libndr: Add ndr_pull_struct_blob_all_noalloc

This allows us to remove talloc() calls from GUID_from_ndr_blob().

To do this the struct ndr_pull is placed on the stack, and filled in there.

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

3 files changed, 44 insertions, 9 deletions

diff --git a/librpc/ndr/libndr.h b/librpc/ndr/libndr.h
index a268f128145..10054376eec 100644
--- a/librpc/ndr/libndr.h
+++ b/librpc/ndr/libndr.h
@@ -550,6 +550,8 @@ uint32_t ndr_print_get_switch_value(struct ndr_print *ndr, const void *p);
 uint32_t ndr_pull_steal_switch_value(struct ndr_pull *ndr, const void *p);
 enum ndr_err_code ndr_pull_struct_blob(const DATA_BLOB *blob, TALLOC_CTX *mem_ctx, void *p, ndr_pull_flags_fn_t fn);
 enum ndr_err_code ndr_pull_struct_blob_all(const DATA_BLOB *blob, TALLOC_CTX *mem_ctx, void *p, ndr_pull_flags_fn_t fn);
+enum ndr_err_code ndr_pull_struct_blob_all_noalloc(const DATA_BLOB *blob,
+						   void *p, ndr_pull_flags_fn_t fn);
 enum ndr_err_code ndr_pull_union_blob(const DATA_BLOB *blob, TALLOC_CTX *mem_ctx, void *p, uint32_t level, ndr_pull_flags_fn_t fn);
 enum ndr_err_code ndr_pull_union_blob_all(const DATA_BLOB *blob, TALLOC_CTX *mem_ctx, void *p, uint32_t level, ndr_pull_flags_fn_t fn);
 
diff --git a/librpc/ndr/ndr.c b/librpc/ndr/ndr.c
index 89bacf7de5f..f66029ab2cb 100644
--- a/librpc/ndr/ndr.c
+++ b/librpc/ndr/ndr.c
@@ -1161,6 +1161,45 @@ _PUBLIC_ enum ndr_err_code ndr_pull_struct_blob_all(const DATA_BLOB *blob, TALLO
 }
 
 /*
+  pull a struct from a blob using NDR - failing if all bytes are not consumed
+
+  This only works for structures with NO allocated memory, like
+  objectSID and GUID.  This helps because we parse these a lot.
+*/
+_PUBLIC_ enum ndr_err_code ndr_pull_struct_blob_all_noalloc(const DATA_BLOB *blob,
+							    void *p, ndr_pull_flags_fn_t fn)
+{
+	/*
+	 * We init this structure on the stack here, to avoid a
+	 * talloc() as otherwise this call to the fn() is assured not
+	 * to be doing any allocation, eg SIDs and GUIDs.
+	 *
+	 * This allows us to keep the safety of the PIDL-generated
+	 * code without the talloc() overhead.
+	 */
+	struct ndr_pull ndr = {
+		.data = blob->data,
+		.data_size = blob->length,
+		.current_mem_ctx = (void *)-1
+	};
+	uint32_t highest_ofs;
+	NDR_CHECK(fn(&ndr, NDR_SCALARS|NDR_BUFFERS, p));
+	if (ndr.offset > ndr.relative_highest_offset) {
+		highest_ofs = ndr.offset;
+	} else {
+		highest_ofs = ndr.relative_highest_offset;
+	}
+	if (highest_ofs < ndr.data_size) {
+		enum ndr_err_code ret;
+		ret = ndr_pull_error(&ndr, NDR_ERR_UNREAD_BYTES,
+				     "not all bytes consumed ofs[%u] size[%u]",
+				     highest_ofs, ndr.data_size);
+		return ret;
+	}
+	return NDR_ERR_SUCCESS;
+}
+
+/*
   pull a union from a blob using NDR, given the union discriminator
 */
 _PUBLIC_ enum ndr_err_code ndr_pull_union_blob(const DATA_BLOB *blob, TALLOC_CTX *mem_ctx, 
diff --git a/librpc/ndr/uuid.c b/librpc/ndr/uuid.c
index 654bebd0d08..9d955abc3d5 100644
--- a/librpc/ndr/uuid.c
+++ b/librpc/ndr/uuid.c
@@ -42,15 +42,9 @@ _PUBLIC_ NTSTATUS GUID_to_ndr_blob(const struct GUID *guid, TALLOC_CTX *mem_ctx,
 */
 _PUBLIC_ NTSTATUS GUID_from_ndr_blob(const DATA_BLOB *b, struct GUID *guid)
 {
-	enum ndr_err_code ndr_err;
-	TALLOC_CTX *mem_ctx;
-
-	mem_ctx = talloc_new(NULL);
-	NT_STATUS_HAVE_NO_MEMORY(mem_ctx);
-
-	ndr_err = ndr_pull_struct_blob_all(b, mem_ctx, guid,
-					   (ndr_pull_flags_fn_t)ndr_pull_GUID);
-	talloc_free(mem_ctx);
+	enum ndr_err_code ndr_err =
+		ndr_pull_struct_blob_all_noalloc(b, guid,
+						 (ndr_pull_flags_fn_t)ndr_pull_GUID);
 	return ndr_map_error2ntstatus(ndr_err);
 }