If a non-NBD client connects to qemu-nbd, we would end up with a SIGSEGV in nbd_cilent_put() because we were trying to unregister the client's association to the export, even though we skipped inserting the client into that list. Easy trigger in two terminals:
$ qemu-nbd -p 30001 --format=raw file $ nmap 127.0.0.1 -p 30001 nmap claims that it thinks it connected to a pago-services1 server (which probably means nmap could be updated to learn the NBD protocol and give a more accurate diagnosis of the open port - but that's not our problem), then terminates immediately, so our call to nbd_negotiate() fails. The fix is to reorder nbd_co_client_start() to ensure that all initialization occurs before we ever try talking to a client in nbd_negotiate(), so that the teardown sequence on negotiation failure doesn't fault while dereferencing a half-initialized object. While debugging this, I also noticed that nbd_update_server_watch() called by nbd_client_closed() was still adding a channel to accept the next client, even when the state was no longer RUNNING. That is fixed by making nbd_can_accept() pay attention to the current state. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451614 Signed-off-by: Eric Blake <ebl...@redhat.com> --- I'm planning to run a bisect to see which patch actually introduced the problem, but wanted to post the patch first to get review started. nbd/server.c | 14 ++++++-------- qemu-nbd.c | 2 +- 2 files changed, 7 insertions(+), 9 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index 0c4f456..d8dfac8 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1601,16 +1601,14 @@ static coroutine_fn void nbd_co_client_start(void *opaque) if (exp) { nbd_export_get(exp); - } - if (nbd_negotiate(data)) { - client_close(client); - goto out; - } - qemu_co_mutex_init(&client->send_lock); - - if (exp) { QTAILQ_INSERT_TAIL(&exp->clients, client, next); } + qemu_co_mutex_init(&client->send_lock); + + if (nbd_negotiate(data)) { + client_close(client); + goto out; + } nbd_client_receive_next_request(client); diff --git a/qemu-nbd.c b/qemu-nbd.c index 27a4e3a..5410854 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -322,7 +322,7 @@ out: static int nbd_can_accept(void) { - return nb_fds < shared; + return state == RUNNING && nb_fds < shared; } static void nbd_export_closed(NBDExport *exp) -- 2.9.4