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102 lines
3.6 KiB
102 lines
3.6 KiB
From 3732f1491d8981e85f699fcd125d903aba77fa32 Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Thu, 22 Aug 2024 09:35:29 -0500
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Subject: [PATCH] nbd/server: CVE-2024-7409: Avoid use-after-free when closing
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server
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RH-Author: Eric Blake <eblake@redhat.com>
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RH-MergeRequest: 267: nbd/server: CVE-2024-7409: Avoid use-after-free when closing server
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RH-Jira: RHEL-52599
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Hanna Czenczek <hreitz@redhat.com>
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RH-Commit: e7d52e5d1372eaec00325d4854772ee78fe650b7 (ebblake/centos-qemu-kvm)
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Commit 3e7ef738 plugged the use-after-free of the global nbd_server
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object, but overlooked a use-after-free of nbd_server->listener.
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Although this race is harder to hit, notice that our shutdown path
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first drops the reference count of nbd_server->listener, then triggers
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actions that can result in a pending client reaching the
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nbd_blockdev_client_closed() callback, which in turn calls
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qio_net_listener_set_client_func on a potentially stale object.
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If we know we don't want any more clients to connect, and have already
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told the listener socket to shut down, then we should not be trying to
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update the listener socket's associated function.
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Reproducer:
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> #!/usr/bin/python3
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>
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> import os
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> from threading import Thread
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>
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> def start_stop():
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> while 1:
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> os.system('virsh qemu-monitor-command VM \'{"execute": "nbd-server-start",
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+"arguments":{"addr":{"type":"unix","data":{"path":"/tmp/nbd-sock"}}}}\'')
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> os.system('virsh qemu-monitor-command VM \'{"execute": "nbd-server-stop"}\'')
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>
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> def nbd_list():
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> while 1:
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> os.system('/path/to/build/qemu-nbd -L -k /tmp/nbd-sock')
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>
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> def test():
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> sst = Thread(target=start_stop)
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> sst.start()
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> nlt = Thread(target=nbd_list)
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> nlt.start()
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>
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> sst.join()
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> nlt.join()
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>
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> test()
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Fixes: CVE-2024-7409
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Fixes: 3e7ef738c8 ("nbd/server: CVE-2024-7409: Close stray clients at server-stop")
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CC: qemu-stable@nongnu.org
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Reported-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
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Signed-off-by: Eric Blake <eblake@redhat.com>
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Message-ID: <20240822143617.800419-2-eblake@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 3874f5f73c441c52f1c699c848d463b0eda01e4c)
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Jira: https://issues.redhat.com/browse/RHEL-52599
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Signed-off-by: Eric Blake <eblake@redhat.com>
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---
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blockdev-nbd.c | 12 ++++++++----
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1 file changed, 8 insertions(+), 4 deletions(-)
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diff --git a/blockdev-nbd.c b/blockdev-nbd.c
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index f73409ae49..b36f41b7c5 100644
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--- a/blockdev-nbd.c
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+++ b/blockdev-nbd.c
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@@ -92,10 +92,13 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
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static void nbd_update_server_watch(NBDServerData *s)
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{
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- if (!s->max_connections || s->connections < s->max_connections) {
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- qio_net_listener_set_client_func(s->listener, nbd_accept, NULL, NULL);
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- } else {
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- qio_net_listener_set_client_func(s->listener, NULL, NULL, NULL);
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+ if (s->listener) {
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+ if (!s->max_connections || s->connections < s->max_connections) {
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+ qio_net_listener_set_client_func(s->listener, nbd_accept, NULL,
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+ NULL);
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+ } else {
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+ qio_net_listener_set_client_func(s->listener, NULL, NULL, NULL);
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+ }
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}
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}
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@@ -113,6 +116,7 @@ static void nbd_server_free(NBDServerData *server)
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*/
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qio_net_listener_disconnect(server->listener);
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object_unref(OBJECT(server->listener));
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+ server->listener = NULL;
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QLIST_FOREACH_SAFE(conn, &server->conns, next, tmp) {
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qio_channel_shutdown(QIO_CHANNEL(conn->cioc), QIO_CHANNEL_SHUTDOWN_BOTH,
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NULL);
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--
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2.39.3
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