gh-118209: Add structured exception handling to mmap module

Misc/NEWS.d/next/Windows/2024-04-24-05-16-32.gh-issue-118209.Ryyzlz.rst

@@ -0,0 +1 @@
+Fix crash in :func:`mmap.read` on Windows when the underlying file operation raises errors.

Modules/mmapmodule.c

@@ -255,6 +255,44 @@ do {                                                                    \
 } while (0)
 #endif /* UNIX */
 
+#if defined(MS_WIN32) && !defined(DONT_USE_SEH)
+static DWORD
+filter_page_exception(EXCEPTION_POINTERS *ptrs, EXCEPTION_RECORD *record)
+{
+    *record = *ptrs->ExceptionRecord;
+    if (ptrs->ExceptionRecord->ExceptionCode == EXCEPTION_IN_PAGE_ERROR) {
+        return EXCEPTION_EXECUTE_HANDLER;
+    }
+    return EXCEPTION_CONTINUE_SEARCH;
+}
+#endif
+
+int
+safe_memcpy(void *restrict dest, const void *restrict src, size_t count) {
+#if defined(MS_WIN32) && !defined(DONT_USE_SEH)
+
+    // never fail for count 0
+    if (count == 0) {
+        return 0;
+    }
+
+    EXCEPTION_RECORD record;
+    __try {
+        memcpy(dest, src, count);
+        return 0;
+    }
+    __except (filter_page_exception(GetExceptionInformation(), &record)) {
+        NTSTATUS status = record.ExceptionInformation[2];
+        ULONG code = LsaNtStatusToWinError(status);
+        PyErr_SetFromWindowsErr(code);
+        return -1;
+    }
+#else
+    memcpy(dest, src, count);
+    return 0;
+#endif
+}
+
 static PyObject *
 mmap_read_byte_method(mmap_object *self,
                       PyObject *Py_UNUSED(ignored))
@@ -264,7 +302,14 @@ mmap_read_byte_method(mmap_object *self,
         PyErr_SetString(PyExc_ValueError, "read byte out of range");
         return NULL;
     }
-    return PyLong_FromLong((unsigned char)self->data[self->pos++]);
+    unsigned char dest;
+    if (safe_memcpy(dest, self->data + self->pos, 1) < 0) {
+        return NULL;
+    }
+    else {
+        self->pos++;
+        return PyLong_FromLong(dest);
+    }
 }
 
 static PyObject *
@@ -307,8 +352,17 @@ mmap_read_method(mmap_object *self,
     remaining = (self->pos < self->size) ? self->size - self->pos : 0;
     if (num_bytes < 0 || num_bytes > remaining)
         num_bytes = remaining;
-    result = PyBytes_FromStringAndSize(&self->data[self->pos], num_bytes);
-    self->pos += num_bytes;
+
+    result = PyBytes_FromStringAndSize(NULL, num_bytes);
+    if (result == NULL) {
+        return NULL;
+    }
+    if (safe_memcpy(((PyBytesObject *) result)->ob_sval, self->data + self->pos, num_bytes) < 0) {
+        Py_CLEAR(result);
+    }
+    else {
+        self->pos += num_bytes;
+    }
     return result;
 }