Re: [PATCH RESEND 3] libata: if T_LENGTH is zero, dma direction should be DMA_NONE

[Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>]

On 2021/12/14 22:25, George Kennedy wrote:
> Avoid data corruption by rejecting pass-through commands where
> T_LENGTH is zero (No data is transferred) and the dma direction
> is not DMA_NONE.
> 
> Cc:<stable@xxxxxxxxxxxxxxx>
> Reported-by: syzkaller<syzkaller@xxxxxxxxxxxxxxxx>
> Signed-off-by: George Kennedy<george.kennedy@xxxxxxxxxx>
> ---
>   drivers/ata/libata-scsi.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 1b84d55..d428392 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -2859,6 +2859,12 @@ static unsigned int ata_scsi_pass_thru(struct 
> ata_queued_cmd *qc)
>           goto invalid_fld;
>       }
> 
> +    /* if T_LENGTH is zero (No data is transferred), then dir should be 
> DMA_NONE */
> +    if ((cdb[2 + cdb_offset] & 3) == 0 && scmd->sc_data_direction != 
> DMA_NONE) {
> +        fp = 2 + cdb_offset;
> +        goto invalid_fld;
> +    }
> +
>       if (ata_is_ncq(tf->protocol) && (cdb[2 + cdb_offset] & 0x3) == 0)
>           tf->protocol = ATA_PROT_NCQ_NODATA;

Why didn't you change the code as I suggested ?

Since (cdb[2 + cdb_offset] & 3) == 0 is also used on the condition below, you
can clean this up like this:

	if (!(cdb[2 + cdb_offset] & 0x3)) {
		/*
		 * When T_LENGTH is zero (No data is transferred), dir should
		 * be DMA_NONE.
		 */
		if (scmd->sc_data_direction != DMA_NONE) {
			fp = 2 + cdb_offset;
			goto invalid_fld;
		}

		if (ata_is_ncq(tf->protocol))
			tf->protocol = ATA_PROT_NCQ_NODATA;
	}


-- 
Damien Le Moal
Western Digital Research