hw/usb: Fix buffer overflow in do_token_setup

Store calculated setup_len in a local variable, verify it, and only
write it to the struct (USBDevice->setup_len) in case it passed the
sanity checks.

This prevent other code (do_token_{in,out} functions specifically)
from working with invalid USBDevice->setup_len values and overruning
the USBDevice->setup_buf[] buffer.
Fixes: CVE-2020-14364
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw-usb-core-fix-buffer-overflow.patch

@@ -0,0 +1,46 @@
+hw-usb-core-fix-buffer-overflow
+
+From 18ad0451f113ffc3a2ff59c059d189cca1e42842 Mon Sep 17 00:00:00 2001
+From: root <root@localhost.localdomain>
+Date: Wed, 19 Aug 2020 17:04:04 +0800
+Subject: [PATCH] hw/usb/core.c fix buffer overflow
+
+Store calculated setup_len in a local variable, verify it,
+ and only write it to the struct (USBDevice->setup_len) in case it passed the
+ sanity checks.
+
+This prevents other code (do_token_{in,out} function specifically)
+from working with invalid USBDevice->setup_len values and overruning
+the USBDevice->setup_buf[] buffer.
+Store
+Fixes: CVE-2020-14364
+Signed-off-by: Gred Hoffman <kraxel@redhat.com>
+---
+ hw/usb/core.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/hw/usb/core.c b/hw/usb/core.c
+index 5abd128b..12342f13 100644
+--- a/hw/usb/core.c
++++ b/hw/usb/core.c
+@@ -144,6 +144,8 @@ static void do_token_setup(USBDevice *s, USBPacket *p)
+                 "usb_generic_handle_packet: ctrl buffer too small (%d > %zu)\n",
+                 s->setup_len, sizeof(s->data_buf));
+         p->status = USB_RET_STALL;
++		s->setup_len = 0;
++		s->setup_state = SETUP_STATE_ACK;
+         return;
+     }
+ 
+@@ -277,6 +279,8 @@ static void do_parameter(USBDevice *s, USBPacket *p)
+                 "usb_generic_handle_packet: ctrl buffer too small (%d > %zu)\n",
+                 s->setup_len, sizeof(s->data_buf));
+         p->status = USB_RET_STALL;
++		s->setup_len = 0;
++		s->setup_state = SETUP_STATE_ACK;
+         return;
+     }
+ 
+-- 
+2.23.0
+