pxa2xx: avoid buffer overrun on incoming migration

CVE-2013-4533

s->rx_level is read from the wire and used to determine how many bytes
to subsequently read into s->rx_fifo[]. If s->rx_level exceeds the
length of s->rx_fifo[] the buffer can be overrun with arbitrary data
from the wire.

Fix this by validating rx_level against the size of s->rx_fifo.

Cc: Don Koch <dkoch@verizon.com>
Reported-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Don Koch <dkoch@verizon.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
(cherry picked from commit caa881a)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/arm/pxa2xx.c

@@ -742,7 +742,7 @@ static void pxa2xx_ssp_save(QEMUFile *f, void *opaque)
 static int pxa2xx_ssp_load(QEMUFile *f, void *opaque, int version_id)
 {
     PXA2xxSSPState *s = (PXA2xxSSPState *) opaque;
-    int i;
+    int i, v;
 
     s->enable = qemu_get_be32(f);
 
@@ -756,7 +756,11 @@ static int pxa2xx_ssp_load(QEMUFile *f, void *opaque, int version_id)
     qemu_get_8s(f, &s->ssrsa);
     qemu_get_8s(f, &s->ssacd);
 
-    s->rx_level = qemu_get_byte(f);
+    v = qemu_get_byte(f);
+    if (v < 0 || v > ARRAY_SIZE(s->rx_fifo)) {
+        return -EINVAL;
+    }
+    s->rx_level = v;
     s->rx_start = 0;
     for (i = 0; i < s->rx_level; i ++)
         s->rx_fifo[i] = qemu_get_byte(f);