Fix i2v_GENERAL_NAME to not assume NUL terminated strings

ASN.1 strings may not be NUL terminated. Don't assume they are.

CVE-2021-3712

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>

crypto/x509v3/v3_alt.c

@@ -9,6 +9,7 @@
 
 #include <stdio.h>
 #include "internal/cryptlib.h"
+#include "crypto/x509.h"
 #include <openssl/conf.h>
 #include <openssl/x509v3.h>
 #include "ext_dat.h"
@@ -99,17 +100,20 @@ STACK_OF(CONF_VALUE) *i2v_GENERAL_NAME(X509V3_EXT_METHOD *method,
         break;
 
     case GEN_EMAIL:
-        if (!X509V3_add_value_uchar("email", gen->d.ia5->data, &ret))
+        if (!x509v3_add_len_value_uchar("email", gen->d.ia5->data,
+                                        gen->d.ia5->length, &ret))
             return NULL;
         break;
 
     case GEN_DNS:
-        if (!X509V3_add_value_uchar("DNS", gen->d.ia5->data, &ret))
+        if (!x509v3_add_len_value_uchar("DNS", gen->d.ia5->data,
+                                        gen->d.ia5->length, &ret))
             return NULL;
         break;
 
     case GEN_URI:
-        if (!X509V3_add_value_uchar("URI", gen->d.ia5->data, &ret))
+        if (!x509v3_add_len_value_uchar("URI", gen->d.ia5->data,
+                                        gen->d.ia5->length, &ret))
             return NULL;
         break;
 

crypto/x509v3/v3_utl.c

@@ -12,6 +12,7 @@
 #include "e_os.h"
 #include "internal/cryptlib.h"
 #include <stdio.h>
+#include <string.h>
 #include "crypto/ctype.h"
 #include <openssl/conf.h>
 #include <openssl/crypto.h>
@@ -34,17 +35,26 @@ static int ipv6_hex(unsigned char *out, const char *in, int inlen);
 
 /* Add a CONF_VALUE name value pair to stack */
 
-int X509V3_add_value(const char *name, const char *value,
-                     STACK_OF(CONF_VALUE) **extlist)
+static int x509v3_add_len_value(const char *name, const char *value,
+                                size_t vallen, STACK_OF(CONF_VALUE) **extlist)
 {
     CONF_VALUE *vtmp = NULL;
     char *tname = NULL, *tvalue = NULL;
     int sk_allocated = (*extlist == NULL);
 
-    if (name && (tname = OPENSSL_strdup(name)) == NULL)
-        goto err;
-    if (value && (tvalue = OPENSSL_strdup(value)) == NULL)
+    if (name != NULL && (tname = OPENSSL_strdup(name)) == NULL)
         goto err;
+    if (value != NULL && vallen > 0) {
+        /*
+         * We tolerate a single trailing NUL character, but otherwise no
+         * embedded NULs
+         */
+        if (memchr(value, 0, vallen - 1) != NULL)
+            goto err;
+        tvalue = OPENSSL_strndup(value, vallen);
+        if (tvalue == NULL)
+            goto err;
+    }
     if ((vtmp = OPENSSL_malloc(sizeof(*vtmp))) == NULL)
         goto err;
     if (sk_allocated && (*extlist = sk_CONF_VALUE_new_null()) == NULL)
@@ -67,10 +77,26 @@ int X509V3_add_value(const char *name, const char *value,
     return 0;
 }
 
+int X509V3_add_value(const char *name, const char *value,
+                     STACK_OF(CONF_VALUE) **extlist)
+{
+    return x509v3_add_len_value(name, value,
+                                value != NULL ? strlen((const char *)value) : 0,
+                                extlist);
+}
+
 int X509V3_add_value_uchar(const char *name, const unsigned char *value,
                            STACK_OF(CONF_VALUE) **extlist)
 {
-    return X509V3_add_value(name, (const char *)value, extlist);
+    return x509v3_add_len_value(name, (const char *)value,
+                                value != NULL ? strlen((const char *)value) : 0,
+                                extlist);
+}
+
+int x509v3_add_len_value_uchar(const char *name, const unsigned char *value,
+                               size_t vallen, STACK_OF(CONF_VALUE) **extlist)
+{
+    return x509v3_add_len_value(name, (const char *)value, vallen, extlist);
 }
 
 /* Free function for STACK_OF(CONF_VALUE) */

include/crypto/x509.h

@@ -8,6 +8,8 @@
  */
 
 #include "internal/refcount.h"
+#include <openssl/x509.h>
+#include <openssl/conf.h>
 
 /* Internal X509 structures and functions: not for application use */
 
@@ -284,3 +286,6 @@ int a2i_ipadd(unsigned char *ipout, const char *ipasc);
 int x509_set1_time(ASN1_TIME **ptm, const ASN1_TIME *tm);
 
 void x509_init_sig_info(X509 *x);
+
+int x509v3_add_len_value_uchar(const char *name, const unsigned char *value,
+                               size_t vallen, STACK_OF(CONF_VALUE) **extlist);