[Qemu-devel] [PATCH] scsi: lsi: exit infinite loop while executing script (CVE-2019-12068)

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

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

When executing script in lsi_execute_script(), the LSI scsi
adapter emulator advances 's->dsp' index to read next opcode.
This can lead to an infinite loop if the next opcode is empty.
Exit such loop after reading 10k empty opcodes.

Reported-by: Bugs SysSec <bugs-syssec@rub.de>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/scsi/lsi53c895a.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
index 10468c1ec1..c23a40525e 100644
--- a/hw/scsi/lsi53c895a.c
+++ b/hw/scsi/lsi53c895a.c
@@ -1132,7 +1132,10 @@ static void lsi_execute_script(LSIState *s)
 
     s->istat1 |= LSI_ISTAT1_SRUN;
 again:
-    insn_processed++;
+    if (++insn_processed > 10000) {
+        s->waiting = LSI_NOWAIT;
+        goto exitloop;
+    }
     insn = read_dword(s, s->dsp);
     if (!insn) {
         /* If we receive an empty opcode increment the DSP by 4 bytes
@@ -1569,6 +1572,7 @@ again:
             }
         }
     }
+exitloop:
     if (insn_processed > 10000 && s->waiting == LSI_NOWAIT) {
         /* Some windows drivers make the device spin waiting for a memory
            location to change.  If we have been executed a lot of code then
-- 
2.21.0