KCM: sss_iobuf_init_empty() shall not zero memory

sss_iobuf_init_empty() and related functions zero the allocated memory
even though it is not needed. Most of the time, all the fields in the
structures will be set to non-zero values. In these cases zeroing the
is useless and we stop doing it.

Only in two cases, some pointers were being left unmodified, so they
are now being manually set to NULL.

Resolves: SSSD#7014

src/responder/kcm/kcmsrv_ccache.c

@@ -233,7 +233,6 @@ struct kcm_cred *kcm_cred_new(TALLOC_CTX *mem_ctx,
     if (kcreds == NULL) {
         return NULL;
     }
-
     uuid_copy(kcreds->uuid, uuid);
     kcreds->cred_blob = talloc_steal(kcreds, cred_blob);
     return kcreds;

src/util/sss_iobuf.c

@@ -18,6 +18,7 @@ struct sss_iobuf {
     size_t capacity;        /* Maximum capacity */
 };
 
+/* The allocated buffer (iobuf->data) will not be zeroed. */
 struct sss_iobuf *sss_iobuf_init_empty(TALLOC_CTX *mem_ctx,
                                        size_t size,
                                        size_t capacity)
@@ -30,7 +31,7 @@ struct sss_iobuf *sss_iobuf_init_empty(TALLOC_CTX *mem_ctx,
         return NULL;
     }
 
-    buf = talloc_zero_array(iobuf, uint8_t, size);
+    buf = talloc_array(iobuf, uint8_t, size);
     if (buf == NULL) {
         talloc_free(iobuf);
         return NULL;
@@ -43,11 +44,12 @@ struct sss_iobuf *sss_iobuf_init_empty(TALLOC_CTX *mem_ctx,
     iobuf->data = buf;
     iobuf->size = size;
     iobuf->capacity = capacity;
-    iobuf->dp = 0;
 
     return iobuf;
 }
 
+/* The allocated buffer (iobuf->data) will not be zeroed
+ * if data is not provided. */
 struct sss_iobuf *sss_iobuf_init_readonly(TALLOC_CTX *mem_ctx,
                                           const uint8_t *data,
                                           size_t size)
@@ -80,7 +82,6 @@ struct sss_iobuf *sss_iobuf_init_steal(TALLOC_CTX *mem_ctx,
     iobuf->data = talloc_steal(iobuf, data);
     iobuf->size = size;
     iobuf->capacity = size;
-    iobuf->dp = 0;
 
     return iobuf;
 }