On 2021/08/19 18:30, Niklas Cassel wrote:
> On Thu, Aug 19, 2021 at 04:37:50PM +0900, Damien Le Moal wrote:
>> The allocation length field of the MODE SENSE 10 command is 16-bits,
>> occupying bytes 7 and 8 of the CDB. With this command, access to mode
>> pages larger than 255 bytes is thus possible. Make sure that
>> scsi_mode_sense() code reflects this by initializing the allocation
>> length field using put_unaligned_be16() instead of directly setting
>> only byte 8 of the CDB with the buffer length.
>>
>> While at it, also fix the folowing:
>> * use get_unaligned_be16() to retrieve the mode data length and block
>> descriptor length fields of the mode sense reply header instead of
>> using an open coded calculation.
>> * Fix the kdoc dbd argument explanation: the DBD bit stands for
>> Disable Block Descriptor, which is the opposite of what the dbd
>> argument description was.
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
>> ---
>> drivers/scsi/scsi_lib.c | 9 ++++-----
>> 1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index 7456a26aef51..92db00d81733 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -2070,7 +2070,7 @@ EXPORT_SYMBOL_GPL(scsi_mode_select);
>> /**
>> * scsi_mode_sense - issue a mode sense, falling back from 10 to six bytes if necessary.
>> * @sdev: SCSI device to be queried
>> - * @dbd: set if mode sense will allow block descriptors to be returned
>> + * @dbd: set to prevent mode sense from returning block descriptors
>> * @modepage: mode page being requested
>> * @buffer: request buffer (may not be smaller than eight bytes)
>> * @len: length of request buffer.
>> @@ -2112,7 +2112,7 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
>> len = 8;
>>
>> cmd[0] = MODE_SENSE_10;
>> - cmd[8] = len;
>> + put_unaligned_be16(len, &cmd[7]);
>> header_length = 8;
>> } else {
>> if (len < 4)
>> @@ -2166,12 +2166,11 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
>> data->longlba = 0;
>> data->block_descriptor_length = 0;
>> } else if (use_10_for_ms) {
>> - data->length = buffer[0]*256 + buffer[1] + 2;
>> + data->length = get_unaligned_be16(&buffer[0]) + 2;
>> data->medium_type = buffer[2];
>> data->device_specific = buffer[3];
>> data->longlba = buffer[4] & 0x01;
>> - data->block_descriptor_length = buffer[6]*256
>> - + buffer[7];
>> + data->block_descriptor_length = get_unaligned_be16(&buffer[6]);
>> } else {
>> data->length = buffer[0] + 1;
>> data->medium_type = buffer[1];
>
> (Nit:
> When the subject contains "fix", I think that people automatically look
> for a Fixes-tag. However, AFAIK, there isn't a caller that sends in a
> length > 1 byte. So a slightly better subject might have been:
> "scsi: allow scsi_mode_sense() to read more than 255 bytes")
Indeed, that is better.
Martin,
Can you fix that up ? Or should I resend ?
There is also the fact that the argument len is not being checked against 255.
So if the device does not have use_10_for_ms set, weird things can happen.
I did not add the check because this code has been like this since a long time
and no problem is being reported...
>
> Reviewed-by: Niklas Cassel <niklas.cassel@xxxxxxx>
>
--
Damien Le Moal
Western Digital Research
