On 05.03.21 15:46, Ian Jackson wrote:
> Jürgen Groß writes ("Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters"):
>> On 05.03.21 15:37, Ian Jackson wrote:
>>> Jürgen Groß writes ("Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters"):
>>>> This is the max number of 0 delimited string parameters. Especially the
>>>> stubdom case needs a binary blob (with length, of course) as parameter,
>>>> and the number of 0 bytes in this data is just limited by the allowed
>>>> payload length.
>>>>
>>>> See the comment in line 111 of xenstored_control.c.
>>>
>>> AFAICT this "live-update" command is variadic.  So why is this
>>> parameter set here it all then ?
>>
>> In order to avoid allocating an array for 4000 arguments when there
>> are only 5 which need to be treated as strings.
> 
> So this parameter is doing two jobs: 1. enabling non-variadic commands
> to take binary input; 2. preventing variadic commands from allocating
> unbounded memory.
> 
> The problem with this is that in case 1 exceeding the value is normal
> and the final argument is binary data; whereas in case 2 glomming
> together the arguments together with zeroes is wrong and potentially
> hazrdous.
> 
> I suggest we solve problem 2 by imposing a higher fixed (for all
> commands, variadic or not) limit (20 or something) which causes errors
> when exceeded, rather than silent argument misinterpretation.

Patches welcome.


Juergen