From 863a0a7badf3919c4a710df67e98dbf5db0a2690 Mon Sep 17 00:00:00 2001
From: David Benjamin <davidben@google.com>
Date: Tue, 20 Dec 2022 10:36:19 -0500
Subject: [PATCH] gh-100372: Use BIO_eof to detect EOF for SSL_FILETYPE_ASN1

In PEM, we need to parse until error and then suppress
PEM_R_NO_START_LINE, because PEM allows arbitrary leading and trailing
data. DER, however, does not. Parsing until error and suppressing
ASN1_R_HEADER_TOO_LONG doesn't quite work because that error also
covers some cases that should be rejected.

Instead, check BIO_eof early and stop the loop that way.
---
 Lib/test/test_ssl.py                                                    |    2 ++
 Misc/NEWS.d/next/Library/2022-12-20-10-55-14.gh-issue-100372.utfP65.rst |    2 ++
 Modules/_ssl.c                                                          |   10 ++++++----
 3 files changed, 10 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-12-20-10-55-14.gh-issue-100372.utfP65.rst

Index: Python-3.6.15/Lib/test/test_ssl.py
===================================================================
--- Python-3.6.15.orig/Lib/test/test_ssl.py
+++ Python-3.6.15/Lib/test/test_ssl.py
@@ -1209,6 +1209,8 @@ class ContextTests(unittest.TestCase):
             "not enough data: cadata does not contain a certificate"
         ):
             ctx.load_verify_locations(cadata=b"broken")
+        with self.assertRaises(ssl.SSLError):
+            ctx.load_verify_locations(cadata=cacert_der + b"A")
 
 
     def test_load_dh_params(self):
Index: Python-3.6.15/Misc/NEWS.d/next/Library/2022-12-20-10-55-14.gh-issue-100372.utfP65.rst
===================================================================
--- /dev/null
+++ Python-3.6.15/Misc/NEWS.d/next/Library/2022-12-20-10-55-14.gh-issue-100372.utfP65.rst
@@ -0,0 +1,2 @@
+:meth:`ssl.SSLContext.load_verify_locations` no longer incorrectly accepts
+some cases of trailing data when parsing DER.
Index: Python-3.6.15/Modules/_ssl.c
===================================================================
--- Python-3.6.15.orig/Modules/_ssl.c
+++ Python-3.6.15/Modules/_ssl.c
@@ -3579,7 +3579,7 @@ _add_ca_certs(PySSLContext *self, void *
 {
     BIO *biobuf = NULL;
     X509_STORE *store;
-    int retval = -1, err, loaded = 0;
+    int retval = -1, err, loaded = 0, was_bio_eof = 0;
 
     assert(filetype == SSL_FILETYPE_ASN1 || filetype == SSL_FILETYPE_PEM);
 
@@ -3607,6 +3607,10 @@ _add_ca_certs(PySSLContext *self, void *
         int r;
 
         if (filetype == SSL_FILETYPE_ASN1) {
+            if (BIO_eof(biobuf)) {
+                was_bio_eof = 1;
+                break;
+            }
             cert = d2i_X509_bio(biobuf, NULL);
         } else {
             cert = PEM_read_bio_X509(biobuf, NULL,
@@ -3642,9 +3646,7 @@ _add_ca_certs(PySSLContext *self, void *
         }
         _setSSLError(msg, 0, __FILE__, __LINE__);
         retval = -1;
-    } else if ((filetype == SSL_FILETYPE_ASN1) &&
-                    (ERR_GET_LIB(err) == ERR_LIB_ASN1) &&
-                    (ERR_GET_REASON(err) == ASN1_R_HEADER_TOO_LONG)) {
+    } else if ((filetype == SSL_FILETYPE_ASN1) && was_bio_eof) {
         /* EOF ASN1 file, not an error */
         ERR_clear_error();
         retval = 0;