[PATCH] libsemanage: treat module data as bytes in the Python bindings

semanage_module_install() / semanage_module_install_info() take a
(char *data, size_t data_len) pair, and semanage_module_extract()
returns (void **mapped_data, size_t *data_len). In both directions
the payload is an opaque module blob (.pp / bzip2 / CIL / HLL), not a
NUL-terminated C string.

On Python 3 the current SWIG bindings get this wrong on both sides:

- install()/install_info(): the SWIG default for a bare "char *"
  only accepts str objects and UTF-8-encodes them, so a .pp blob
  cannot be passed at all, and even for CIL text the separately
  supplied data_len is wrong for any non-ASCII content since
  Python len(str) counts code points, not UTF-8 bytes.

- extract(): %cstring_output_allocate_size turns the mapped buffer
  into a str via UTF-8 decoding, which for a binary module either
  raises UnicodeDecodeError or (with surrogateescape) yields a str
  that cannot be fed straight back into install().

Add a (char *module_data, size_t data_len) input typemap that
accepts any object exposing the buffer protocol (bytes, bytearray,
mmap, ...) as a single argument and derives the length from it, and
apply it to the (char *data, size_t data_len) pair of
semanage_module_install_info() as well.

Replace the extract() output typemap with an explicit multi-argument
typemap that returns a bytes object built from the mapped buffer and
then unmaps it, so extract() -> install() round-trips.  Drop the
now-unused <cstring.i> include.

The Python signatures become
  semanage_module_install(sh, data, name, ext_lang)
  semanage_module_install_info(sh, modinfo, data)
There are no in-tree Python callers.

Fixes: https://github.com/SELinuxProject/selinux/issues/502
Signed-off-by: Stephen Smalley <[email protected]>
---
 libsemanage/src/semanageswig_python.i | 43 +++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/libsemanage/src/semanageswig_python.i b/libsemanage/src/semanageswig_python.i
index 0ca09763..1729e965 100644
--- a/libsemanage/src/semanageswig_python.i
+++ b/libsemanage/src/semanageswig_python.i
@@ -102,9 +102,46 @@
 %apply int *OUTPUT { unsigned int * };
 %apply int *OUTPUT { uint16_t * };
 
-%include <cstring.i>
-/* This is needed to properly mmap binary data in SWIG */
-%cstring_output_allocate_size(void **mapped_data, size_t *data_len, munmap(*$1, *$2));
+/*
+ * semanage_module_extract(): the (void **mapped_data, size_t *data_len) pair
+ * is an opaque module blob (.pp / bzip2 / CIL / HLL).  Return it to Python
+ * as a bytes object; %cstring_output_allocate_size would UTF-8-decode it
+ * into a str, which corrupts binary modules.
+ */
+%typemap(in, numinputs=0) (void **mapped_data, size_t *data_len)
+	(void *temp_data = NULL, size_t temp_len = 0) {
+	$1 = &temp_data;
+	$2 = &temp_len;
+}
+%typemap(argout) (void **mapped_data, size_t *data_len) {
+	if (*$1) {
+		$result = SWIG_AppendOutput(
+			$result,
+			PyBytes_FromStringAndSize((const char *)*$1, *$2));
+		munmap(*$1, *$2);
+	} else {
+		$result = SWIG_AppendOutput($result, SWIG_Py_Void());
+	}
+}
+
+/*
+ * semanage_module_install() and semanage_module_install_info() take a
+ * (char *data, size_t data_len) pair that is an opaque module blob
+ * (.pp / bzip2 / CIL / HLL), not a NUL-terminated C string.  Accept any
+ * Python object exposing the buffer protocol (bytes, bytearray, mmap, ...)
+ * as a single argument and derive the length from it.
+ */
+%typemap(in) (char *module_data, size_t data_len) (Py_buffer view) {
+	view.obj = NULL;
+	if (PyObject_GetBuffer($input, &view, PyBUF_SIMPLE) < 0)
+		SWIG_fail;
+	$1 = (char *)view.buf;
+	$2 = (size_t)view.len;
+}
+%typemap(freearg) (char *module_data, size_t data_len) {
+	PyBuffer_Release(&view$argnum);
+}
+%apply (char *module_data, size_t data_len) { (char *data, size_t data_len) };
 
 %typemap(in, numinputs=0) char **(char *temp=NULL) {
 	$1 = &temp;
-- 
2.55.0