].
> (Mon Jun 20 21:58:14 2016) [sssd[ssh]] [sss_parse_name_for_domains] (0x0200):
> name 'martin' matched without domain, user is martin
> 
> ==> /var/log/sssd/sssd_stefany.eu.log <==
> (Mon Jun 20 21:58:14 2016) [sssd[be[stefany.eu]]] [be_get_account_info]
> (0x0200): Got request for [0x1][BE_REQ_USER][1][name=martin]
> 
> ==> /var/log/sssd/sssd_ssh.log <==
> (Mon Jun 20 21:58:14 2016) [sssd[ssh]] [decode_and_add_base64_data] (0x0040):
> cert_to_ssh_key failed.
> (Mon Jun 20 21:58:14 2016) [sssd[ssh]] [ssh_cmd_build_reply] (0x0040):
> decode_and_add_base64_data failed.
> 
> And that's right, the last - ghost - "sshpubkey" is invalid base64 string. So
> Fedora 23 fails because of some extra validation in SSSD...
> 
> I can't tell where this invalid base64 stuff is coming from, and yes, I have
> stopped both IPA servers, run sss_cache -E on both of them and on clients, and
> started IPA servers serially one by one, the invalid key is still there.
> 
> I have a plan B to delete the account, put it back and see if it cleans up, but
> I would prefer to figure out what is actually wrong here and what's introducing
> the wrong sshpubkey. And why is sssd_ssh connecting to some port 80 somewhere
> 
> Thank you in advance!
> 
> Kind regards,
> Martin
> 
> 
> 
> 
> 

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