asn1basic: add missing test from BoringSSL's test suite

This is another test that fails due to the bug in i2c_ASN1_BIT_STRING().

1 files changed, 32 insertions, 1 deletions

diff --git a/src/regress/lib/libcrypto/asn1/asn1basic.c b/src/regress/lib/libcrypto/asn1/asn1basic.c
index e6df6559f5..0666e5b061 100644
--- a/src/regress/lib/libcrypto/asn1/asn1basic.c
+++ b/src/regress/lib/libcrypto/asn1/asn1basic.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: asn1basic.c,v 1.19 2026/01/04 09:42:32 tb Exp $ */
+/* $OpenBSD: asn1basic.c,v 1.20 2026/01/04 09:43:52 tb Exp $ */
 /*
  * Copyright (c) 2017, 2021 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2021 Google, Inc
@@ -237,6 +237,8 @@ static const uint8_t asn1_bit_string_10010[] = {
         0x03, 0x02, 0x03, 0x90,
 };
 
+static const uint8_t asn1_bit_string_zeroes[64] = { 0 };
+
 static int
 asn1_bit_string_set_bit_test(void)
 {
@@ -625,6 +627,35 @@ asn1_bit_string_set_bit_test(void)
             asn1_bit_string_1001, sizeof(asn1_bit_string_1001)))
                 goto failed;
 
+        /*
+         * ASN1_BIT_STRING_set() also truncates
+         */
+
+        ASN1_BIT_STRING_free(abs);
+        abs = NULL;
+
+        if ((abs = ASN1_BIT_STRING_new()) == NULL) {
+                fprintf(stderr, "FAIL: ASN1_BIT_STRING_new\n");
+                goto failed;
+        }
+
+        if (!ASN1_STRING_set(abs, asn1_bit_string_zeroes,
+            sizeof(asn1_bit_string_zeroes))) {
+                fprintf(stderr, "FAIL: ASN1_BIT_STRING_set zeroes\n");
+                goto failed;
+        }
+
+        freezero(der, der_len);
+        der = NULL;
+        if ((der_len = i2d_ASN1_BIT_STRING(abs, &der)) <= 0) {
+                fprintf(stderr, "FAIL: i2d_ASN1_BIT_STRING\n");
+                der_len = 0;
+                goto failed;
+        }
+        if (!asn1_compare_bytes("BIT STRING all zeroes", der, der_len,
+            asn1_bit_string_empty, sizeof(asn1_bit_string_empty)))
+                goto failed;
+
         failed = 0;
 
  failed: