Re: [PATCH v2 2/8] s390/sclp: check sccb len before filling in data

[Collin Walling <walling@linux.ibm.com>]

On 6/11/20 8:01 AM, Thomas Huth wrote:
> On 16/05/2020 00.20, Collin Walling wrote:
>> The SCCB must be checked for a sufficient length before it is filled
>> with any data. If the length is insufficient, then the SCLP command
>> is suppressed and the proper response code is set in the SCCB header.
>>
>> Fixes: 832be0d8a3bb ("s390x: sclp: Report insufficient SCCB length")
>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>> ---
>>  hw/s390x/sclp.c | 22 ++++++++++------------
>>  1 file changed, 10 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index 61e2e2839c..2bd618515e 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -75,6 +75,11 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>>      int rnsize, rnmax;
>>      IplParameterBlock *ipib = s390_ipl_get_iplb();
>>  
>> +    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadInfo) + cpu_count * sizeof(CPUEntry))) {
> 
> You are using cpu_count here ...
> 
>> +        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> +        return;
>> +    }
>> +
>>      /* CPU information */
>>      prepare_cpu_entries(machine, read_info->entries, &cpu_count);
> 
> ... but it is only initialized here.
> 
> Even if you replace the code in a later patch, please fix this here,
> too, to maintain bisectability of the code.
> 
>>      read_info->entries_cpu = cpu_to_be16(cpu_count);
>> @@ -83,12 +88,6 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>>  
>>      read_info->ibc_val = cpu_to_be32(s390_get_ibc_val());
>>  
>> -    if (be16_to_cpu(sccb->h.length) <
>> -            (sizeof(ReadInfo) + cpu_count * sizeof(CPUEntry))) {
>> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> -        return;
>> -    }
>> -
>>      /* Configuration Characteristic (Extension) */
>>      s390_get_feat_block(S390_FEAT_TYPE_SCLP_CONF_CHAR,
>>                           read_info->conf_char);
>> @@ -135,17 +134,16 @@ static void sclp_read_cpu_info(SCLPDevice *sclp, SCCB *sccb)
>>      ReadCpuInfo *cpu_info = (ReadCpuInfo *) sccb;
>>      int cpu_count;
>>  
>> +    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadCpuInfo) + cpu_count * sizeof(CPUEntry))) {
> 
> dito!
> 
>> +        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> +        return;
>> +    }
>> +
>>      prepare_cpu_entries(machine, cpu_info->entries, &cpu_count);
>>      cpu_info->nr_configured = cpu_to_be16(cpu_count);
>>      cpu_info->offset_configured = cpu_to_be16(offsetof(ReadCpuInfo, entries));
>>      cpu_info->nr_standby = cpu_to_be16(0);
>>  
>> -    if (be16_to_cpu(sccb->h.length) <
>> -            (sizeof(ReadCpuInfo) + cpu_count * sizeof(CPUEntry))) {
>> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> -        return;
>> -    }
>> -
>>      /* The standby offset is 16-byte for each CPU */
>>      cpu_info->offset_standby = cpu_to_be16(cpu_info->offset_configured
>>          + cpu_info->nr_configured*sizeof(CPUEntry));
> 
>  Thanks,
>   Thomas
> 

I'll rework this patch. Thanks for the reviews!

-- 
Regards,
Collin

Stay safe and stay healthy