Change X509_NAME_get_index_by[NID|OBJ] to be safer.

Currently these functions return raw ASN1_STRING bytes as
a C string and ignore the encoding in a "hold my beer I am
a toolkit not a functioning API surely it's just for testing
and you'd never send nasty bytes" kind of way.

Sadly some callers seem to use them to fetch things liks
subject name components for comparisons, and often just
use the result as a C string.

Instead, encode the resulting bytes as UTF-8 so it is
something like "text",

Add a failure case if the length provided is inadequate
or if the resulting text would contain an nul byte.

based on boringssl.

nits by dlg@
ok tb@

2 files changed, 47 insertions, 20 deletions

diff --git a/src/lib/libcrypto/man/X509_NAME_get_index_by_NID.3 b/src/lib/libcrypto/man/X509_NAME_get_index_by_NID.3
index 71dd98ce46..19a123a4ac 100644
--- a/src/lib/libcrypto/man/X509_NAME_get_index_by_NID.3
+++ b/src/lib/libcrypto/man/X509_NAME_get_index_by_NID.3
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: X509_NAME_get_index_by_NID.3,v 1.13 2022/07/02 17:09:09 jsing Exp $
+.\"     $OpenBSD: X509_NAME_get_index_by_NID.3,v 1.14 2023/05/02 14:13:05 beck Exp $
 .\"     OpenSSL aebb9aac Jul 19 09:27:53 2016 -0400
 .\"
 .\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
@@ -49,7 +49,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 .\" OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: July 2 2022 $
+.Dd $Mdocdate: May 2 2023 $
 .Dt X509_NAME_GET_INDEX_BY_NID 3
 .Os
 .Sh NAME
@@ -136,22 +136,32 @@ run from 0 to
 .Fn X509_NAME_get_text_by_NID
 and
 .Fn X509_NAME_get_text_by_OBJ
-retrieve the "text" from the first entry in
+retrieve the bytes encoded as UTF-8 from the first entry in
 .Fa name
 which matches
 .Fa nid
 or
 .Fa obj .
-At most
-.Fa len
-bytes will be written and the text written to
-.Fa buf
-will be NUL terminated.
 If
 .Fa buf
 is
 .Dv NULL ,
 nothing is written, but the return value is calculated as usual.
+If
+.Fa buf
+is not
+.Dv NULL ,
+no more than
+.Fa len
+bytes will be written and the text written to
+.Fa buf
+will be NUL terminated.
+.Pp
+Nothing is written and it is a failure if
+.Fa len
+is not large enough to hold the NUL byte terminated UTF-8 encoding of
+the text, or if the UTF-8 encoding ot the text would contins a NUL
+byte.
 .Pp
 All relevant
 .Dv NID_*
@@ -189,8 +199,8 @@ if the index is invalid.
 .Fn X509_NAME_get_text_by_NID
 and
 .Fn X509_NAME_get_text_by_OBJ
-return the length of the output string written, not counting the
-terminating NUL, or -1 if no match is found.
+return the length of the output UTF-8 string written, not counting the
+terminating NUL, or -1 in the case of an error or no match being found.
 .Pp
 In some cases of failure of
 .Fn X509_NAME_get_index_by_NID
diff --git a/src/lib/libcrypto/x509/x509name.c b/src/lib/libcrypto/x509/x509name.c
index a6e4dbef89..3c9e224c1b 100644
--- a/src/lib/libcrypto/x509/x509name.c
+++ b/src/lib/libcrypto/x509/x509name.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: x509name.c,v 1.31 2023/02/16 08:38:17 tb Exp $ */
+/* $OpenBSD: x509name.c,v 1.32 2023/05/02 14:13:05 beck Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -66,6 +66,7 @@
 #include <openssl/stack.h>
 #include <openssl/x509.h>
 
+#include "bytestring.h"
 #include "x509_local.h"
 
 int
@@ -84,21 +85,37 @@ int
 X509_NAME_get_text_by_OBJ(X509_NAME *name, const ASN1_OBJECT *obj, char *buf,
     int len)
 {
-        int i;
+        unsigned char *text = NULL;
         ASN1_STRING *data;
+        int i, text_len;
+        int ret = -1;
+        CBS cbs;
 
         i = X509_NAME_get_index_by_OBJ(name, obj, -1);
         if (i < 0)
-                return (-1);
+                goto err;
         data = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(name, i));
-        i = (data->length > (len - 1)) ? (len - 1) : data->length;
-        if (buf == NULL)
-                return (data->length);
-        if (i >= 0) {
-                memcpy(buf, data->data, i);
-                buf[i] = '\0';
+        /*
+         * Fail if we cannot encode as UTF-8, or if the UTF-8 encoding of the
+         * string contains a 0 byte, because mortal callers seldom handle the
+         * length difference correctly
+         */
+        if ((text_len = ASN1_STRING_to_UTF8(&text, data)) < 0)
+                goto err;
+        CBS_init(&cbs, text, text_len);
+        if (CBS_contains_zero_byte(&cbs))
+                goto err;
+        /* We still support the "pass NULL to find out how much" API */
+        if (buf != NULL) {
+                if (!CBS_write_bytes(&cbs, buf, len - 1, NULL))
+                        goto err;
+                /* It must be a C string */
+                buf[text_len] = '\0';
         }
-        return (i);
+        ret = text_len;
+ err:
+        free(text);
+        return (ret);
 }
 LCRYPTO_ALIAS(X509_NAME_get_text_by_OBJ);