Re: [PATCH] vl: Fix an assert failure in error path

[Peng Liang]

On 6/10/2021 3:32 PM, Markus Armbruster wrote:
> Peng Liang <liangpeng10@huawei.com> writes:
> 
>> On 6/9/2021 8:15 PM, Daniel P. Berrangé wrote:
>>> On Wed, Jun 09, 2021 at 02:09:47PM +0200, Markus Armbruster wrote:
>>>> Paolo Bonzini <pbonzini@redhat.com> writes:
>>>>
>>>>> On 10/06/21 10:47, Zhenzhong Duan wrote:
>>>>>> Based on the description of error_setg(), the local variable err in
>>>>>> qemu_maybe_daemonize() should be initialized to NULL.
>>>>>> Without fix, the uninitialized *errp triggers assert failure which
>>>>>> doesn't show much valuable information.
>>>>>> Before the fix:
>>>>>> qemu-system-x86_64: ../util/error.c:59: error_setv: Assertion `*errp == 
>>>>>> NULL' failed.
>>>>>> After fix:
>>>>>> qemu-system-x86_64: cannot create PID file: Cannot open pid file: 
>>>>>> Permission denied
>>>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>>>> ---
>>>>>>   softmmu/vl.c | 2 +-
>>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>> diff --git a/softmmu/vl.c b/softmmu/vl.c
>>>>>> index 326c1e9080..feb4d201f3 100644
>>>>>> --- a/softmmu/vl.c
>>>>>> +++ b/softmmu/vl.c
>>>>>> @@ -2522,7 +2522,7 @@ static void qemu_process_help_options(void)
>>>>>>     static void qemu_maybe_daemonize(const char *pid_file)
>>>>>>   {
>>>>>> -    Error *err;
>>>>>> +    Error *err = NULL;
>>>>
>>>> Common mistake, I'm afraid.
>>>
>>> Initializing isn't likely to be a performance impact, so I'd think
>>> we should make 'checkpatch.pl' complain about any 'Error *' variable
>>> that is not initialized to NULL, as a safety net, even if not technically
>>> required in some cases.
>>>
>>> Regards,
>>> Daniel
>>>
>>
>> Hi,
>> Could we add a coccinelle script to check (and fix) these problems?  e.g.:
> 
> Coccinelle is good for finding and fixing instances of bad patterns that
> have crept in.  checkpatch is good for keeping them out.  Both has its
> uses.
> 
>> @ r @
>> identifier id;
>> @@
>>   Error *id
>> + = NULL
>>   ;
>>
>> Using this script, I found that local variable err in
>> qemu_init_subsystems is not initialized to NULL too.
> 
> Crash bug, broken in commit efd7ab22fb "vl: extract
> qemu_init_subsystems", v6.0.0.  Care to submit a fix?

Have sent :)

> 
>>                                                       The script is not
>> prefect though, it will initialize all global/static 'Error *' variables
>> and all local 'Error *' variables in util/error.c to NULL, which is
>> unnecessary.
> 
> Excluding util/error.c is easy once you know how to:
> 
>     @ depends on !(file in "util/error.c")@
>     identifier id;
>     @@
>     ...
> 
> Excluding variable definitions with static storage duraction shouldn't
> be too hard, either.  If Coccinelle is sufficiently clever, adding
> keyword auto suffices.  Else, try matching keyword static separately,
> like so:
> 
>     (
>         static Error *id;
>     |
>     -   Error *id;
>     +   Error *id = NULL;
>     )
> 
> Completely untested.
> 

Thanks for your improvement!

Thanks,
Peng