On Срд, 26 лют 2025, Spike White via sssd-users wrote:
Alexey,
if you look in /etc/ssh/sshd_config, there's numerous directives concerning
GSSAPI auth.
# GSSAPI options
GSSAPIAuthentication yes
GSSAPICleanupCredentials yes
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no
#GSSAPIEnablek5users no
So sshd knows natively about GSSAPI auth. Don't think it's using any PAM
stack for GSSAPI (auth phase).
When GSSAPI authentication is used against a service, the service
doesn't get access to the user's TGT unless it is explicitly delegated
by a client. The latter is not done by default. So when SSH server
authenticates the client with GSSAPI, by default it does not need to
have access to any credentials cache because it has nothing to save
there. This explains why it doesn't need to access KCM:.
Surely using PAM stack for account and session phases however.
Spike
On Wed, Feb 26, 2025 at 10:30 AM Alexey Tikhonov <[email protected]>
wrote:
Hi,
On Wed, Feb 26, 2025 at 5:07 PM Spike White via sssd-users
<[email protected]> wrote:
>
> We notice that when sssd-kcm service is messed up and not running,
password auth fails. Interestingly, Kerberos (GSSAPI auth still succeeds.
Why?
>
> So I know why password auth fails. In
/etc/krb5.conf.d/kcm_default_cache, it has:
>
> [libdefaults]
> default_ccache_name = KCM:
>
> So in password auth, it is failing on the step of writing the Kerberos
credential cache into the credentials store (KCM). I speculate that it’s
specifically pam_sss.so in the auth phase that’s failing to do this.
'krb5_child' (invoked by 'sssd_be' by request from 'sssd_pam' by
request from 'pam_sss.so') fails to store TGT.
> I understand why password auth fails. My question is – why does
Kerberos (GSSAPI) auth succeed?
>
> My guess is that sshd handles GSSAPI auth internally and never calls the
PAM stack in the “auth” phase. Only for the “account” and “session”
phase. Thus pam_sss.so never gets invoked for the auth phase.
I don't know if sshd uses 'pam_sss_gss.so', but that way or another, I
guess there is no need to acquire and store TGT on user behalf.
--
/ Alexander Bokovoy
Sr. Principal Software Engineer
Security / Identity Management Engineering
Red Hat Limited, Finland
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