From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Wed, 12 Oct 2016 11:28:08 +0530
Subject: [PATCH] char: serial: check divider value against baud base

16550A UART device uses an oscillator to generate frequencies
(baud base), which decide communication speed. This speed could
be changed by dividing it by a divider. If the divider is
greater than the baud base, speed is set to zero, leading to a
divide by zero error. Add check to avoid it.

Reported-by: Huawei PSIRT <psirt@huawei.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <1476251888-20238-1-git-send-email-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 3592fe0c919cf27a81d8e9f9b4f269553418bb01)
---
 hw/char/serial.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 6d815b5..3998131 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -152,8 +152,9 @@ static void serial_update_parameters(SerialState *s)
     int speed, parity, data_bits, stop_bits, frame_size;
     QEMUSerialSetParams ssp;
 
-    if (s->divider == 0)
+    if (s->divider == 0 || s->divider > s->baudbase) {
         return;
+    }
 
     /* Start bit. */
     frame_size = 1;