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To: Bruce Richardson <bruce.richardson@intel.com>
Cc: David Hunt <david.hunt@intel.com>, dev@dpdk.org, stable@dpdk.org
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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
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Date: Fri, 26 Apr 2019 13:47:41 +0100
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Subject: Re: [dpdk-dev] [PATCH v2] examples/vm_power_manager: fix string
 null termination
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On 26-Apr-19 1:31 PM, Bruce Richardson wrote:
> On Fri, Apr 26, 2019 at 12:56:08PM +0100, Burakov, Anatoly wrote:
>> On 26-Apr-19 12:24 PM, David Hunt wrote:
>>> coverity complains about a null-termination after a read,
>>> so we terminate after exiting the do-while loop. The position
>>> is conditional on whether idx is within the buffer or at the
>>> end of the buffer.
>>>
>>> Coverity issue: 337680
>>> Fixes: a63504a90f ("examples/power: add JSON string handling")
>>> CC: stable@dpdk.org
>>>
>>> Signed-off-by: David Hunt <david.hunt@intel.com>
>>>
>>> ---
>>> v2:
>>>      * Move null termination outside of do-while.
>>> ---
>>>    examples/vm_power_manager/channel_monitor.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/examples/vm_power_manager/channel_monitor.c b/examples/vm_power_manager/channel_monitor.c
>>> index 971e4f2bc..03fdcd15a 100644
>>> --- a/examples/vm_power_manager/channel_monitor.c
>>> +++ b/examples/vm_power_manager/channel_monitor.c
>>> @@ -822,6 +822,8 @@ read_json_packet(struct channel_info *chan_info)
>>>    				break;
>>>    		} while (indent > 0);
>>> +		json_data[idx + (idx < MAX_JSON_STRING_LEN - 1)] = '\0';
>>> +
>>
>> I don't think you need this complicated logic here. You start at idx = 0, so
>> even if you receive 0 bytes, you'll terminate buffer at index 0. You also
>> break when idx reaches (MAX_JSON_STRING_LEN - 1), so it's also safe to do
>> json_data[idx] after the loop. In all other cases, you still increment idx
>> before breaking out (e.g. when reaching indent == 0), so it's also safe to
>> do json_data[idx] in those cases.
>>
> +1 to that.
> 
> An alternative and simpler option might be to memset the who array to zero
> before you start anyway.

That'll cost us few extra cycles on a non-performance critical path full 
of syscalls, surely we can't have that! :)

> 
> /Bruce
> 


-- 
Thanks,
Anatoly

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 <339cb6ac-9c56-b9cb-28e8-950ad2cd70b4@intel.com>
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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
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Date: Fri, 26 Apr 2019 13:47:41 +0100
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Subject: Re: [dpdk-dev] [PATCH v2] examples/vm_power_manager: fix string
 null termination
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On 26-Apr-19 1:31 PM, Bruce Richardson wrote:
> On Fri, Apr 26, 2019 at 12:56:08PM +0100, Burakov, Anatoly wrote:
>> On 26-Apr-19 12:24 PM, David Hunt wrote:
>>> coverity complains about a null-termination after a read,
>>> so we terminate after exiting the do-while loop. The position
>>> is conditional on whether idx is within the buffer or at the
>>> end of the buffer.
>>>
>>> Coverity issue: 337680
>>> Fixes: a63504a90f ("examples/power: add JSON string handling")
>>> CC: stable@dpdk.org
>>>
>>> Signed-off-by: David Hunt <david.hunt@intel.com>
>>>
>>> ---
>>> v2:
>>>      * Move null termination outside of do-while.
>>> ---
>>>    examples/vm_power_manager/channel_monitor.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/examples/vm_power_manager/channel_monitor.c b/examples/vm_power_manager/channel_monitor.c
>>> index 971e4f2bc..03fdcd15a 100644
>>> --- a/examples/vm_power_manager/channel_monitor.c
>>> +++ b/examples/vm_power_manager/channel_monitor.c
>>> @@ -822,6 +822,8 @@ read_json_packet(struct channel_info *chan_info)
>>>    				break;
>>>    		} while (indent > 0);
>>> +		json_data[idx + (idx < MAX_JSON_STRING_LEN - 1)] = '\0';
>>> +
>>
>> I don't think you need this complicated logic here. You start at idx = 0, so
>> even if you receive 0 bytes, you'll terminate buffer at index 0. You also
>> break when idx reaches (MAX_JSON_STRING_LEN - 1), so it's also safe to do
>> json_data[idx] after the loop. In all other cases, you still increment idx
>> before breaking out (e.g. when reaching indent == 0), so it's also safe to
>> do json_data[idx] in those cases.
>>
> +1 to that.
> 
> An alternative and simpler option might be to memset the who array to zero
> before you start anyway.

That'll cost us few extra cycles on a non-performance critical path full 
of syscalls, surely we can't have that! :)

> 
> /Bruce
> 


-- 
Thanks,
Anatoly