From d1129a8ad96af6bc47404490769a637bcd860493 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 14 Apr 2016 16:02:23 -0600 Subject: nbd: Don't kill server on client that doesn't request TLS Upstream NBD documents (as of commit 4feebc95) that servers MAY choose to operate in a conditional mode, where it is up to the client whether to use TLS. For qemu's case, we want to always be in FORCEDTLS mode, because of the risk of man-in-the-middle attacks, and since we never export more than one device; likewise, the qemu client will ALWAYS send NBD_OPT_STARTTLS as its first option. But now that SELECTIVETLS servers exist, it is feasible to encounter a (non-qemu) client that is programmed to talk to such a server, and does not do NBD_OPT_STARTTLS first, but rather wants to probe if it can use a non-encrypted export. The NBD protocol documents that we should let such a client continue trying, on the grounds that maybe the client will get the hint to send NBD_OPT_STARTTLS, rather than immediately dropping the connection. Note that NBD_OPT_EXPORT_NAME is a special case: since it is the only option request that can't have an error return, we have to (continue to) drop the connection on that one; rather, what we are fixing here is that all other replies prior to TLS initiation tell the client NBD_REP_ERR_TLS_REQD, but keep the connection alive. Signed-off-by: Eric Blake Message-id: 1460671343-18485-1-git-send-email-eblake@redhat.com Signed-off-by: Max Reitz --- nbd/server.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index 2a4dd10f52..a13a69169a 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -449,11 +449,19 @@ static int nbd_negotiate_options(NBDClient *client) client->ioc = QIO_CHANNEL(tioc); break; + case NBD_OPT_EXPORT_NAME: + /* No way to return an error to client, so drop connection */ + TRACE("Option 0x%x not permitted before TLS", clientflags); + return -EINVAL; + default: TRACE("Option 0x%x not permitted before TLS", clientflags); + if (nbd_negotiate_drop_sync(client->ioc, length) != length) { + return -EIO; + } nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_TLS_REQD, clientflags); - return -EINVAL; + break; } } else if (fixedNewstyle) { switch (clientflags) { @@ -471,6 +479,9 @@ static int nbd_negotiate_options(NBDClient *client) return nbd_negotiate_handle_export_name(client, length); case NBD_OPT_STARTTLS: + if (nbd_negotiate_drop_sync(client->ioc, length) != length) { + return -EIO; + } if (client->tlscreds) { TRACE("TLS already enabled"); nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_INVALID, @@ -480,7 +491,7 @@ static int nbd_negotiate_options(NBDClient *client) nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_POLICY, clientflags); } - return -EINVAL; + break; default: TRACE("Unsupported option 0x%x", clientflags); if (nbd_negotiate_drop_sync(client->ioc, length) != length) { -- cgit v1.2.1