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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1724337391; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=FixiWQ3cwOxFgkWOuuQBMcavXNUKMBjsxQygjgu1SbY=; b=Vm8kddtvy+M+oWPRhc0PZY3yN73wu2UM4v9bBFEj2rxdl44qBaqPSUzcjpl/aWjJEoFGG4 AQupSX2y/2XEc5EzyAVuftX1pml6187U7i8u+4D+msofDuuQnpge+Q/xZR5JDgEhT7brMF JmPaSd7Q1lejwz2cf8MyAO5YZNX+RUA= X-MC-Unique: itsr66tRPYqkE0OEe0fdnA-1 From: Eric Blake To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, qemu-stable@nongnu.org, kwolf@redhat.com, hreitz@redhat.com, berrange@redhat.com, andrey.drobyshev@virtuozzo.com, alexander.ivanov@virtuozzo.com, den@virtuozzo.com, vsementsov@yandex-team.ru Subject: [PATCH for-9.1] nbd/server: CVE-2024-7409: Avoid use-after-free when closing server Date: Thu, 22 Aug 2024 09:35:29 -0500 Message-ID: <20240822143617.800419-2-eblake@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Commit 3e7ef738 plugged the use-after-free of the global nbd_server object, but overlooked a use-after-free of nbd_server->listener. Although this race is harder to hit, notice that our shutdown path first drops the reference count of nbd_server->listener, then triggers actions that can result in a pending client reaching the nbd_blockdev_client_closed() callback, which in turn calls qio_net_listener_set_client_func on a potentially stale object. If we know we don't want any more clients to connect, and have already told the listener socket to shut down, then we should not be trying to update the listener socket's associated function. Reproducer: > #!/usr/bin/python3 > > import os > from threading import Thread > > def start_stop(): > while 1: > os.system('virsh qemu-monitor-command VM \'{"execute": "nbd-serve= r-start", +"arguments":{"addr":{"type":"unix","data":{"path":"/tmp/nbd-sock"}}}}\'') > os.system('virsh qemu-monitor-command VM \'{"execute": "nbd-serve= r-stop"}\'') > > def nbd_list(): > while 1: > os.system('/path/to/build/qemu-nbd -L -k /tmp/nbd-sock') > > def test(): > sst =3D Thread(target=3Dstart_stop) > sst.start() > nlt =3D Thread(target=3Dnbd_list) > nlt.start() > > sst.join() > nlt.join() > > test() Fixes: CVE-2024-7409 Fixes: 3e7ef738c8 ("nbd/server: CVE-2024-7409: Close stray clients at serve= r-stop") CC: qemu-stable@nongnu.org Reported-by: Andrey Drobyshev Signed-off-by: Eric Blake Reviewed-by: Stefan Hajnoczi --- blockdev-nbd.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/blockdev-nbd.c b/blockdev-nbd.c index f73409ae494..b36f41b7c5a 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -92,10 +92,13 @@ static void nbd_accept(QIONetListener *listener, QIOCha= nnelSocket *cioc, static void nbd_update_server_watch(NBDServerData *s) { - if (!s->max_connections || s->connections < s->max_connections) { - qio_net_listener_set_client_func(s->listener, nbd_accept, NULL, NU= LL); - } else { - qio_net_listener_set_client_func(s->listener, NULL, NULL, NULL); + if (s->listener) { + if (!s->max_connections || s->connections < s->max_connections) { + qio_net_listener_set_client_func(s->listener, nbd_accept, NULL, + NULL); + } else { + qio_net_listener_set_client_func(s->listener, NULL, NULL, NULL= ); + } } } @@ -113,6 +116,7 @@ static void nbd_server_free(NBDServerData *server) */ qio_net_listener_disconnect(server->listener); object_unref(OBJECT(server->listener)); + server->listener =3D NULL; QLIST_FOREACH_SAFE(conn, &server->conns, next, tmp) { qio_channel_shutdown(QIO_CHANNEL(conn->cioc), QIO_CHANNEL_SHUTDOWN= _BOTH, NULL); --=20 2.46.0