bpo-41894: Fix UnicodeDecodeError while loading native module (GH-22466)

When running in a non-UTF-8 locale, if an error occurs while importing a
native Python module (say because a dependent share library is missing),
the error message string returned may contain non-ASCII code points
causing a UnicodeDecodeError.

PyUnicode_DecodeFSDefault is used for buffers which may contain
filesystem  paths. For consistency with os.strerror(),
PyUnicode_DecodeLocale is used for buffers which contain system error
messages. While the shortname parameter is always encoded in ASCII
according to PEP 489, it is left decoded using PyUnicode_FromString to
minimize the changes and since it should not affect the decoding (albeit
_potentially_ slower).

In dynload_hpux, since the error buffer contains a message generated
from a static ASCII string and the module filesystem path,
PyUnicode_DecodeFSDefault is used instead of PyUnicode_DecodeLocale as
is used elsewhere.

* bpo-41894: Fix bugs in dynload error msg handling

For both dynload_aix and dynload_hpux, properly handle the possibility
that decoding strings may return NULL and when such an error happens,
properly decrement any previously decoded strings and return early.

In addition, in dynload_aix, ensure that we pass the decoded string
*object* pathname_ob to PyErr_SetImportError instead of the original
pathname buffer.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/Python/dynload_aix.c b/Python/dynload_aix.c
index 684f10a..97f7698 100644
--- a/Python/dynload_aix.c
+++ b/Python/dynload_aix.c
@@ -144,10 +144,16 @@ aix_loaderror(const char *pathname)
         ERRBUF_APPEND(message[i]);
         ERRBUF_APPEND("\n");
     }
-    errbuf[strlen(errbuf)-1] = '\0';            /* trim off last newline */
-    pathname_ob = PyUnicode_FromString(pathname);
-    errbuf_ob = PyUnicode_FromString(errbuf);
-    PyErr_SetImportError(errbuf_ob, NULL, pathname);
+    /* Subtract 1 from the length to trim off trailing newline */
+    errbuf_ob = PyUnicode_DecodeLocaleAndSize(errbuf, strlen(errbuf)-1, "surrogateescape");
+    if (errbuf_ob == NULL)
+        return;
+    pathname_ob = PyUnicode_DecodeFSDefault(pathname);
+    if (pathname_ob == NULL) {
+        Py_DECREF(errbuf_ob);
+        return;
+    }
+    PyErr_SetImportError(errbuf_ob, NULL, pathname_ob);
     Py_DECREF(pathname_ob);
     Py_DECREF(errbuf_ob);
     return;