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

[Gonglei (Arei)]

> From: Markus Armbruster [mailto:address@hidden
> Sent: Tuesday, September 16, 2014 3:28 PM
> Subject: Re: [Qemu-devel] [PATCH] qdev-monitor: fix segmentation fault on
> qdev_device_help()
> 
> <address@hidden> writes:
> 
> > From: Gonglei <address@hidden>
> >
> > 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 <address@hidden>
> > ---
> >  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?
> 
No, it will not happen this situation.

> 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?

Yes, it was.

Best regards,
-Gonglei