scsi: check buffer length before reading scsi command

Commit Message

Paolo Bonzini June 1, 2016, 1:10 p.m. UTC

On 31/05/2016 19:53, P J P wrote:
> From: Prasad J Pandit <[e-mail]>
> 
> The 53C9X Fast SCSI Controller(FSC) comes with an internal 16-byte
> FIFO buffer. It is used to handle command and data transfer.
> Routine get_cmd() in non-DMA mode, uses 'ti_size' to read scsi
> command into a buffer. Add check to validate command length against
> buffer size to avoid any overrun.
> 
> Reported-by: Li Qiang <[e-mail]>
> Signed-off-by: Prasad J Pandit <[e-mail]>
> ---
>  hw/scsi/esp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index 60c1b28..953027a 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -98,6 +98,9 @@ static uint32_t get_cmd(ESPState *s, uint8_t *buf, uint8_t buflen)
>          s->dma_memory_read(s->dma_opaque, buf, dmalen);
>      } else {
>          dmalen = s->ti_size;
> +        if (dmalen > TI_BUFSZ) {
> +            return 0;
> +        }
>          memcpy(buf, s->ti_buf, dmalen);
>          buf[0] = buf[2] >> 5;
>      }
> 

In theory this shouldn't happen, but I agree that it is better to be
defensive.  I'm queuing this patch.

At least the following patch is needed to ensure that ti_size always
matches ti_rptr/ti_wptr (Hervé, what do you think about it? should I
resubmit it formally?).  Also, things are more complicated than
necessary due to ti_size being used for both DMA and FIFO transfers.



Paolo

Patch

diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
index c2f6f8f..6407844 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -222,7 +222,7 @@  static void write_response(ESPState *s)
     } else {
         s->ti_size = 2;
         s->ti_rptr = 0;
-        s->ti_wptr = 0;
+        s->ti_wptr = 2;
         s->rregs[ESP_RFLAGS] = 2;
     }
     esp_raise_irq(s);