Don't restrict the number of KeyUpdate messages we can process

Prior to this commit we were keeping a count of how many KeyUpdates we
have processed and failing if we had had too many. This simplistic approach
is not sufficient for long running connections. Since many KeyUpdates
would not be a particular good DoS route anyway, the simplest solution is
to simply remove the key update count.

Fixes #8068

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/8299)

4 files changed, 53 insertions, 12 deletions

diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index bd0d4210f4..ae6417b592 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -1178,8 +1178,6 @@ struct ssl_st {
     EVP_CIPHER_CTX *enc_write_ctx; /* cryptographic state */
     unsigned char write_iv[EVP_MAX_IV_LENGTH]; /* TLSv1.3 static write IV */
     EVP_MD_CTX *write_hash;     /* used for mac generation */
-    /* Count of how many KeyUpdate messages we have received */
-    unsigned int key_update_count;
     /* session info */
     /* client cert? */
     /* This is used to hold the server certificate used */
diff --git a/ssl/statem/statem_lib.c b/ssl/statem/statem_lib.c
index 8a7ada8f51..a18c5cccf4 100644
--- a/ssl/statem/statem_lib.c
+++ b/ssl/statem/statem_lib.c
@@ -614,13 +614,6 @@ MSG_PROCESS_RETURN tls_process_key_update(SSL *s, PACKET *pkt)
 {
     unsigned int updatetype;
 
-    s->key_update_count++;
-    if (s->key_update_count > MAX_KEY_UPDATE_MESSAGES) {
-        SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER, SSL_F_TLS_PROCESS_KEY_UPDATE,
-                 SSL_R_TOO_MANY_KEY_UPDATES);
-        return MSG_PROCESS_ERROR;
-    }
-
     /*
      * A KeyUpdate message signals a key change so the end of the message must
      * be on a record boundary.
diff --git a/ssl/statem/statem_locl.h b/ssl/statem/statem_locl.h
index 9c8c753cca..8f27deb9c5 100644
--- a/ssl/statem/statem_locl.h
+++ b/ssl/statem/statem_locl.h
@@ -29,9 +29,6 @@
 /* Max should actually be 36 but we are generous */
 #define FINISHED_MAX_LENGTH             64
 
-/* The maximum number of incoming KeyUpdate messages we will accept */
-#define MAX_KEY_UPDATE_MESSAGES     32
-
 /* Dummy message type */
 #define SSL3_MT_DUMMY   -1
 
diff --git a/test/sslapitest.c b/test/sslapitest.c
index 788ac4609e..2a4596dce9 100644
--- a/test/sslapitest.c
+++ b/test/sslapitest.c
@@ -4480,6 +4480,58 @@ static int test_export_key_mat_early(int idx)
 
     return testresult;
 }
+
+#define NUM_KEY_UPDATE_MESSAGES 40
+/*
+ * Test KeyUpdate.
+ */
+static int test_key_update(void)
+{
+    SSL_CTX *cctx = NULL, *sctx = NULL;
+    SSL *clientssl = NULL, *serverssl = NULL;
+    int testresult = 0, i, j;
+    char buf[20];
+    static char *mess = "A test message";
+
+    if (!TEST_true(create_ssl_ctx_pair(TLS_server_method(),
+                                       TLS_client_method(),
+                                       TLS1_3_VERSION,
+                                       0,
+                                       &sctx, &cctx, cert, privkey))
+            || !TEST_true(create_ssl_objects(sctx, cctx, &serverssl, &clientssl,
+                                             NULL, NULL))
+            || !TEST_true(create_ssl_connection(serverssl, clientssl,
+                                                SSL_ERROR_NONE)))
+        goto end;
+
+    for (j = 0; j < 2; j++) {
+        /* Send lots of KeyUpdate messages */
+        for (i = 0; i < NUM_KEY_UPDATE_MESSAGES; i++) {
+            if (!TEST_true(SSL_key_update(clientssl,
+                                          (j == 0)
+                                          ? SSL_KEY_UPDATE_NOT_REQUESTED
+                                          : SSL_KEY_UPDATE_REQUESTED))
+                    || !TEST_true(SSL_do_handshake(clientssl)))
+                goto end;
+        }
+
+        /* Check that sending and receiving app data is ok */
+        if (!TEST_int_eq(SSL_write(clientssl, mess, strlen(mess)), strlen(mess))
+                || !TEST_int_eq(SSL_read(serverssl, buf, sizeof(buf)),
+                                         strlen(mess)))
+            goto end;
+    }
+
+    testresult = 1;
+
+ end:
+    SSL_free(serverssl);
+    SSL_free(clientssl);
+    SSL_CTX_free(sctx);
+    SSL_CTX_free(cctx);
+
+    return testresult;
+}
 #endif /* OPENSSL_NO_TLS1_3 */
 
 static int test_ssl_clear(int idx)
@@ -6170,6 +6222,7 @@ int setup_tests(void)
     ADD_ALL_TESTS(test_export_key_mat, 6);
 #ifndef OPENSSL_NO_TLS1_3
     ADD_ALL_TESTS(test_export_key_mat_early, 3);
+    ADD_TEST(test_key_update);
 #endif
     ADD_ALL_TESTS(test_ssl_clear, 2);
     ADD_ALL_TESTS(test_max_fragment_len_ext, OSSL_NELEM(max_fragment_len_test));