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List:       oss-security
Subject:    [oss-security] CVE-2020-14364 QEMU: usb: out-of-bounds r/w access issue while processing usb packets
From:       P J P <ppandit () redhat ! com>
Date:       2020-08-24 12:52:51
Message-ID: nycvar.YSQ.7.78.906.2008241819340.306228 () xnncv
[Download RAW message or body]

Hello,

An out-of-bounds read/write access issue was found in the USB emulator of the 
QEMU. It occurs while processing USB packets from a guest, when 
'USBDevice->setup_len' exceeds the USBDevice->data_buf[4096], in 
do_token_{in,out} routines.

A guest user may use this flaw to crash the QEMU process resulting in DoS OR 
potentially execute arbitrary code with the privileges of the QEMU process on 
the host.

* Attached herein is an upstream patch from Gerd Hoffmann(CC'd) to fix this
   issue.

* 'CVE-2020-14364' is assigned to this issue by Red Hat Inc.

* This issue was independently reported by Ziming Zhang, Gonglei Arei and
   Yanyu Zhang(CC'd).

   Gonglei and Yanyu mentioned that the issue was found by Xiao Wei(CC'd).


Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D
["0001-usb-fix-setup-len-init.patch" (text/plain)]

>From c5bd2924c6d6a5bcbffb8b5e7798a88970131c07 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 17 Aug 2020 08:34:22 +0200
Subject: [PATCH] usb: fix setup_len init (CVE-2020-14364)

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} functions specifically)
from working with invalid USBDevice->setup_len values and overrunning
the USBDevice->setup_buf[] buffer.

Fixes: CVE-2020-14364
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/usb/core.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/hw/usb/core.c b/hw/usb/core.c
index 5abd128b6bc5..5234dcc73fea 100644
--- a/hw/usb/core.c
+++ b/hw/usb/core.c
@@ -129,6 +129,7 @@ void usb_wakeup(USBEndpoint *ep, unsigned int stream)
 static void do_token_setup(USBDevice *s, USBPacket *p)
 {
     int request, value, index;
+    unsigned int setup_len;
 
     if (p->iov.size != 8) {
         p->status = USB_RET_STALL;
@@ -138,14 +139,15 @@ static void do_token_setup(USBDevice *s, USBPacket *p)
     usb_packet_copy(p, s->setup_buf, p->iov.size);
     s->setup_index = 0;
     p->actual_length = 0;
-    s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];
-    if (s->setup_len > sizeof(s->data_buf)) {
+    setup_len = (s->setup_buf[7] << 8) | s->setup_buf[6];
+    if (setup_len > sizeof(s->data_buf)) {
         fprintf(stderr,
                 "usb_generic_handle_packet: ctrl buffer too small (%d > %zu)\n",
-                s->setup_len, sizeof(s->data_buf));
+                setup_len, sizeof(s->data_buf));
         p->status = USB_RET_STALL;
         return;
     }
+    s->setup_len = setup_len;
 
     request = (s->setup_buf[0] << 8) | s->setup_buf[1];
     value   = (s->setup_buf[3] << 8) | s->setup_buf[2];
@@ -259,26 +261,28 @@ static void do_token_out(USBDevice *s, USBPacket *p)
 static void do_parameter(USBDevice *s, USBPacket *p)
 {
     int i, request, value, index;
+    unsigned int setup_len;
 
     for (i = 0; i < 8; i++) {
         s->setup_buf[i] = p->parameter >> (i*8);
     }
 
     s->setup_state = SETUP_STATE_PARAM;
-    s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];
     s->setup_index = 0;
 
     request = (s->setup_buf[0] << 8) | s->setup_buf[1];
     value   = (s->setup_buf[3] << 8) | s->setup_buf[2];
     index   = (s->setup_buf[5] << 8) | s->setup_buf[4];
 
-    if (s->setup_len > sizeof(s->data_buf)) {
+    setup_len = (s->setup_buf[7] << 8) | s->setup_buf[6];
+    if (setup_len > sizeof(s->data_buf)) {
         fprintf(stderr,
                 "usb_generic_handle_packet: ctrl buffer too small (%d > %zu)\n",
-                s->setup_len, sizeof(s->data_buf));
+                setup_len, sizeof(s->data_buf));
         p->status = USB_RET_STALL;
         return;
     }
+    s->setup_len = setup_len;
 
     if (p->pid == USB_TOKEN_OUT) {
         usb_packet_copy(p, s->data_buf, s->setup_len);
-- 
2.18.4


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