Suppress DANE TLSA reflection when verification fails

As documented both SSL_get0_dane_authority() and SSL_get0_dane_tlsa()
are expected to return a negative match depth and nothing else when
verification fails.  However, this only happened when verification
failed during chain construction.  Errors in verification of the
constructed chain did not have the intended effect on these functions.

This commit updates the functions to check for verify_result ==
X509_V_OK, and no longer erases any accumulated match information
when chain construction fails.  Sophisticated developers can, with
care, use SSL_set_verify_result(ssl, X509_V_OK) to "peek" at TLSA
info even when verification fail.  They must of course first check
and save the real error, and restore the original error as quickly
as possible.  Hiding by default seems to be the safer interface.

Introduced X509_V_ERR_DANE_NO_MATCH code to signal failure to find
matching TLSA records.  Previously reported via X509_V_ERR_CERT_UNTRUSTED.

This also changes the "-brief" output from s_client to include
verification results and TLSA match information.

Mentioned session resumption in code example in SSL_CTX_dane_enable(3).
Also mentioned that depths returned are relative to the verified chain
which is now available via SSL_get0_verified_chain(3).

Added a few more test-cases to danetest, that exercise the new
code.

Resolved thread safety issue in use of static buffer in
X509_verify_cert_error_string().

Fixed long-stating issue in apps/s_cb.c which always sets verify_error
to either X509_V_OK or "chain to long", code elsewhere (e.g.
s_time.c), seems to expect the actual error.  [ The new chain
construction code is expected to correctly generate "chain
too long" errors, so at some point we need to drop the
work-arounds, once SSL_set_verify_depth() is also fixed to
propagate the depth to X509_STORE_CTX reliably. ]

Reviewed-by: Rich Salz <rsalz@openssl.org>

3 files changed, 79 insertions, 16 deletions

diff --git a/apps/s_apps.h b/apps/s_apps.h
index e9b6f40288..8e12c2146c 100644
--- a/apps/s_apps.h
+++ b/apps/s_apps.h
@@ -192,6 +192,7 @@ void ssl_ctx_set_excert(SSL_CTX *ctx, SSL_EXCERT *exc);
 void ssl_excert_free(SSL_EXCERT *exc);
 int args_excert(int option, SSL_EXCERT **pexc);
 int load_excert(SSL_EXCERT **pexc);
+void print_verify_detail(SSL *s, BIO *bio);
 void print_ssl_summary(SSL *s);
 #ifdef HEADER_SSL_H
 int config_ctx(SSL_CONF_CTX *cctx, STACK_OF(OPENSSL_STRING) *str,
diff --git a/apps/s_cb.c b/apps/s_cb.c
index 096471a86f..30c9147d5c 100644
--- a/apps/s_cb.c
+++ b/apps/s_cb.c
@@ -167,7 +167,7 @@ int verify_callback(int ok, X509_STORE_CTX *ctx)
         if (verify_depth >= depth) {
             if (!verify_return_error)
                 ok = 1;
-            verify_error = X509_V_OK;
+            verify_error = err;
         } else {
             ok = 0;
             verify_error = X509_V_ERR_CERT_CHAIN_TOO_LONG;
@@ -1086,6 +1086,80 @@ static void print_raw_cipherlist(SSL *s)
     BIO_puts(bio_err, "\n");
 }
 
+/*
+ * Hex encoder for TLSA RRdata, not ':' delimited.
+ */
+static char *hexencode(const unsigned char *data, size_t len)
+{
+    static const char *hex = "0123456789abcdef";
+    char *out;
+    char *cp;
+    size_t outlen = 2 * len + 1;
+    int ilen = (int) outlen;
+
+    if (outlen < len || ilen < 0 || outlen != (size_t)ilen) {
+        BIO_printf(bio_err, "%s: %" PRIu64 "-byte buffer too large to hexencode\n",
+                   opt_getprog(), (uint64_t)len);
+        exit(1);
+    }
+    cp = out = app_malloc(ilen, "TLSA hex data buffer");
+
+    while (ilen-- > 0) {
+        *cp++ = hex[(*data >> 4) & 0x0f];
+        *cp++ = hex[*data++ & 0x0f];
+    }
+    *cp = '\0';
+    return out;
+}
+
+void print_verify_detail(SSL *s, BIO *bio)
+{
+    int mdpth;
+    EVP_PKEY *mspki;
+    long verify_err = SSL_get_verify_result(s);
+
+    if (verify_err == X509_V_OK) {
+        const char *peername = SSL_get0_peername(s);
+
+        BIO_printf(bio, "Verification: OK\n");
+        if (peername != NULL)
+            BIO_printf(bio, "Verified peername: %s\n", peername);
+    } else {
+        const char *reason = X509_verify_cert_error_string(verify_err);
+
+        BIO_printf(bio, "Verification error: %s\n", reason);
+    }
+
+    if ((mdpth = SSL_get0_dane_authority(s, NULL, &mspki)) >= 0) {
+        uint8_t usage, selector, mtype;
+        const unsigned char *data = NULL;
+        size_t dlen = 0;
+        char *hexdata;
+
+        mdpth = SSL_get0_dane_tlsa(s, &usage, &selector, &mtype, &data, &dlen);
+
+        /*
+         * The TLSA data field can be quite long when it is a certificate,
+         * public key or even a SHA2-512 digest.  Because the initial octets of
+         * ASN.1 certificates and public keys contain mostly boilerplate OIDs
+         * and lengths, we show the last 12 bytes of the data instead, as these
+         * are more likely to distinguish distinct TLSA records.
+         */
+#define TLSA_TAIL_SIZE 12
+        if (dlen > TLSA_TAIL_SIZE)
+            hexdata = hexencode(data + dlen - TLSA_TAIL_SIZE, TLSA_TAIL_SIZE);
+        else
+            hexdata = hexencode(data, dlen);
+        BIO_printf(bio, "DANE TLSA %d %d %d %s%s %s at depth %d\n",
+                   usage, selector, mtype,
+                   (dlen > TLSA_TAIL_SIZE) ? "..." : "", hexdata,
+                   (mspki != NULL) ? "signed the certificate" :
+                   mdpth ? "matched TA certificate" : "matched EE certificate",
+                   mdpth);
+        OPENSSL_free(hexdata);
+    }
+}
+
 void print_ssl_summary(SSL *s)
 {
     const SSL_CIPHER *c;
@@ -1100,12 +1174,14 @@ void print_ssl_summary(SSL *s)
     peer = SSL_get_peer_certificate(s);
     if (peer) {
         int nid;
+
         BIO_puts(bio_err, "Peer certificate: ");
         X509_NAME_print_ex(bio_err, X509_get_subject_name(peer),
                            0, XN_FLAG_ONELINE);
         BIO_puts(bio_err, "\n");
         if (SSL_get_peer_signature_nid(s, &nid))
             BIO_printf(bio_err, "Hash used: %s\n", OBJ_nid2sn(nid));
+        print_verify_detail(s, bio_err);
     } else
         BIO_puts(bio_err, "No peer certificate\n");
     X509_free(peer);
diff --git a/apps/s_client.c b/apps/s_client.c
index 39e3e48288..8fe16121a9 100644
--- a/apps/s_client.c
+++ b/apps/s_client.c
@@ -2461,9 +2461,6 @@ static void print_stuff(BIO *bio, SSL *s, int full)
     const SSL_CIPHER *c;
     X509_NAME *xn;
     int i;
-    int mdpth;
-    EVP_PKEY *mspki;
-    const char *peername;
 #ifndef OPENSSL_NO_COMP
     const COMP_METHOD *comp, *expansion;
 #endif
@@ -2525,18 +2522,7 @@ static void print_stuff(BIO *bio, SSL *s, int full)
                    BIO_number_read(SSL_get_rbio(s)),
                    BIO_number_written(SSL_get_wbio(s)));
     }
-    if ((mdpth = SSL_get0_dane_authority(s, NULL, &mspki)) >= 0) {
-        uint8_t usage, selector, mtype;
-        mdpth = SSL_get0_dane_tlsa(s, &usage, &selector, &mtype, NULL, NULL);
-        BIO_printf(bio, "DANE TLSA %d %d %d %s at depth %d\n",
-                   usage, selector, mtype,
-                   (mspki != NULL) ? "TA public key verified certificate" :
-                   mdpth ? "matched TA certificate" : "matched EE certificate",
-                   mdpth);
-    }
-    if (SSL_get_verify_result(s) == X509_V_OK &&
-        (peername = SSL_get0_peername(s)) != NULL)
-        BIO_printf(bio, "Verified peername: %s\n", peername);
+    print_verify_detail(s, bio);
     BIO_printf(bio, (SSL_session_reused(s) ? "---\nReused, " : "---\nNew, "));
     c = SSL_get_current_cipher(s);
     BIO_printf(bio, "%s, Cipher is %s\n",