[w3m-dev 02743] RFC2818 server identity check

From: Fumitoshi UKAI  <ukai@debian.or.jp>

ChangeLog

@@ -1,3 +1,17 @@
+2001-12-26  Fumitoshi UKAI  <ukai@debian.or.jp>
+
+	* [w3m-dev 02743] RFC2818 server identity check
+	* NEWS: RFC2818 server identity check
+	* istream.c (ssl_check_cert_ident): added
+	* istream.h (ssl_check_cert_ident): ditto
+	* istream.h: #include <x509v3.h>
+	* url.c (free_ssl_ctx): ssl_ctx = NULL
+	* url.c (openSSLHandle): arg hostname to check cert id
+	* url.c (openSSLHandle): check SSL_get_verify_result 
+			if ssl_verify_server
+	* url.c (openSSLHandle): check server identity by ssl_check_cert_ident
+	* url.c (openURL): openSSLHandle with pu->host
+
 2001-12-26  Hironori Sakamoto <hsaka@mth.biglobe.ne.jp>
 
 	* [w3m-dev 02715] bugfix in scripts/multipart/multipart.cgi.in
@@ -1599,4 +1613,4 @@
 	* release-0-2-1
 	* import w3m-0.2.1
 
-$Id: ChangeLog,v 1.178 2001/12/26 01:57:19 ukai Exp $
+$Id: ChangeLog,v 1.179 2001/12/26 12:18:06 ukai Exp $

NEWS

@@ -1,5 +1,6 @@
 w3m 0.2.4? 0.3?
 
+* RFC2818 server identity check
 * incremental search (C-s, C-r)
 * linux/ia64 support (?)
 

istream.c

@@ -1,4 +1,4 @@
-/* $Id: istream.c,v 1.6 2001/11/24 02:01:26 ukai Exp $ */
+/* $Id: istream.c,v 1.7 2001/12/26 12:18:06 ukai Exp $ */
 #include "fm.h"
 #include "istream.h"
 #include <signal.h>
@@ -378,6 +378,89 @@ ssl_get_certificate(InputStream stream)
     BIO_free_all(bp);
     return s;
 }
+
+Str
+ssl_check_cert_ident(SSL *handle, char *hostname)
+{
+    X509 *x;
+    int i;
+    Str ret = Strnew_charp("SSL error: failed to check certificate chain");
+    /*
+     * All we need to do here is check that the CN matches.
+     *
+     * From RFC2818 3.1 Server Identity:
+     * If a subjectAltName extension of type dNSName is present, that MUST
+     * be used as the identity. Otherwise, the (most specific) Common Name
+     * field in the Subject field of the certificate MUST be used. Although
+     * the use of the Common Name is existing practice, it is deprecated and
+     * Certification Authorities are encouraged to use the dNSName instead.
+     */
+    x = SSL_get_peer_certificate(handle);
+    if (!x) {   
+	ret = Strnew_charp("Unable to get peer certificate");
+	return ret;
+    }
+
+    i = X509_get_ext_by_NID(x, NID_subject_alt_name, -1);
+    if (i >= 0) {   
+        X509_EXTENSION *ex;
+        STACK_OF(GENERAL_NAME) *alt;
+
+        ex = X509_get_ext(x, i);
+        alt = X509V3_EXT_d2i(ex);
+        if (alt) {   
+            int n, len1, len2 = 0;
+            char *domain;
+            GENERAL_NAME *gn;
+            X509V3_EXT_METHOD *method;
+
+            len1 = strlen(hostname);
+            n = sk_GENERAL_NAME_num(alt);
+            domain = strchr(hostname, '.');
+            if (domain)
+                len2 = len1 - (domain - hostname);
+            for (i = 0; i < n; i++) {
+                gn = sk_GENERAL_NAME_value(alt, i);
+                if (gn->type == GEN_DNS) {
+                    char *sn = ASN1_STRING_data(gn->d.ia5);
+                    int sl = ASN1_STRING_length(gn->d.ia5);
+
+                    /* Is this an exact match? */
+                    if ((len1 == sl) && !strncasecmp(hostname, sn, len1))
+                        break;
+
+                    /* Is this a wildcard match? */
+                    if ((*sn == '*') && domain && (len2 == sl-1) &&
+                        !strncasecmp(domain, sn+1, len2))
+                        break;
+                }
+            }
+            method = X509V3_EXT_get(ex);
+            method->ext_free(alt);
+            if (i < n)  /* Found a match */
+                ret = NULL;
+        }
+    }
+
+    if (ret != NULL) {
+        X509_NAME *xn;
+        char buf[2048];
+
+        xn = X509_get_subject_name(x);
+
+        if (X509_NAME_get_text_by_NID(xn, NID_commonName, 
+				      buf, sizeof(buf)) == -1) {
+	    ret = Strnew_charp("Unable to get common name from peer cert");
+	    return ret;
+        }
+	else if (strcasecmp(hostname, buf))
+	    ret = Sprintf("Bad cert ident %s from %s", buf, hostname);
+	else
+	    ret = NULL;
+    }
+    X509_free(x);
+    return ret;
+}
 #endif
 
 /* Raw level input stream functions */

istream.h

@@ -1,4 +1,4 @@
-/* $Id: istream.h,v 1.4 2001/11/24 02:01:26 ukai Exp $ */
+/* $Id: istream.h,v 1.5 2001/12/26 12:18:06 ukai Exp $ */
 #ifndef IO_STREAM_H
 #define IO_STREAM_H
 
@@ -6,6 +6,7 @@
 #ifdef USE_SSL
 #include <bio.h>
 #include <x509.h>
+#include <x509v3.h>
 #include <ssl.h>
 #endif
 #include "Str.h"
@@ -126,6 +127,7 @@ extern int ISfileno(InputStream stream);
 extern int ISeos(InputStream stream);
 #ifdef USE_SSL
 extern Str ssl_get_certificate(InputStream stream);
+extern Str ssl_check_cert_ident(SSL *handle, char *hostname);
 #endif
 
 #define IST_BASIC	0

url.c

@@ -1,4 +1,4 @@
-/* $Id: url.c,v 1.22 2001/12/07 07:58:07 ukai Exp $ */
+/* $Id: url.c,v 1.23 2001/12/26 12:18:06 ukai Exp $ */
 #include "fm.h"
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -239,6 +239,7 @@ free_ssl_ctx()
 {
     if (ssl_ctx != NULL)
 	SSL_CTX_free(ssl_ctx);
+    ssl_ctx = NULL;
 }
 
 #if SSLEAY_VERSION_NUMBER >= 0x00905100
@@ -272,10 +273,12 @@ init_PRNG()
 #endif				/* SSLEAY_VERSION_NUMBER >= 0x00905100 */
 
 static SSL *
-openSSLHandle(int sock)
+openSSLHandle(int sock, char *hostname)
 {
     SSL *handle;
-    char *emsg;
+    Str emsg;
+    Str amsg = NULL;
+    char *ans;
     static char *old_ssl_forbid_method = NULL;
 #ifdef USE_SSL_VERIFY
     static int old_ssl_verify_server = -1;
@@ -288,7 +291,6 @@ openSSLHandle(int sock)
 	ssl_path_modified = 1;
 #else
 	free_ssl_ctx();
-	ssl_ctx = NULL;
 #endif
     }
 #ifdef USE_SSL_VERIFY
@@ -298,7 +300,6 @@ openSSLHandle(int sock)
     }
     if (ssl_path_modified) {
 	free_ssl_ctx();
-	ssl_ctx = NULL;
 	ssl_path_modified = 0;
     }
 #endif				/* defined(USE_SSL_VERIFY) */
@@ -350,9 +351,6 @@ openSSLHandle(int sock)
 #endif				/* defined(USE_SSL_VERIFY) */
 	    SSL_CTX_set_default_verify_paths(ssl_ctx);
 #endif				/* SSLEAY_VERSION_NUMBER >= 0x0800 */
-/*** by inu
-        atexit(free_ssl_ctx);
-*/
     }
     handle = SSL_new(ssl_ctx);
     SSL_set_fd(handle, sock);
@@ -361,11 +359,53 @@ openSSLHandle(int sock)
 #endif				/* SSLEAY_VERSION_NUMBER >= 0x00905100 */
     if (SSL_connect(handle) <= 0)
 	goto eend;
+#ifdef USE_SSL_VERIFY
+    /* check the cert chain.
+     * The chain length is automatically checked by OpenSSL when we
+     * set the verify depth in the ctx.
+     */
+    if (ssl_verify_server && (SSL_get_verify_result(handle) != X509_V_OK)) {
+	emsg = Strnew_charp("Accept SSL session "
+			    "which certificate doesn't verify (y/n)?");
+	term_raw();
+	ans = inputChar(emsg->ptr);
+	if (tolower(*ans) == 'y') {
+	    amsg = Strnew_charp("Accept unsecure SSL session: "
+				"unverified certificate");
+	} else {
+	    char *e = "This SSL session was rejected "
+		"to prevent security violation";
+	    disp_err_message(e, FALSE);
+	    free_ssl_ctx();
+	    return NULL;
+	}
+    }
+#endif
+    
+    emsg = ssl_check_cert_ident(handle, hostname);
+    if (emsg != NULL) {
+	if (emsg->length > COLS - 16)
+	    Strshrink(emsg, emsg->length - (COLS - 16));
+	term_raw();
+	Strcat_charp(emsg, ": accept(y/n)?");
+	ans = inputChar(emsg->ptr);
+	if (tolower(*ans) == 'y') {
+	    amsg = Strnew_charp("Accept unsecure SSL session:"
+		"certificate ident mismatch");
+	} else {
+	    char *e = "This SSL session was rejected "
+		"to prevent security violation";
+	    disp_err_message(e, FALSE);
+	    free_ssl_ctx();
+	    return NULL;
+	}
+    }
+    if (amsg)
+	disp_err_message(amsg->ptr, FALSE);
     return handle;
   eend:
-    emsg =
+    emsg = Sprintf("SSL error: %s", ERR_error_string(ERR_get_error(), NULL));
-	Sprintf("SSL error: %s", ERR_error_string(ERR_get_error(), NULL))->ptr;
+    disp_err_message(emsg->ptr, FALSE);
-    disp_err_message(emsg, FALSE);
     return NULL;
 }
 
@@ -1522,7 +1562,7 @@ openURL(char *url, ParsedURL *pu, ParsedURL *current,
 #ifdef USE_SSL
 	    if (pu->scheme == SCM_HTTPS && *status == HTST_CONNECT) {
 		sock = ssl_socket_of(ouf->stream);
-		if (!(sslh = openSSLHandle(sock))) {
+		if (!(sslh = openSSLHandle(sock, pu->host))) {
 		    *status = HTST_MISSING;
 		    return uf;
 		}
@@ -1576,7 +1616,7 @@ openURL(char *url, ParsedURL *pu, ParsedURL *current,
 	    }
 #ifdef USE_SSL
 	    if (pu->scheme == SCM_HTTPS) {
-		if (!(sslh = openSSLHandle(sock))) {
+		if (!(sslh = openSSLHandle(sock, pu->host))) {
 		    *status = HTST_MISSING;
 		    return uf;
 		}