Avoid failing s_server when client's psk_identity is unexpected

s_server has traditionally been very brittle in PSK mode.  If the
client offered any PSK identity other than "Client_identity" s_server
would simply abort.

This is breakage for breakage's sake, and unlike most other parts of
s_server, which tend to allow more flexible connections.

This change accomplishes two things:

 * when the client's psk_identity does *not* match the identity
   expected by the server, just warn, don't fail.

 * allow the server to expect instead a different psk_identity from
   the client besides "Client_identity"

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3605)

diff --git a/apps/s_server.c b/apps/s_server.c
index 815549b0c67965750cc3c2347944c3bef133d0e6..82fe5a4b7449b32e691c48063b4f60b8c4d7113c 100644 (file)
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -149,7 +149,7 @@ static int dtlslisten = 0;
 static int early_data = 0;
 
 #ifndef OPENSSL_NO_PSK
-static const char psk_identity[] = "Client_identity";
+static char *psk_identity = "Client_identity";
 char *psk_key = NULL;           /* by default PSK is not used */
 
 static unsigned int psk_server_cb(SSL *ssl, const char *identity,
@@ -171,12 +171,12 @@ static unsigned int psk_server_cb(SSL *ssl, const char *identity,
 
     /* here we could lookup the given identity e.g. from a database */
     if (strcmp(identity, psk_identity) != 0) {
-        BIO_printf(bio_s_out, "PSK error: client identity not found"
+        BIO_printf(bio_s_out, "PSK warning: client identity not what we expected"
                    " (got '%s' expected '%s')\n", identity, psk_identity);
-        goto out_err;
-    }
-    if (s_debug)
+    } else {
+      if (s_debug)
         BIO_printf(bio_s_out, "PSK client identity found\n");
+    }
 
     /* convert the PSK key to binary */
     key = OPENSSL_hexstr2buf(psk_key, &key_len);
@@ -715,7 +715,7 @@ typedef enum OPTION_choice {
     OPT_STATUS_TIMEOUT, OPT_STATUS_URL, OPT_STATUS_FILE, OPT_MSG, OPT_MSGFILE,
     OPT_TRACE, OPT_SECURITY_DEBUG, OPT_SECURITY_DEBUG_VERBOSE, OPT_STATE,
     OPT_CRLF, OPT_QUIET, OPT_BRIEF, OPT_NO_DHE,
-    OPT_NO_RESUME_EPHEMERAL, OPT_PSK_HINT, OPT_PSK, OPT_SRPVFILE,
+    OPT_NO_RESUME_EPHEMERAL, OPT_PSK_IDENTITY, OPT_PSK_HINT, OPT_PSK, OPT_SRPVFILE,
     OPT_SRPUSERSEED, OPT_REV, OPT_WWW, OPT_UPPER_WWW, OPT_HTTP, OPT_ASYNC,
     OPT_SSL_CONFIG, 
     OPT_MAX_SEND_FRAG, OPT_SPLIT_SEND_FRAG, OPT_MAX_PIPELINES, OPT_READ_BUF,
@@ -869,6 +869,7 @@ const OPTIONS s_server_options[] = {
     OPT_X_OPTIONS,
     {"nbio", OPT_NBIO, '-', "Use non-blocking IO"},
 #ifndef OPENSSL_NO_PSK
+    {"psk_identity", OPT_PSK_IDENTITY, 's', "PSK identity to expect"},
     {"psk_hint", OPT_PSK_HINT, 's', "PSK identity hint to use"},
     {"psk", OPT_PSK, 's', "PSK in hex (without 0x)"},
 #endif
@@ -1351,6 +1352,11 @@ int s_server_main(int argc, char *argv[])
         case OPT_NO_RESUME_EPHEMERAL:
             no_resume_ephemeral = 1;
             break;
+        case OPT_PSK_IDENTITY:
+#ifndef OPENSSL_NO_PSK
+            psk_identity = opt_arg();
+#endif
+            break;
         case OPT_PSK_HINT:
 #ifndef OPENSSL_NO_PSK
             psk_identity_hint = opt_arg();

diff --git a/doc/man1/s_server.pod b/doc/man1/s_server.pod
index c3e763f4e0cb7d47416ea58def941f432957431e..b5245d8b4d8fe8cf8cb46b3a8adec787edf6dfda 100644 (file)
--- a/doc/man1/s_server.pod
+++ b/doc/man1/s_server.pod
@@ -333,6 +333,12 @@ Inhibit printing of session and certificate information.
 
 Use the PSK identity hint B<hint> when using a PSK cipher suite.
 
+=item B<-psk_identity identity>
+
+Expect the client to send PSK identity B<identity> when using a PSK
+cipher suite, and warn if they do not.  By default, the expected PSK
+identity is the string "Client_identity".
+
 =item B<-psk key>
 
 Use the PSK key B<key> when using a PSK cipher suite. The key is