--- lib/libpam/modules/pam_krb5/pam_krb5.8.orig +++ lib/libpam/modules/pam_krb5/pam_krb5.8 @@ -108,6 +108,21 @@ .Ql %p , to designate the current process ID; can be used in .Ar name . +.It Cm allow_kdc_spoof +Allow +.Nm +to succeed even if there is no host or service key available in a +keytab to authenticate the Kerberos KDC's ticket. +If there is no such key, for example on a host with no keytabs, +.Nm +will fail immediately without prompting the user. +.Pp +.Sy Warning : +If the host has not been configured with a keytab from the KDC, setting +this option makes it vulnerable to malicious KDCs, e.g. via DNS +flooding, because +.Nm +has no way to distinguish the legitimate KDC from a spoofed KDC. .It Cm no_user_check Do not verify if a user exists on the local system. This option implies the .Cm no_ccache --- lib/libpam/modules/pam_krb5/pam_krb5.c.orig +++ lib/libpam/modules/pam_krb5/pam_krb5.c @@ -76,7 +76,12 @@ #define COMPAT_HEIMDAL /* #define COMPAT_MIT */ -static int verify_krb_v5_tgt(krb5_context, krb5_ccache, char *, int); +static int verify_krb_v5_tgt_begin(krb5_context, char *, int, + const char **, krb5_principal *, char[static BUFSIZ]); +static int verify_krb_v5_tgt(krb5_context, krb5_ccache, char *, int, + const char *, krb5_principal, char[static BUFSIZ]); +static void verify_krb_v5_tgt_cleanup(krb5_context, int, + const char *, krb5_principal, char[static BUFSIZ]); static void cleanup_cache(pam_handle_t *, void *, int); static const char *compat_princ_component(krb5_context, krb5_principal, int); static void compat_free_data_contents(krb5_context, krb5_data *); @@ -92,6 +97,7 @@ #define PAM_OPT_NO_USER_CHECK "no_user_check" #define PAM_OPT_REUSE_CCACHE "reuse_ccache" #define PAM_OPT_NO_USER_CHECK "no_user_check" +#define PAM_OPT_ALLOW_KDC_SPOOF "allow_kdc_spoof" #define PAM_LOG_KRB5_ERR(ctx, rv, fmt, ...) \ do { \ @@ -109,6 +115,10 @@ { krb5_error_code krbret; krb5_context pam_context; + int debug; + const char *auth_service; + krb5_principal auth_princ; + char auth_phost[BUFSIZ]; krb5_creds creds; krb5_principal princ; krb5_ccache ccache; @@ -139,14 +149,37 @@ PAM_LOG("Got service: %s", (const char *)service); + if ((srvdup = strdup(service)) == NULL) { + retval = PAM_BUF_ERR; + goto cleanup6; + } + krbret = krb5_init_context(&pam_context); if (krbret != 0) { PAM_VERBOSE_ERROR("Kerberos 5 error"); - return (PAM_SERVICE_ERR); + retval = PAM_SERVICE_ERR; + goto cleanup5; } PAM_LOG("Context initialised"); + debug = openpam_get_option(pamh, PAM_OPT_DEBUG) ? 1 : 0; + krbret = verify_krb_v5_tgt_begin(pam_context, srvdup, debug, + &auth_service, &auth_princ, auth_phost); + if (krbret != 0) { /* failed to find key */ + /* Keytab or service key does not exist */ + /* + * Give up now because we can't authenticate the KDC + * with a keytab, unless the administrator asked to + * have the traditional behaviour of being vulnerable + * to spoofed KDCs. + */ + if (!openpam_get_option(pamh, PAM_OPT_ALLOW_KDC_SPOOF)) { + retval = PAM_SERVICE_ERR; + goto cleanup4; + } + } + krbret = krb5_cc_register(pam_context, &krb5_mcc_ops, FALSE); if (krbret != 0 && krbret != KRB5_CC_TYPE_EXISTS) { PAM_VERBOSE_ERROR("Kerberos 5 error"); @@ -292,13 +325,11 @@ PAM_LOG("Credentials stashed"); /* Verify them */ - if ((srvdup = strdup(service)) == NULL) { - retval = PAM_BUF_ERR; - goto cleanup; - } krbret = verify_krb_v5_tgt(pam_context, ccache, srvdup, - openpam_get_option(pamh, PAM_OPT_DEBUG) ? 1 : 0); + debug, + auth_service, auth_princ, auth_phost); free(srvdup); + srvdup = NULL; if (krbret == -1) { PAM_VERBOSE_ERROR("Kerberos 5 error"); krb5_cc_destroy(pam_context, ccache); @@ -349,8 +380,20 @@ PAM_LOG("Done cleanup3"); +cleanup4: + verify_krb_v5_tgt_cleanup(pam_context, debug, + auth_service, auth_princ, auth_phost); + PAM_LOG("Done cleanup4"); + +cleanup5: + if (srvdup != NULL) + free(srvdup); + PAM_LOG("Done cleanup5"); + +cleanup6: if (retval != PAM_SUCCESS) PAM_VERBOSE_ERROR("Kerberos 5 refuses you"); + PAM_LOG("Done cleanup6"); return (retval); } @@ -837,18 +880,18 @@ */ /* ARGSUSED */ static int -verify_krb_v5_tgt(krb5_context context, krb5_ccache ccache, - char *pam_service, int debug) +verify_krb_v5_tgt_begin(krb5_context context, char *pam_service, int debug, + const char **servicep, krb5_principal *princp __unused, char phost[static BUFSIZ]) { krb5_error_code retval; krb5_principal princ; krb5_keyblock *keyblock; - krb5_data packet; - krb5_auth_context auth_context; - char phost[BUFSIZ]; const char *services[3], **service; - packet.data = 0; + *servicep = NULL; + + if (debug) + openlog("pam_krb5", LOG_PID, LOG_AUTHPRIV); /* If possible we want to try and verify the ticket we have * received against a keytab. We will try multiple service @@ -906,14 +949,30 @@ krb5_free_error_message(context, msg); } retval = 0; - goto cleanup; } if (keyblock) krb5_free_keyblock(context, keyblock); + return (retval); +} + +static int +verify_krb_v5_tgt(krb5_context context, krb5_ccache ccache, + char *pam_service __unused, int debug, + const char *service, krb5_principal princ, char phost[static BUFSIZ]) +{ + krb5_error_code retval; + krb5_auth_context auth_context = NULL; + krb5_data packet; + + if (service == NULL) + return (0); /* uncertain, can't authenticate KDC */ + + packet.data = 0; + /* Talk to the kdc and construct the ticket. */ auth_context = NULL; - retval = krb5_mk_req(context, &auth_context, 0, *service, phost, + retval = krb5_mk_req(context, &auth_context, 0, service, phost, NULL, ccache, &packet); if (auth_context) { krb5_auth_con_free(context, auth_context); @@ -952,8 +1011,19 @@ cleanup: if (packet.data) compat_free_data_contents(context, &packet); - krb5_free_principal(context, princ); - return retval; + return (retval); +} + +static void +verify_krb_v5_tgt_cleanup(krb5_context context, int debug, + const char *service, krb5_principal princ, char phost[static BUFSIZ] __unused) +{ + + if (service) + krb5_free_principal(context, princ); + if (debug) + closelog(); + } /* Free the memory for cache_name. Called by pam_end() */