From 5d12c17191e042a57e02749cedc55104a8251ac3 Mon Sep 17 00:00:00 2001
From: Miroslav Rezanina <mrezanin@redhat.com>
Date: Thu, 21 Jan 2016 07:17:43 +0100
Subject: [PATCH] fw_cfg: add check to validate current entry value
 (CVE-2016-1714)
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Message-id: <1453360663-5066-1-git-send-email-mrezanin@redhat.com>
Patchwork-id: 68834
O-Subject: [RHEL-7.2.z/RHEL-7.3 qemu-kvm PATCH] fw_cfg: add check to validate current entry value (CVE-2016-1714)
Bugzilla: 1298047
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Gerd Hoffmann <kraxel@redhat.com>

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

When processing firmware configurations, an OOB r/w access occurs
if 's->cur_entry' is set to be invalid(FW_CFG_INVALID=0xffff).
Add a check to validate 's->cur_entry' to avoid such access.

This patch is based on upstream commit 66f8fd9dda312191b78d2a2ba2848bcee76127a2
  Author: Gabriel L. Somlo <somlo@cmu.edu>
  Date:   Thu Nov 5 09:32:50 2015 -0500

    fw_cfg: avoid calculating invalid current entry pointer

    When calculating a pointer to the currently selected fw_cfg item, the
    following is used:

      FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];

    When s->cur_entry is FW_CFG_INVALID, we are calculating the address of
    a non-existent element in s->entries[arch][...], which is undefined.

    This patch ensures the resulting entry pointer is set to NULL whenever
    s->cur_entry is FW_CFG_INVALID.

    Reported-by: Laszlo Ersek <lersek@redhat.com>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
    Message-id: 1446733972-1602-5-git-send-email-somlo@cmu.edu
    Cc: Marc Marí <markmb@redhat.com>
    Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

with added chunk for fw_cfg_write() that was removed in commit
023e3148567ac898c7258138f8e86c3c2bb40d07
and missing chunk for fw_cfg_dma_transfer that was added in commit
a4c0d1deb785611c96a455f65ec032976b00b36f.

Reported-by: Donghai Zdh <donghai.zdh@alibaba-inc.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/nvram/fw_cfg.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index b865c09..fcb3146 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -207,12 +207,15 @@ static void fw_cfg_reboot(FWCfgState *s)
 static void fw_cfg_write(FWCfgState *s, uint8_t value)
 {
     int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
-    FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
+    FWCfgEntry *e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
+                     &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
 
     trace_fw_cfg_write(s, value);
 
-    if (s->cur_entry & FW_CFG_WRITE_CHANNEL && e->callback &&
-        s->cur_offset < e->len) {
+    if (s->cur_entry & FW_CFG_WRITE_CHANNEL
+        && e != NULL
+        && e->callback
+        && s->cur_offset < e->len) {
         e->data[s->cur_offset++] = value;
         if (s->cur_offset == e->len) {
             e->callback(e->callback_opaque, e->data);
@@ -241,7 +244,8 @@ static int fw_cfg_select(FWCfgState *s, uint16_t key)
 static uint8_t fw_cfg_read(FWCfgState *s)
 {
     int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
-    FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
+    FWCfgEntry *e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
+                     &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
     uint8_t ret;
 
     if (s->cur_entry == FW_CFG_INVALID || !e->data || s->cur_offset >= e->len)
-- 
1.8.3.1