Improve X.509 certificate validation reporting.

* Improved reporting when SSL/TLS X.509 certificate validation has failed,
  working around a not-so-recent swapping of two OpenSSL error codes, and
  a practical impossibility to distinguish broken certification chains from
  missing trust anchors (root certificates).
* OpenSSL decoded errors are now reported through report(), rather than dumped
  to stderr, so that they should show up in logfiles and/or syslog.

1 files changed, 42 insertions, 13 deletions

diff --git a/socket.c b/socket.c
index 3e4a3acd..48201d38 100644
--- a/socket.c
+++ b/socket.c
@@ -375,6 +375,20 @@ va_dcl {
 #include <openssl/x509v3.h>
 #include <openssl/rand.h>
 
+static void report_SSL_errors(FILE *stream)
+{
+    unsigned long err;
+
+    while (0ul != (err = ERR_get_error())) {
+	char *errstr = ERR_error_string(err, NULL);
+	report(stream, GT_("OpenSSL reported: %s\n"), errstr);
+    }
+}
+
+/* override ERR_print_errors_fp to our own implementation */
+#undef ERR_print_errors_fp
+#define ERR_print_errors_fp(stream) report_SSL_errors((stream))
+
 static	SSL_CTX *_ctx[FD_SETSIZE];
 static	SSL *_ssl_context[FD_SETSIZE];
 
@@ -755,29 +769,44 @@ static int SSL_verify_callback( int ok_return, X509_STORE_CTX *ctx, int strict )
 	} /* if (depth == 0 && !_depth0ck) */
 
 	if (err != X509_V_OK && err != _prev_err && !(_check_fp != 0 && _check_digest && !strict)) {
+		char *tmp;
+		int did_rep_err = 0;
 		_prev_err = err;
-					
+
                 report(stderr, GT_("Server certificate verification error: %s\n"), X509_verify_cert_error_string(err));
                 /* We gave the error code, but maybe we can add some more details for debugging */
 
 		switch (err) {
+		/* actually we do not want to lump these together, but
+		 * since OpenSSL flipped the meaning of these error
+		 * codes in the past, and they do hardly make a
+		 * practical difference because servers need not provide
+		 * the root signing certificate, we don't bother telling
+		 * users the difference:
+		 */
+		case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY:
 		case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
 			X509_NAME_oneline(issuer, buf, sizeof(buf));
 			buf[sizeof(buf) - 1] = '\0';
-			report(stderr, GT_("unknown issuer (first %d characters): %s\n"), (int)(sizeof(buf)-1), buf);
-			report(stderr, GT_("This error usually happens when the server provides an incomplete certificate "
-						"chain, which is nothing fetchmail could do anything about.  For details, "
-						"please see the README.SSL-SERVER document that comes with fetchmail.\n"));
-			break;
+			report(stderr, GT_("Broken certification chain at: %s\n"), (tmp = sdump(buf, strlen(buf))));
+			xfree(tmp);
+			report(stderr, GT_(	"This could mean that the server did not provide the intermediate CA's certificate(s), "
+						"which is nothing fetchmail could do anything about.  For details, "
+						"please see the README.SSL-SERVER document that ships with fetchmail.\n"));
+			did_rep_err = 1;
+			/* FALLTHROUGH */
 		case X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT:
-		case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY:
 		case X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN:
-			X509_NAME_oneline(subj, buf, sizeof(buf));
-			buf[sizeof(buf) - 1] = '\0';
-			report(stderr, GT_("This means that the root signing certificate (issued for %s) is not in the "
-						"trusted CA certificate locations, or that c_rehash needs to be run "
+			if (!did_rep_err) {
+			    X509_NAME_oneline(issuer, buf, sizeof(buf));
+			    buf[sizeof(buf) - 1] = '\0';
+			    report(stderr, GT_("Missing trust anchor certificate: %s\n"), (tmp = sdump(buf, strlen(buf))));
+			    xfree(tmp);
+			}
+			report(stderr, GT_(	"This could mean that the root CA's signing certificate is not in the "
+						"trusted CA certificate location, or that c_rehash needs to be run "
 						"on the certificate directory. For details, please "
-						"see the documentation of --sslcertpath and --sslcertfile in the manual page.\n"), buf);
+						"see the documentation of --sslcertpath and --sslcertfile in the manual page.\n"));
 			break;
 		default:
 			break;
@@ -888,7 +917,7 @@ int SSLOpen(int sock, char *mycert, char *mykey, const char *myproto, int certck
 		} else if (!strcasecmp("ssl23",myproto)) {
 			myproto = NULL;
 		} else {
-			fprintf(stderr,GT_("Invalid SSL protocol '%s' specified, using default (SSLv23).\n"), myproto);
+			report(stderr,GT_("Invalid SSL protocol '%s' specified, using default (SSLv23).\n"), myproto);
 			myproto = NULL;
 		}
 	}