UTIL: krb5 principal (un)marshalling

The KCM responder needs to read the contents of the principal blob that
the Kerberos library sends. Since libkrb5 doesn't export any API to do
so, we need to implement marshalling and unmarshalling of the principal
ourselves.

In future, when the KCM server also supports renewals, we will also need
to unmarshall the credentials, but until that is not really needed, the
credentials will be stored as a blob.

Reviewed-by: Michal Židek <mzidek@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>

2 files changed, 204 insertions, 0 deletions

diff --git a/src/util/sss_krb5.c b/src/util/sss_krb5.c
index 4808a7703..d461cf881 100644
--- a/src/util/sss_krb5.c
+++ b/src/util/sss_krb5.c
@@ -24,6 +24,7 @@
 
 #include "config.h"
 
+#include "util/sss_iobuf.h"
 #include "util/util.h"
 #include "util/sss_krb5.h"
 
@@ -1128,3 +1129,197 @@ done:
 
     return res;
 }
+
+static errno_t iobuf_read_uint32be(struct sss_iobuf *iobuf,
+                                   uint32_t *_val)
+{
+    uint32_t beval;
+    errno_t ret;
+
+    ret = sss_iobuf_read_uint32(iobuf, &beval);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    *_val = be32toh(beval);
+    return EOK;
+}
+
+static errno_t iobuf_write_uint32be(struct sss_iobuf *iobuf,
+                                    uint32_t val)
+{
+    uint32_t beval;
+
+    beval = htobe32(val);
+    return sss_iobuf_write_uint32(iobuf, beval);
+}
+
+static errno_t iobuf_get_len_bytes(TALLOC_CTX *mem_ctx,
+                                   struct sss_iobuf *iobuf,
+                                   uint32_t *_nbytes,
+                                   uint8_t **_bytes)
+{
+    errno_t ret;
+    uint32_t nbytes;
+    uint8_t *bytes = NULL;
+
+    ret = iobuf_read_uint32be(iobuf, &nbytes);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    bytes = talloc_zero_size(mem_ctx, nbytes);
+    if (bytes == NULL) {
+        return ENOMEM;
+    }
+
+    ret = sss_iobuf_read_len(iobuf, nbytes, bytes);
+    if (ret != EOK) {
+        talloc_free(bytes);
+        return ret;
+    }
+
+    *_bytes = bytes;
+    *_nbytes = nbytes;
+    return EOK;
+}
+
+static errno_t get_krb5_data(TALLOC_CTX *mem_ctx,
+                             struct sss_iobuf *iobuf,
+                             krb5_data *k5data)
+{
+    errno_t ret;
+    uint32_t nbytes;
+    uint8_t *bytes = NULL;
+
+    ret = iobuf_get_len_bytes(mem_ctx, iobuf,  &nbytes, &bytes);
+    if (ret != EOK) {
+        talloc_free(bytes);
+        return ret;
+    }
+
+    k5data->data = (char *) bytes; /* FIXME - the cast is ugly */
+    k5data->length = nbytes;
+    return EOK;
+}
+
+static errno_t set_krb5_data(struct sss_iobuf *iobuf,
+                             krb5_data *k5data)
+{
+    errno_t ret;
+
+    ret = iobuf_write_uint32be(iobuf, k5data->length);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    if (k5data->length > 0) {
+        ret = sss_iobuf_write_len(iobuf,
+                                  (uint8_t *) k5data->data,
+                                  k5data->length);
+        if (ret != EOK) {
+            return ret;
+        }
+    }
+
+    return EOK;
+}
+
+/* FIXME - it would be nice if Kerberos exported these APIs.. */
+krb5_error_code sss_krb5_unmarshal_princ(TALLOC_CTX *mem_ctx,
+                                         struct sss_iobuf *iobuf,
+                                         krb5_principal *_princ)
+{
+    krb5_principal princ = NULL;
+    krb5_error_code ret;
+    uint32_t ncomps;
+
+    if (iobuf == NULL || _princ == NULL) {
+        return EINVAL;
+    }
+
+    princ = talloc_zero(mem_ctx, struct krb5_principal_data);
+    if (princ == NULL) {
+        return ENOMEM;
+    }
+
+    princ->magic = KV5M_PRINCIPAL;
+
+    ret = iobuf_read_uint32be(iobuf, (uint32_t *) &princ->type);
+    if (ret != EOK) {
+        goto fail;
+    }
+
+    ret = iobuf_read_uint32be(iobuf, &ncomps);
+    if (ret != EOK) {
+        goto fail;
+    }
+
+    if (ncomps > sss_iobuf_get_capacity(iobuf)) {
+        /* Sanity check to avoid large allocations */
+        ret = EINVAL;
+        goto fail;
+    }
+
+    if (ncomps != 0) {
+        princ->data = talloc_zero_array(princ, krb5_data, ncomps);
+        if (princ->data == NULL) {
+            ret = ENOMEM;
+            goto fail;
+        }
+
+        princ->length = ncomps;
+    }
+
+    ret = get_krb5_data(princ, iobuf, &princ->realm);
+    if (ret != EOK) {
+        goto fail;
+    }
+
+    for (size_t i = 0; i < ncomps; i++) {
+        ret = get_krb5_data(princ->data, iobuf, &princ->data[i]);
+        if (ret != EOK) {
+            goto fail;
+        }
+    }
+
+    *_princ = princ;
+    return 0;
+
+fail:
+    talloc_free(princ);
+    return ret;
+}
+
+krb5_error_code sss_krb5_marshal_princ(krb5_principal princ,
+                                       struct sss_iobuf *iobuf)
+{
+    krb5_error_code ret;
+
+    if (iobuf == NULL || princ == NULL) {
+        return EINVAL;
+    }
+
+    ret = iobuf_write_uint32be(iobuf, princ->type);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    ret = iobuf_write_uint32be(iobuf, princ->length);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    ret = set_krb5_data(iobuf, &princ->realm);
+    if (ret != EOK) {
+        return ret;
+    }
+
+    for (int i = 0; i < princ->length; i++) {
+        ret = set_krb5_data(iobuf, &princ->data[i]);
+        if (ret != EOK) {
+            return ret;
+        }
+    }
+    return EOK;
+}
diff --git a/src/util/sss_krb5.h b/src/util/sss_krb5.h
index ac0f6082c..0d9043be9 100644
--- a/src/util/sss_krb5.h
+++ b/src/util/sss_krb5.h
@@ -32,6 +32,7 @@
 #include <krb5.h>
 #endif
 
+#include "util/sss_iobuf.h"
 #include "util/util.h"
 
 #define KRB5_CHILD_LOG_FILE     "krb5_child"
@@ -186,4 +187,12 @@ krb5_error_code sss_krb5_kt_have_content(krb5_context context,
                                          krb5_keytab keytab);
 
 bool sss_krb5_realm_has_proxy(const char *realm);
+
+krb5_error_code sss_krb5_marshal_princ(krb5_principal princ,
+                                       struct sss_iobuf *iobuf);
+
+krb5_error_code sss_krb5_unmarshal_princ(TALLOC_CTX *mem_ctx,
+                                         struct sss_iobuf *iobuf,
+                                         krb5_principal *_princ);
+
 #endif /* __SSS_KRB5_H__ */