xen/CVE-2016-4439-qemut-scsi-esp-OOB-write-while-writing-to-cmdbuf-in-esp_reg_write.patch

References: bsc#980716 CVE-2016-4439 

The 53C9X Fast SCSI Controller(FSC) comes with an internal 16-byte
FIFO buffer. It is used to handle command and data transfer. While
writing to this command buffer 's->cmdbuf[TI_BUFSZ=16]', a check
was missing to validate input length. Add check to avoid OOB write
access.

Fixes CVE-2016-4439
Reported-by: Li Qiang <address@hidden>

Signed-off-by: Prasad J Pandit <address@hidden>
---
 hw/scsi/esp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: xen-4.4.4-testing/tools/qemu-xen-traditional-dir-remote/hw/esp.c
===================================================================
--- xen-4.4.4-testing.orig/tools/qemu-xen-traditional-dir-remote/hw/esp.c
+++ xen-4.4.4-testing/tools/qemu-xen-traditional-dir-remote/hw/esp.c
@@ -471,7 +471,11 @@ static void esp_mem_writeb(void *opaque,
         break;
     case ESP_FIFO:
         if (s->do_cmd) {
-            s->cmdbuf[s->cmdlen++] = val & 0xff;
+            if (s->cmdlen < TI_BUFSZ) {
+                s->cmdbuf[s->cmdlen++] = val & 0xff;
+            } else {
+                ESP_ERROR("fifo overrun\n");
+            }
         } else if (s->ti_size == TI_BUFSZ - 1) {
             ESP_ERROR("fifo overrun\n");
         } else {