[PATCH v2 1/3] megasas: use unsigned type for reply_queue_head and check index

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

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

A guest user may set 'reply_queue_head' field of MegasasState to
a negative value. Later in 'megasas_lookup_frame' it is used to
index into s->frames[] array. Use unsigned type to avoid OOB
access issue.

Also check that 'index' value stays within s->frames[] bounds
through the while() loop in 'megasas_lookup_frame' to avoid OOB
access.

Reported-by: Ren Ding <rding@gatech.edu>
Reported-by: Hanqing Zhao <hanqing@gatech.edu>
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/scsi/megasas.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Update v1 -> v2: fix OOB access when index > MEGASAS_MAX_FRAMES(=2048)
 -> https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg03131.html

diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index af18c88b65..6ce598cd69 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -112,7 +112,7 @@ typedef struct MegasasState {
     uint64_t reply_queue_pa;
     void *reply_queue;
     int reply_queue_len;
-    int reply_queue_head;
+    uint16_t reply_queue_head;
     int reply_queue_tail;
     uint64_t consumer_pa;
     uint64_t producer_pa;
@@ -445,7 +445,7 @@ static MegasasCmd *megasas_lookup_frame(MegasasState *s,
 
     index = s->reply_queue_head;
 
-    while (num < s->fw_cmds) {
+    while (num < s->fw_cmds && index < MEGASAS_MAX_FRAMES) {
         if (s->frames[index].pa && s->frames[index].pa == frame) {
             cmd = &s->frames[index];
             break;
-- 
2.25.4