[Qemu-devel] [PATCH] scsi: check page count while initialising descriptor rings

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

Vmware Paravirtual SCSI emulation uses command descriptors to
process SCSI commands. These descriptors come with their ring
buffers. A guest could set the page count for these rings to
be zero, leading to an infinite loop. Add check to avoid it.

Reported-by: Tom Victor <vv474172261@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/scsi/vmw_pvscsi.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
index 5116f4a..68c1a00 100644
--- a/hw/scsi/vmw_pvscsi.c
+++ b/hw/scsi/vmw_pvscsi.c
@@ -160,8 +160,10 @@ pvscsi_ring_init_data(PVSCSIRingInfo *m, PVSCSICmdDescSetupRings *ri)
     uint32_t req_ring_size, cmp_ring_size;
     m->rs_pa = ri->ringsStatePPN << VMW_PAGE_SHIFT;
 
-    if ((ri->reqRingNumPages > PVSCSI_SETUP_RINGS_MAX_NUM_PAGES)
-        || (ri->cmpRingNumPages > PVSCSI_SETUP_RINGS_MAX_NUM_PAGES)) {
+    if (!ri->reqRingNumPages
+        || ri->reqRingNumPages > PVSCSI_SETUP_RINGS_MAX_NUM_PAGES
+        || !ri->cmpRingNumPages
+        || ri->cmpRingNumPages > PVSCSI_SETUP_RINGS_MAX_NUM_PAGES) {
         return -1;
     }
     req_ring_size = ri->reqRingNumPages * PVSCSI_MAX_NUM_REQ_ENTRIES_PER_PAGE;
-- 
2.5.5