Add support to libtls for client-side TLS session resumption.

A libtls client can specify a session file descriptor (a regular file
with appropriate ownership and permissions) and libtls will manage reading
and writing of session data across TLS handshakes.

Discussed at length with deraadt@ and tedu@.

Rides previous minor bump.

ok beck@

1 files changed, 127 insertions, 1 deletions

diff --git a/src/lib/libtls/tls_client.c b/src/lib/libtls/tls_client.c
index c79f462a3a..14c716fa17 100644
--- a/src/lib/libtls/tls_client.c
+++ b/src/lib/libtls/tls_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls_client.c,v 1.43 2017/08/10 18:18:30 jsing Exp $ */
+/* $OpenBSD: tls_client.c,v 1.44 2018/02/10 04:41:24 jsing Exp $ */
 /*
  * Copyright (c) 2014 Joel Sing <jsing@openbsd.org>
  *
@@ -17,10 +17,12 @@
 
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 
 #include <arpa/inet.h>
 #include <netinet/in.h>
 
+#include <limits.h>
 #include <netdb.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -159,6 +161,118 @@ tls_connect_servername(struct tls *ctx, const char *host, const char *port,
 }
 
 static int
+tls_client_read_session(struct tls *ctx)
+{
+        int sfd = ctx->config->session_fd;
+        uint8_t *session = NULL;
+        size_t session_len = 0;
+        SSL_SESSION *ss = NULL;
+        BIO *bio = NULL;
+        struct stat sb;
+        ssize_t n;
+        int rv = -1;
+
+        if (fstat(sfd, &sb) == -1) {
+                tls_set_error(ctx, "failed to stat session file");
+                goto err;
+        }
+        if (sb.st_size < 0 || sb.st_size > INT_MAX) {
+                tls_set_errorx(ctx, "invalid session file size");
+                goto err;
+        }
+        session_len = (size_t)sb.st_size;
+
+        /* A zero size file means that we do not yet have a valid session. */
+        if (session_len == 0)
+                goto done;
+
+        if ((session = malloc(session_len)) == NULL)
+                goto err;
+
+        n = pread(sfd, session, session_len, 0);
+        if (n < 0 || (size_t)n != session_len) {
+                tls_set_error(ctx, "failed to read session file");
+                goto err;
+        }
+        if ((bio = BIO_new_mem_buf(session, session_len)) == NULL)
+                goto err;
+        if ((ss = PEM_read_bio_SSL_SESSION(bio, NULL, tls_password_cb,
+            NULL)) == NULL) {
+                tls_set_errorx(ctx, "failed to parse session");
+                goto err;
+        }
+
+        if (SSL_set_session(ctx->ssl_conn, ss) != 1) {
+                tls_set_errorx(ctx, "failed to set session");
+                goto err;
+        }
+
+ done:
+        rv = 0;
+
+ err:
+        freezero(session, session_len);
+        SSL_SESSION_free(ss);
+        BIO_free(bio);
+
+        return rv;
+}
+
+static int
+tls_client_write_session(struct tls *ctx)
+{
+        int sfd = ctx->config->session_fd;
+        SSL_SESSION *ss = NULL;
+        BIO *bio = NULL;
+        long data_len;
+        char *data;
+        off_t offset;
+        size_t len;
+        ssize_t n;
+        int rv = -1;
+
+        if ((ss = SSL_get1_session(ctx->ssl_conn)) == NULL) {
+                if (ftruncate(sfd, 0) == -1) {
+                        tls_set_error(ctx, "failed to truncate session file");
+                        goto err;
+                }
+                goto done;
+        }
+
+        if ((bio = BIO_new(BIO_s_mem())) == NULL)
+                goto err;
+        if (PEM_write_bio_SSL_SESSION(bio, ss) == 0)
+                goto err;
+        if ((data_len = BIO_get_mem_data(bio, &data)) <= 0)
+                goto err;
+
+        len = (size_t)data_len;
+        offset = 0;
+
+        if (ftruncate(sfd, len) == -1) {
+                tls_set_error(ctx, "failed to truncate session file");
+                goto err;
+        }
+        while (len > 0) {
+                if ((n = pwrite(sfd, data + offset, len, offset)) == -1) {
+                        tls_set_error(ctx, "failed to write session file");
+                        goto err;
+                }
+                offset += n;
+                len -= n;
+        }
+
+ done:
+        rv = 0;
+
+ err:
+        SSL_SESSION_free(ss);
+        BIO_free_all(bio);
+
+        return (rv);
+}
+
+static int
 tls_connect_common(struct tls *ctx, const char *servername)
 {
         union tls_addr addrbuf;
@@ -221,6 +335,12 @@ tls_connect_common(struct tls *ctx, const char *servername)
                 goto err;
         }
 
+        if (ctx->config->session_fd != -1) {
+                SSL_clear_options(ctx->ssl_conn, SSL_OP_NO_TICKET);
+                if (tls_client_read_session(ctx) == -1)
+                        goto err;
+        }
+
         if (SSL_set_tlsext_status_type(ctx->ssl_conn, TLSEXT_STATUSTYPE_ocsp) != 1) {
                 tls_set_errorx(ctx, "ssl OCSP extension setup failure");
                 goto err;
@@ -336,6 +456,12 @@ tls_handshake_client(struct tls *ctx)
         }
 
         ctx->state |= TLS_HANDSHAKE_COMPLETE;
+
+        if (ctx->config->session_fd != -1) {
+                if (tls_client_write_session(ctx) == -1)
+                        goto err;
+        }
+
         rv = 0;
 
  err: