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s3:librpc/gse: make use of gss_krb5_import_cred() instead of gss_acquire_cred()

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This avoids the usage of the ccselect_realm logic in MIT krb5,
which leads to unpredictable results.

The problem is the usage of gss_acquire_cred(), that just creates
a credential handle without ccache.

As result gss_init_sec_context() will trigger a code path
where it use "ccselect" plugins. And the ccselect_realm
module just chooses a random ccache from a global list
where the realm of the provides target principal matches
the realm of the ccache user principal.

In the winbindd case we're using MEMORY:cliconnect to setup
the smb connection to the DC. For ldap connections we use
MEMORY:winbind_ccache.

The typical case is that we do the smb connection first.
If we try to create a new ldap connection, while the
credentials in MEMORY:cliconnect are expired,
we'll do the required kinit into MEMORY:winbind_ccache,
but the ccselect_realm module will select MEMORY:cliconnect
and tries to get a service ticket for the ldap server
using the already expired TGT from MEMORY:cliconnect.

The solution will be to use gss_krb5_import_cred() and explicitly
pass the desired ccache, which avoids the ccselect logic.

We could also use gss_acquire_cred_from(), but that's only available
in modern MIT krb5 versions, while gss_krb5_import_cred() is available
in heimdal and all supported MIT versions (>=1.9).
As far as I can see both call the same internal function in MIT
(at least for the ccache case).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12480

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit 7c3ea9fe96336483752adb821f8062a883d52998)
This commit is contained in:
Stefan Metzmacher 2016-12-22 08:49:38 +01:00
parent 838be147f0
commit e7fbca8a48
1 changed files with 18 additions and 13 deletions
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31
source3/librpc/crypto/gse.c
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@ -203,7 +203,6 @@ static NTSTATUS gse_init_client(TALLOC_CTX *mem_ctx,
struct gse_context *gse_ctx;
OM_uint32 gss_maj, gss_min;
gss_buffer_desc name_buffer = GSS_C_EMPTY_BUFFER;
gss_OID_set_desc mech_set;
#ifdef HAVE_GSS_KRB5_CRED_NO_CI_FLAGS_X
gss_buffer_desc empty_buffer = GSS_C_EMPTY_BUFFER;
#endif
@ -248,20 +247,26 @@ static NTSTATUS gse_init_client(TALLOC_CTX *mem_ctx,
/* TODO: get krb5 ticket using username/password, if no valid
* one already available in ccache */
mech_set.count = 1;
mech_set.elements = &gse_ctx->gss_mech;
gss_maj = gss_acquire_cred(&gss_min,
GSS_C_NO_NAME,
GSS_C_INDEFINITE,
&mech_set,
GSS_C_INITIATE,
&gse_ctx->creds,
NULL, NULL);
gss_maj = gss_krb5_import_cred(&gss_min,
gse_ctx->ccache,
NULL, /* keytab_principal */
NULL, /* keytab */
&gse_ctx->creds);
if (gss_maj) {
DEBUG(5, ("gss_acquire_creds failed for GSS_C_NO_NAME with [%s] -"
char *ccache = NULL;
int kret;
kret = krb5_cc_get_full_name(gse_ctx->k5ctx,
gse_ctx->ccache,
&ccache);
if (kret != 0) {
ccache = NULL;
}
DEBUG(5, ("gss_krb5_import_cred ccache[%s] failed with [%s] -"
"the caller may retry after a kinit.\n",
gse_errstr(gse_ctx, gss_maj, gss_min)));
ccache, gse_errstr(gse_ctx, gss_maj, gss_min)));
SAFE_FREE(ccache);
status = NT_STATUS_INTERNAL_ERROR;
goto err_out;
}