librpc: Add ndr_push_struct_into_fixed_blob() and use it in GUID_to_ndr_blob()

This allows us to allocate only the correct size, not a default of 1024 bytes
per push.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>

3 files changed, 51 insertions, 3 deletions

diff --git a/librpc/ndr/libndr.h b/librpc/ndr/libndr.h
index 6034229336e..0c3c55a9bf2 100644
--- a/librpc/ndr/libndr.h
+++ b/librpc/ndr/libndr.h
@@ -83,7 +83,8 @@ struct ndr_push {
 	uint8_t *data;
 	uint32_t alloc_size;
 	uint32_t offset;
-
+	bool fixed_buf_size;
+	
 	uint32_t relative_base_offset;
 	uint32_t relative_end_offset;
 	struct ndr_token_list *relative_base_list;
@@ -466,6 +467,9 @@ bool ndr_syntax_id_equal(const struct ndr_syntax_id *i1, const struct ndr_syntax
 char *ndr_syntax_id_to_string(TALLOC_CTX *mem_ctx, const struct ndr_syntax_id *id);
 bool ndr_syntax_id_from_string(const char *s, struct ndr_syntax_id *id);
 enum ndr_err_code ndr_push_struct_blob(DATA_BLOB *blob, TALLOC_CTX *mem_ctx, const void *p, ndr_push_flags_fn_t fn);
+enum ndr_err_code ndr_push_struct_into_fixed_blob(DATA_BLOB *blob,
+						  const void *p,
+						  ndr_push_flags_fn_t fn);
 enum ndr_err_code ndr_push_union_blob(DATA_BLOB *blob, TALLOC_CTX *mem_ctx, void *p, uint32_t level, ndr_push_flags_fn_t fn);
 size_t ndr_size_struct(const void *p, int flags, ndr_push_flags_fn_t push);
 size_t ndr_size_union(const void *p, int flags, uint32_t level, ndr_push_flags_fn_t push);
diff --git a/librpc/ndr/ndr.c b/librpc/ndr/ndr.c
index 78cde20f7d1..22c4d763d09 100644
--- a/librpc/ndr/ndr.c
+++ b/librpc/ndr/ndr.c
@@ -254,6 +254,17 @@ _PUBLIC_ enum ndr_err_code ndr_push_expand(struct ndr_push *ndr, uint32_t extra_
 				      size);
 	}
 
+	if (ndr->fixed_buf_size) {
+		if (ndr->alloc_size >= size) {
+			return NDR_ERR_SUCCESS;
+		}
+		return ndr_push_error(ndr,
+				      NDR_ERR_BUFSIZE,
+				      "Overflow of fixed buffer in "
+				      "push_expand to %u",
+				      size);
+	}
+	
 	if (ndr->alloc_size > size) {
 		return NDR_ERR_SUCCESS;
 	}
@@ -1264,6 +1275,35 @@ _PUBLIC_ enum ndr_err_code ndr_push_struct_blob(DATA_BLOB *blob, TALLOC_CTX *mem
 	return NDR_ERR_SUCCESS;
 }
 
+/* 
+  push a struct into a provided blob using NDR. 
+ 
+  We error because we want to have the performance issue (extra
+  talloc() calls) show up as an error, not just slower code.  This is
+  used for things like GUIDs, which we expect to be a fixed size, and
+  SIDs that we can pre-calculate the size for.
+*/
+_PUBLIC_ enum ndr_err_code ndr_push_struct_into_fixed_blob(
+	DATA_BLOB *blob, const void *p, ndr_push_flags_fn_t fn)
+{
+	struct ndr_push ndr = {
+		.data = blob->data,
+		.alloc_size = blob->length,
+		.fixed_buf_size = true
+	};
+
+	NDR_CHECK(fn(&ndr, NDR_SCALARS|NDR_BUFFERS, p));
+
+	if (ndr.offset != blob->length) {
+		return ndr_push_error(&ndr, NDR_ERR_BUFSIZE,
+				      "buffer was either to large or small "
+				      "ofs[%u] size[%zu]",
+				      ndr.offset, blob->length);
+	}
+
+	return NDR_ERR_SUCCESS;
+}
+
 /*
   push a union to a blob using NDR
 */
diff --git a/librpc/ndr/uuid.c b/librpc/ndr/uuid.c
index fbd305e5401..a3f68d1d344 100644
--- a/librpc/ndr/uuid.c
+++ b/librpc/ndr/uuid.c
@@ -31,8 +31,12 @@
 _PUBLIC_ NTSTATUS GUID_to_ndr_blob(const struct GUID *guid, TALLOC_CTX *mem_ctx, DATA_BLOB *b)
 {
 	enum ndr_err_code ndr_err;
-	ndr_err = ndr_push_struct_blob(b, mem_ctx, guid,
-				       (ndr_push_flags_fn_t)ndr_push_GUID);
+	*b = data_blob_talloc(mem_ctx, NULL, 16);
+	if (b->data == NULL) {
+		return NT_STATUS_NO_MEMORY;
+	}
+	ndr_err = ndr_push_struct_into_fixed_blob(
+		b, guid, (ndr_push_flags_fn_t)ndr_push_GUID);
 	return ndr_map_error2ntstatus(ndr_err);
 }