Re: [RFC PATCH-for-6.2 v3] qdev-monitor: Only allow full --global <driver>.<property>=<val> option

[Markus Armbruster <armbru@redhat.com>]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> When not all fields of the --global option are provided,
> QEMU might crash:
>
>   $ qemu-system-x86_64 -global driver=isa-fdc
>   qemu-system-x86_64: ../../devel/qemu/qapi/string-input-visitor.c:394:
>   string_input_visitor_new: Assertion `str' failed.
>   Aborted (core dumped)
>
> Fix by only allowing --global with all 3 fields:
>
>   $ qemu-system-x86_64 -global driver=isa-fdc
>   Invalid 'global' option format. It must be provided as:
>     --global <driver>.<property>=<value>
>
> Reported-by: Thomas Huth <thuth@redhat.com>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/604
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> v3: Change qemu_global_option (Markus)
>
> Supersedes: <20211119122911.365036-1-philmd@redhat.com>
> ---
>  softmmu/qdev-monitor.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> index 01f3834db57..558272b147c 100644
> --- a/softmmu/qdev-monitor.c
> +++ b/softmmu/qdev-monitor.c
> @@ -1029,13 +1029,10 @@ int qemu_global_option(const char *str)
>          qemu_opt_set(opts, "value", str + offset + 1, &error_abort);
>          return 0;
>      }
> +    printf("Invalid 'global' option format. It must be provided as:\n");
> +    printf("  --global <driver>.<property>=<value>\n");
>  
> -    opts = qemu_opts_parse_noisily(&qemu_global_opts, str, false);
> -    if (!opts) {
> -        return -1;
> -    }
> -
> -    return 0;
> +    return -1;
>  }
>  
>  bool qmp_command_available(const QmpCommand *cmd, Error **errp)

This drops a documented part of the external interface:

    $ qemu-system-x86_64 -help | grep -C 1 global
                    i.e. -set drive.$id.file=/path/to/image
    -global driver.property=value
--> -global driver=driver,property=property,value=value
                    set a global default for a driver property
    -boot [order=drives][,once=drives][,menu=on|off]

It goes back to commit 3751d7c43f "vl: allow full-blown QemuOpts syntax
for -global", v2.4.0.

The appropriate fix is to check @opts for presence of all three
parameters.