nss: implement public key pinning for NSS backend

Bug: https://bugzilla.redhat.com/1195771

docs/curl.1

@@ -548,7 +548,8 @@ indicating its identity. A public key is extracted from this certificate and
 if it does not exactly match the public key provided to this option, curl will
 abort the connection before sending or receiving any data.
 
-This is currently only implemented in the OpenSSL, GnuTLS and GSKit backends.
+This is currently only implemented in the OpenSSL, GnuTLS, NSS and GSKit
+backends.
 
 If this option is used several times, the last one will be used.
 (Added in 7.39.0)

docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.3

@@ -52,7 +52,7 @@ if(curl) {
 .fi
 .SH AVAILABILITY
 If built TLS enabled. This is currently only implemented in the OpenSSL,
-GnuTLS and GSKit backends.
+GnuTLS, NSS and GSKit backends.
 
 Added in libcurl 7.39.0
 .SH RETURN VALUE

lib/vtls/nss.c

@@ -56,6 +56,7 @@
 #include <base64.h>
 #include <cert.h>
 #include <prerror.h>
+#include <keyhi.h>        /* for SECKEY_DestroyPublicKey() */
 
 #define NSSVERNUM ((NSS_VMAJOR<<16)|(NSS_VMINOR<<8)|NSS_VPATCH)
 
@@ -943,6 +944,53 @@ static SECStatus check_issuer_cert(PRFileDesc *sock,
   return res;
 }
 
+static CURLcode cmp_peer_pubkey(struct ssl_connect_data *connssl,
+                                const char *pinnedpubkey)
+{
+  CURLcode result = CURLE_SSL_PINNEDPUBKEYNOTMATCH;
+  struct SessionHandle *data = connssl->data;
+  CERTCertificate *cert;
+
+  if(!pinnedpubkey)
+    /* no pinned public key specified */
+    return CURLE_OK;
+
+  /* get peer certificate */
+  cert = SSL_PeerCertificate(connssl->handle);
+  if(cert) {
+    /* extract public key from peer certificate */
+    SECKEYPublicKey *pubkey = CERT_ExtractPublicKey(cert);
+    if(pubkey) {
+      /* encode the public key as DER */
+      SECItem *cert_der = PK11_DEREncodePublicKey(pubkey);
+      if(cert_der) {
+        /* compare the public key with the pinned public key */
+        result = Curl_pin_peer_pubkey(pinnedpubkey,
+                                      cert_der->data,
+                                      cert_der->len);
+        SECITEM_FreeItem(cert_der, PR_TRUE);
+      }
+      SECKEY_DestroyPublicKey(pubkey);
+    }
+    CERT_DestroyCertificate(cert);
+  }
+
+  /* report the resulting status */
+  switch(result) {
+  case CURLE_OK:
+    infof(data, "pinned public key verified successfully!\n");
+    break;
+  case CURLE_SSL_PINNEDPUBKEYNOTMATCH:
+    failf(data, "failed to verify pinned public key");
+    break;
+  default:
+    /* OOM, etc. */
+    break;
+  }
+
+  return result;
+}
+
 /**
  *
  * Callback to pick the SSL client certificate.
@@ -1806,6 +1854,11 @@ static CURLcode nss_do_connect(struct connectdata *conn, int sockindex)
     }
   }
 
+  result = cmp_peer_pubkey(connssl, data->set.str[STRING_SSL_PINNEDPUBLICKEY]);
+  if(result)
+    /* status already printed */
+    goto error;
+
   return CURLE_OK;
 
 error:

src/tool_help.c

@@ -156,7 +156,7 @@ static const char *const helptext[] = {
   "     --pass PASS     Pass phrase for the private key (SSL/SSH)",
   "     --path-as-is    Do not squash .. sequences in URL path",
   "     --pinnedpubkey FILE  Public key (PEM/DER) to verify peer against "
-  "(OpenSSL/GnuTLS/GSKit only)",
+  "(OpenSSL/GnuTLS/NSS/GSKit only)",
   "     --post301       "
   "Do not switch to GET after following a 301 redirect (H)",
   "     --post302       "

tests/runtests.pl

@@ -2346,6 +2346,7 @@ sub checksystem {
            }
            elsif ($libcurl =~ /nss/i) {
                $has_nss=1;
+               $has_sslpinning=1;
                $ssllib="NSS";
            }
            elsif ($libcurl =~ /(yassl|wolfssl)/i) {