Re: [PATCH v3 20/26] x86: Fix x86_cpu_new() error handling

[Paolo Bonzini]

On 02/07/20 06:51, Markus Armbruster wrote:
> Igor, Paolo, you showed me the error in v2.  Could you have a look at
> this revision?
> 
> Markus Armbruster <armbru@redhat.com> writes:
> 
>> The Error ** argument must be NULL, &error_abort, &error_fatal, or a
>> pointer to a variable containing NULL.  Passing an argument of the
>> latter kind twice without clearing it in between is wrong: if the
>> first call sets an error, it no longer points to NULL for the second
>> call.
>>
>> x86_cpu_new() is wrong that way: it passes &local_err to
>> object_property_set_uint() without checking it, and then to
>> qdev_realize().  If both fail, we'll trip error_setv()'s assertion.
>> To assess the bug's impact, we'd need to figure out how to make both
>> calls fail.  Too much work for ignorant me, sorry.
>>
>> Fix by checking for failure right away.
>>
>> Cc: Igor Mammedov <imammedo@redhat.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Richard Henderson <rth@twiddle.net>
>> Cc: Eduardo Habkost <ehabkost@redhat.com>
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>>  hw/i386/x86.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
>> index 34229b45c7..93f7371a56 100644
>> --- a/hw/i386/x86.c
>> +++ b/hw/i386/x86.c
>> @@ -118,14 +118,16 @@ uint32_t x86_cpu_apic_id_from_index(X86MachineState 
>> *x86ms,
>>  
>>  void x86_cpu_new(X86MachineState *x86ms, int64_t apic_id, Error **errp)
>>  {
>> -    Object *cpu = NULL;
>>      Error *local_err = NULL;
>> -
>> -    cpu = object_new(MACHINE(x86ms)->cpu_type);
>> +    Object *cpu = object_new(MACHINE(x86ms)->cpu_type);
>>  
>>      object_property_set_uint(cpu, apic_id, "apic-id", &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>>      qdev_realize(DEVICE(cpu), NULL, &local_err);
>>  
>> +out:
>>      object_unref(cpu);
>>      error_propagate(errp, local_err);
>>  }
> 

Yes, this looks good.  Thanks!

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo