Re: [PATCH 1/2] perf ioctl: Add check for the sample_period value

[Ravi Bangoria <ravi.bangoria@linux.ibm.com>]

On 5/13/19 2:26 PM, Peter Zijlstra wrote:
> On Mon, May 13, 2019 at 09:42:13AM +0200, Peter Zijlstra wrote:
>> On Sat, May 11, 2019 at 08:12:16AM +0530, Ravi Bangoria wrote:
>>> Add a check for sample_period value sent from userspace. Negative
>>> value does not make sense. And in powerpc arch code this could cause
>>> a recursive PMI leading to a hang (reported when running perf-fuzzer).
>>>
>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
>>> ---
>>>  kernel/events/core.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>> index abbd4b3b96c2..e44c90378940 100644
>>> --- a/kernel/events/core.c
>>> +++ b/kernel/events/core.c
>>> @@ -5005,6 +5005,9 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
>>>  	if (perf_event_check_period(event, value))
>>>  		return -EINVAL;
>>>  
>>> +	if (!event->attr.freq && (value & (1ULL << 63)))
>>> +		return -EINVAL;
>>
>> Well, perf_event_attr::sample_period is __u64. Would not be the site
>> using it as signed be the one in error?
> 
> You forgot to mention commit: 0819b2e30ccb9, so I guess this just makes
> it consistent and is fine.
> 

Yeah, I was about to reply :)