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*From*: 	Paolo Bonzini
*Subject*: 	Re: [Qemu-devel] [PATCH] scsi: check buffer length before
reading scsi command
*Date*: 	Wed, 1 Jun 2016 15:10:16 +0200
*User-agent*: 	Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
Thunderbird/45.1.0

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On 31/05/2016 19:53, P J P wrote:
>/ From: Prasad J Pandit <address@hidden>/
>/ /
>/ 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 <address@hidden>/
>/ Signed-off-by: Prasad J Pandit <address@hidden>/
>/ ---/
>/  hw/scsi/esp.c | 3 +++/
>/  1 file changed, 3 insertions(+)/
>/ /
>/ diff --git a/tools/qemu-xen/hw/scsi/esp.c b/tools/qemu-xen/hw/scsi/esp.c/
>/ index 60c1b28..953027a 100644/
>/ --- a/tools/qemu-xen/hw/scsi/esp.c/
>/ +++ b/tools/qemu-xen/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/tools/qemu-xen/hw/scsi/esp.c b/tools/qemu-xen/hw/scsi/esp.c
index c2f6f8f..6407844 100644
--- a/tools/qemu-xen/hw/scsi/esp.c
+++ b/tools/qemu-xen/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);