------------------------------------------------------------------------
*From*: 	P J P
*Subject*: 	[Qemu-devel] [PATCH 2/2] scsi: check dma length before
reading scsi command(CVE-2016-4441)
*Date*: 	Thu, 19 May 2016 16:09:31 +0530

------------------------------------------------------------------------

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() uses DMA to read scsi commands into this buffer.
Add check to validate DMA length against buffer size to avoid any
overrun.

Fixes CVE-2016-4441
Reported-by: Li Qiang <address@hidden>

Signed-off-by: Prasad J Pandit <address@hidden>
---
 hw/scsi/esp.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/qemu-xen-traditional/hw/esp.c b/tools/qemu-xen-traditional/hw/esp.c
index 01497e6..591c817 100644
--- a/tools/qemu-xen-traditional/hw/esp.c
+++ b/tools/qemu-xen-traditional/hw/esp.c
@@ -82,7 +82,7 @@ void esp_request_cancelled(SCSIRequest *req)
     }
 }
 
-static uint32_t get_cmd(ESPState *s, uint8_t *buf)
+static uint32_t get_cmd(ESPState *s, uint8_t *buf, uint8_t buflen)
 {
     uint32_t dmalen;
     int target;
@@ -92,6 +92,9 @@ static uint32_t get_cmd(ESPState *s, uint8_t *buf)
     target = s->wregs[ESP_WBUSID] & BUSID_DID;
     if (s->dma) {
         dmalen = s->rregs[ESP_TCLO] | (s->rregs[ESP_TCMID] << 8);
+        if (dmalen > buflen) {
+            return 0;
+        }
         s->dma_memory_read(s->dma_opaque, buf, dmalen);
     } else {
         dmalen = s->ti_size;
@@ -166,7 +169,7 @@ static void handle_satn(ESPState *s)
     uint8_t buf[32];
     int len;
 
-    len = get_cmd(s, buf);
+    len = get_cmd(s, buf, sizeof(buf));
     if (len)
         do_cmd(s, buf);
 }
@@ -192,7 +195,7 @@ static void handle_satn_stop(ESPState *s)
 
 static void handle_satn_stop(ESPState *s)
 {
-    s->cmdlen = get_cmd(s, s->cmdbuf);
+    s->cmdlen = get_cmd(s, s->cmdbuf, sizeof(s->cmdbuf));
     if (s->cmdlen) {
         DPRINTF("Set ATN & Stop: cmdlen %d\n", s->cmdlen);
         s->do_cmd = 1;
-- 
2.5.5