scsi: megasas: check 'read_queue_head' index value

While doing MegaRAID SAS controller command frame lookup, routine
'megasas_lookup_frame' uses 'read_queue_head' value as an index
into 'frames[MEGASAS_MAX_FRAMES=2048]' array. Limit its value
within array bounds to avoid any OOB access.
Reported-by: NLi Qiang <liqiang6-s@360.cn>
Signed-off-by: NPrasad J Pandit <pjp@fedoraproject.org>
Message-Id: <1464179110-18593-1-git-send-email-ppandit@redhat.com>
Reviewed-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi/megasas.c

@@ -650,7 +650,9 @@ static int megasas_init_firmware(MegasasState *s, MegasasCmd *cmd)
     pa_hi = le32_to_cpu(initq->pi_addr_hi);
     s->producer_pa = ((uint64_t) pa_hi << 32) | pa_lo;
     s->reply_queue_head = ldl_le_pci_dma(pcid, s->producer_pa);
+    s->reply_queue_head %= MEGASAS_MAX_FRAMES;
     s->reply_queue_tail = ldl_le_pci_dma(pcid, s->consumer_pa);
+    s->reply_queue_tail %= MEGASAS_MAX_FRAMES;
     flags = le32_to_cpu(initq->flags);
     if (flags & MFI_QUEUE_FLAG_CONTEXT64) {
         s->flags |= MEGASAS_MASK_USE_QUEUE64;