scsi: pvscsi: limit process IO loop to ring size

Vmware Paravirtual SCSI emulator while processing IO requests
could run into an infinite loop if 'pvscsi_ring_pop_req_descr'
always returned positive value. Limit IO loop to the ring size.

Cc: qemu-stable@nongnu.org
Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <1473845952-30785-1-git-send-email-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
index babac5a..a5ce7de 100644 (file)
--- a/hw/scsi/vmw_pvscsi.c
+++ b/hw/scsi/vmw_pvscsi.c
@@ -247,8 +247,11 @@ static hwaddr
 pvscsi_ring_pop_req_descr(PVSCSIRingInfo *mgr)
 {
     uint32_t ready_ptr = RS_GET_FIELD(mgr, reqProdIdx);
+    uint32_t ring_size = PVSCSI_MAX_NUM_PAGES_REQ_RING
+                            * PVSCSI_MAX_NUM_REQ_ENTRIES_PER_PAGE;
 
-    if (ready_ptr != mgr->consumed_ptr) {
+    if (ready_ptr != mgr->consumed_ptr
+        && ready_ptr - mgr->consumed_ptr < ring_size) {
         uint32_t next_ready_ptr =
             mgr->consumed_ptr++ & mgr->txr_len_mask;
         uint32_t next_ready_page =