[SSSD] [PATCH] Send error message from krb5_child to backend.

Ondrej Kos okos at redhat.com
Thu Jun 13 15:51:18 UTC 2013


On 06/13/2013 05:37 PM, Jakub Hrozek wrote:
> On Thu, Jun 13, 2013 at 04:40:43PM +0200, Ondrej Kos wrote:
>> On 06/12/2013 05:51 PM, Jakub Hrozek wrote:
>>> On Fri, May 24, 2013 at 04:52:49PM +0200, Lukas Slebodnik wrote:
>>>> ehlo,
>>>>
>>>> Commit c6872e79e8496fd075e20aec0343ade99cca725c caused that password migration
>>>> doesn't work using sssd.
>>>>
>>>> If pre authentication failed then we should send message to backend,
>>>> so password migration could be detected.
>>>>
>>>> https://fedorahosted.org/sssd/ticket/1873
>>>>
>>>> Patch is attached.
>>>>
>>>> LS
>>>
>>> Hi,
>>>
>>> sorry the review took such a long time. However, this is not the correct
>>> approach. If you take a look at ipa_auth.c and how the migration is
>>> performed in src/providers/ipa/ipa_auth.c:
>>>
>>> 263     if (state->pd->cmd == SSS_PAM_AUTHENTICATE &&
>>> 264         state->pd->pam_status == PAM_CRED_ERR) {
>>> 265
>>> 266         req = get_password_migration_flag_send(state, state->ev,
>>>
>>> The migration is attempted if the krb5_auth request returns PAM_CRED_ERR
>>> as the PAM error. Now the PAM error is converted from an error code the
>>> Kerberos child process sends to the krb5_auth request in
>>> krb5_auth_done().
>>>
>>> When a user is migrated from LDAP then the authentication would fail
>>> with KRB5_PREAUTH_FAILED in the krb5_child process and the krb5_child
>>> would return ERR_AUTH_FAILED (see src/providers/krb5/krb5_child.c:1201).
>>>
>>> ERR_AUTH_FAILED is then converted in krb5_auth_done() into PAM_AUTH_ERR.
>>>
>>> So I see two options here:
>>>      1) change the condition in ipa_auth.c from detecting PAM_CRED_ERR to
>>>      detecting PAM_AUTH_ERR. I don't like this because any authentication
>>>      failure would then check the migration flag.
>>>      2) Add a new ERR_AUTH code, maybe ERR_PREAUTH_FAILED to krb5_child,
>>>      return that instead of ERR_AUTH_FAILED from the krb5_child and
>>>      convert ERR_PREAUTH_FAILED into PAM_CRED_ERR in krb5_auth_done.
>>>
>>> BTW to prove this was indeed the root cause, I tested by implementing 1)
>>> option above:
>>>
>>> diff --git a/src/providers/ipa/ipa_auth.c b/src/providers/ipa/ipa_auth.c
>>> index 651196a..03576eb 100644
>>> --- a/src/providers/ipa/ipa_auth.c
>>> +++ b/src/providers/ipa/ipa_auth.c
>>> @@ -261,7 +261,7 @@ static void ipa_auth_handler_done(struct tevent_req *req)
>>>       }
>>>
>>>       if (state->pd->cmd == SSS_PAM_AUTHENTICATE &&
>>> -        state->pd->pam_status == PAM_CRED_ERR) {
>>> +        state->pd->pam_status == PAM_AUTH_ERR) {
>>>
>>>           req = get_password_migration_flag_send(state, state->ev,
>>>                                                state->ipa_auth_ctx->sdap_id_ctx,
>>>
>>> And the migration worked like a charm.
>>> _______________________________________________
>>> sssd-devel mailing list
>>> sssd-devel at lists.fedorahosted.org
>>> https://lists.fedorahosted.org/mailman/listinfo/sssd-devel
>>>
>>
>> Hi,
>>
>> Attached is a patch witch fixes this issue correctly, following Jakub's
>> second provided option.
>>
>
> The patch works fine, thank you. Some comments about the error code
> below:
>
>> --- a/src/providers/krb5/krb5_auth.c
>> +++ b/src/providers/krb5/krb5_auth.c
>> @@ -1032,8 +1032,8 @@ static void krb5_auth_done(struct tevent_req *subreq)
>>           ret = EOK;
>>           goto done;
>>
>> -    case ERR_AUTH_FAILED:
>> -        state->pam_status = PAM_AUTH_ERR;
>> +    case ERR_PREAUTH_FAILED:
>> +        state->pam_status = PAM_CRED_ERR;
>>           state->dp_err = DP_ERR_OK;
>
> we want to keep both cases here, ERR_AUTH_FAILED is still returned if
> authentication fails with wrong password.
>
>>           ret = EOK;
>>           goto done;
>> diff --git a/src/providers/krb5/krb5_child.c b/src/providers/krb5/krb5_child.c
>> index 8f746a8db561928349ffed8b7434db2a113a1f86..dc1f06dd1e86954ca1f4c90e97d9eb95022e07fd 100644
>> --- a/src/providers/krb5/krb5_child.c
>> +++ b/src/providers/krb5/krb5_child.c
>> @@ -1174,7 +1174,7 @@ static errno_t map_krb5_error(krb5_error_code kerr)
>>       case KRB5KRB_AP_ERR_BAD_INTEGRITY:
>
> BAD_INTEGRITY should still return AUTH_FAILED.
>
>>       case KRB5_PREAUTH_FAILED:
>>       case KRB5KDC_ERR_PREAUTH_FAILED:
>> -        return ERR_AUTH_FAILED;
>> +        return ERR_PREAUTH_FAILED;
>>
>>       default:
>>           return ERR_INTERNAL;
>> diff --git a/src/util/util_errors.c b/src/util/util_errors.c
>> index b617f540691a245d1132469a1f019bcb0eb6e775..096ac532fc7b9c8deb025ef9e948bc04ed0e0959 100644
>> --- a/src/util/util_errors.c
>> +++ b/src/util/util_errors.c
>> @@ -35,6 +35,7 @@ struct err_string error_to_str[] = {
>>       { "Cached credentials are expired" }, /* ERR_CACHED_CREDS_EXPIRED */
>>       { "Authentication Denied" }, /* ERR_AUTH_DENIED */
>>       { "Authentication Failed" }, /* ERR_AUTH_FAILED */
>
> I know I suggested ERR_PREAUTH_FAILED but now I'm thinking it might not
> be the best code, because it's too Kerberos specific. So what about
> using more generic ERR_CRED_INVALID ?
>
>> +    { "Preauthentication Failed"}, /* ERR_PREAUTH_FAILED */
>>       { "Password Change Denied" }, /* ERR_CHPASS_DENIED */
>>       { "Password Change Failed" }, /* ERR_CHPASS_FAILED */
>>       { "Network I/O Error" }, /* ERR_NETWORK_IO */
>> diff --git a/src/util/util_errors.h b/src/util/util_errors.h
>> index a602a6ea92f72a51f5e21342940b2072bbe9296d..2143774c3a2113e5ad372aa97770220c4cf3f859 100644
>> --- a/src/util/util_errors.h
>> +++ b/src/util/util_errors.h
>> @@ -57,6 +57,7 @@ enum sssd_errors {
>>       ERR_CACHED_CREDS_EXPIRED,
>>       ERR_AUTH_DENIED,
>>       ERR_AUTH_FAILED,
>> +    ERR_PREAUTH_FAILED,
>
> The new error code would have to be updated here, too.
>
>>       ERR_CHPASS_DENIED,
>>       ERR_CHPASS_FAILED,
>>       ERR_NETWORK_IO,
>> --
>> 1.8.1.4
>>
> _______________________________________________
> sssd-devel mailing list
> sssd-devel at lists.fedorahosted.org
> https://lists.fedorahosted.org/mailman/listinfo/sssd-devel
>

Thanks for hints, new patch is attached.

Ondra

-- 
Ondrej Kos
Associate Software Engineer
Identity Management - SSSD
Red Hat Czech
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