Re: [Qemu-devel] [PATCH] qdev-monitor: fix segmentation fault on qdev_device_help()

[Markus Armbruster <armbru@redhat.com>]

<arei.gonglei@huawei.com> writes:

> From: Gonglei <arei.gonglei@huawei.com>
>
> Normally, qmp_device_list_properties() may return NULL when
> a device haven't special properties excpet Object and DeviceState
> properties, such as virtio-balloon-device.
>
> We just need check local_err instead of prop_list.
>
> Example:
>
> Segmentation fault (core dumped)
>
> The backtrace as below:
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00005555559af1a8 in error_get_pretty (err=0x0) at util/error.c:152
> 152         return err->msg;
> (gdb) bt
> #0  0x00005555559af1a8 in error_get_pretty (err=0x0) at util/error.c:152
> #1  0x000055555572fce9 in qdev_device_help (opts=0x5555562fdfe0) at qdev-monitor.c:210
> #2  0x000055555574a6f2 in device_help_func (opts=0x5555562fdfe0, opaque=0x0) at vl.c:2362
> #3  0x00005555559c0a33 in qemu_opts_foreach (list=0x555555dd0b40 <qemu_device_opts>, 
>     func=0x55555574a6ca <device_help_func>, opaque=0x0, abort_on_failure=0) at util/qemu-option.c:1072
> #4  0x000055555574f514 in main (argc=3, argv=0x7fffffffe218, envp=0x7fffffffe238) at vl.c:4246
>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  qdev-monitor.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/qdev-monitor.c b/qdev-monitor.c
> index fb9ee24..5ec6606 100644
> --- a/qdev-monitor.c
> +++ b/qdev-monitor.c
> @@ -206,7 +206,7 @@ int qdev_device_help(QemuOpts *opts)
>      }
>  
>      prop_list = qmp_device_list_properties(driver, &local_err);
> -    if (!prop_list) {
> +    if (local_err) {
>          error_printf("%s\n", error_get_pretty(local_err));
>          error_free(local_err);
>          return 1;

Doesn't this leak prop_list when local_err && prop_list?

Returning both a value in need of destruction and an error object is at
least highly unusual, and probably plain wrong.

Should qmp_device_list_properties() return NULL when it sets an error?