Re: [PATCH 2/8] store: Detect bad response from xenstored

[Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>]

On 14/08/2026 13:56, Owen Smith wrote:
>> From: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
>> Sent: 14 August 2026 11:20 AM
>> To: Owen Smith; win-pv-devel@xxxxxxxxxxxxxxxxxxxx
>> Subject: Re: [PATCH 2/8] store: Detect bad response from xenstored
>>
>> On 14/08/2026 12:05, Tu Dinh wrote:
>>> On 14/08/2026 09:30, Owen Smith wrote:
>>>> Detect when Header.len is larger than allowed, and fail the request.
>>>>
>>>> Assisted-by: ClaudeCode:claude-opus-4.8
>>>> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
>>>
>>> Reviewed-by: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
>>>
>>> NB: xencrsh/store.c would likely benefit from the same change.
>>>
>>>> ---
>>>>     src/xenbus/store.c | 4 ++++
>>>>     1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/src/xenbus/store.c b/src/xenbus/store.c
>>>> index 503144a..e2a0031 100644
>>>> --- a/src/xenbus/store.c
>>>> +++ b/src/xenbus/store.c
>>>> @@ -519,9 +519,13 @@ StoreReceiveResponse(
>>>>
>>>>         ASSERT(StoreVerifyHeader(&Response->Header));
>>>>
>>>> +    status = STATUS_INVALID_BUFFER_SIZE;
>>>>         if (Response->Header.len == 0)
>>>>             goto done;
>>>>
>>>> +    if (Response->Header.len >= XENSTORE_PAYLOAD_MAX)
>>
>> Never mind, shouldn't this be Response->Header.len > XENSTORE_PAYLOAD_MAX?
>>
> 
> I was thinking that a length of 4096 should fail, so there is space in the 
> buffer for a terminating null.
> 

xenstore.txt specifies that: "The payload length (len field of the 
header) is limited to 4096 (XENSTORE_PAYLOAD_MAX) in both directions". 
So my understanding is that this field should tolerate a value of 4096.

>>>> +        goto done;
>>>> +
>>>>         Response->Segment[XENBUS_STORE_RESPONSE_PAYLOAD_SEGMENT].Length = 
>>>> Response->Header.len;
>>>>         Response->Segment[XENBUS_STORE_RESPONSE_PAYLOAD_SEGMENT].Data = 
>>>> Response->Data;
>>>>
>>>
>>>
>>>



--
Ngoc Tu Dinh | Vates XCP-ng Developer

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