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From df8ad9f128c15aa0a0ebc7b24e9a22c9775b67af Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Fri, 26 May 2017 22:04:21 -0500
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Subject: [PATCH] nbd: Fully initialize client in case of failed negotiation
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If a non-NBD client connects to qemu-nbd, we would end up with
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a SIGSEGV in nbd_client_put() because we were trying to
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unregister the client's association to the export, even though
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we skipped inserting the client into that list. Easy trigger
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in two terminals:
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$ qemu-nbd -p 30001 --format=raw file
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$ nmap 127.0.0.1 -p 30001
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nmap claims that it thinks it connected to a pago-services1
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server (which probably means nmap could be updated to learn the
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NBD protocol and give a more accurate diagnosis of the open
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port - but that's not our problem), then terminates immediately,
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so our call to nbd_negotiate() fails. The fix is to reorder
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nbd_co_client_start() to ensure that all initialization occurs
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before we ever try talking to a client in nbd_negotiate(), so
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that the teardown sequence on negotiation failure doesn't fault
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while dereferencing a half-initialized object.
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While debugging this, I also noticed that nbd_update_server_watch()
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called by nbd_client_closed() was still adding a channel to accept
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the next client, even when the state was no longer RUNNING. That
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is fixed by making nbd_can_accept() pay attention to the current
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state.
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451614
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Signed-off-by: Eric Blake <eblake@redhat.com>
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Message-Id: <20170527030421.28366-1-eblake@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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nbd/server.c | 8 +++-----
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qemu-nbd.c | 2 +-
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2 files changed, 4 insertions(+), 6 deletions(-)
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diff --git a/nbd/server.c b/nbd/server.c
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index ee59e5d..49b55f6 100644
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--- a/nbd/server.c
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+++ b/nbd/server.c
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@@ -1358,17 +1358,15 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
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if (exp) {
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nbd_export_get(exp);
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+ QTAILQ_INSERT_TAIL(&exp->clients, client, next);
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}
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+ qemu_co_mutex_init(&client->send_lock);
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+
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if (nbd_negotiate(data)) {
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client_close(client);
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goto out;
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}
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- qemu_co_mutex_init(&client->send_lock);
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nbd_set_handlers(client);
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-
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- if (exp) {
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- QTAILQ_INSERT_TAIL(&exp->clients, client, next);
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- }
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out:
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g_free(data);
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}
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diff --git a/qemu-nbd.c b/qemu-nbd.c
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index f60842f..651f85e 100644
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--- a/qemu-nbd.c
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+++ b/qemu-nbd.c
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@@ -325,7 +325,7 @@ out:
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static int nbd_can_accept(void)
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{
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- return nb_fds < shared;
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+ return state == RUNNING && nb_fds < shared;
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}
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static void nbd_export_closed(NBDExport *exp)
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--
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1.8.3.1
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