Re: [PATCH] qemuMonitorUnregister: Fix use-after-free of mon->watch

qemuMonitorUnregister will be called in multiple threads (e.g. threads in rpc worker pool and the vm event thread). In some cases, it isn't protected by the monitor lock, which may lead to call g_source_unref more than one time and a use-after-free problem eventually. To avoid similar problem in the future, use g_atomic_pointer_compare_and_exchange instead of adding a lock in the missing cases. Signed-off-by: Peng Liang <liangpeng10(a)huawei.com&gt; --- src/qemu/qemu_monitor.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c index 0476d606f553..f4d05cd951c2 100644 --- a/src/qemu/qemu_monitor.c +++ b/src/qemu/qemu_monitor.c @@ -853,10 +853,11 @@ qemuMonitorRegister(qemuMonitorPtr mon) void qemuMonitorUnregister(qemuMonitorPtr mon) { - if (mon->watch) { - g_source_destroy(mon->watch); - g_source_unref(mon->watch); - mon->watch = NULL; + GSource *watch = mon->watch; + + if (watch && g_atomic_pointer_compare_and_exchange(&mon->watch, watch, NULL)) { + g_source_destroy(watch); + g_source_unref(watch); } }