[Qemu-devel] [PATCH] scsi: check buffer length before reading scsi command

[Qemu-devel] [PATCH] scsi: check buffer length before reading scsi command

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

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 <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 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;
     }
-- 
2.5.5

Re: [Qemu-devel] [PATCH] scsi: check buffer length before reading scsi command

[Paolo Bonzini]

On 31/05/2016 19:53, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> 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 <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  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.

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);


Paolo