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From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Wed, 13 Dec 2017 13:38:37 +0100
Subject: [PATCH 06/41] fw_cfg: avoid calculating invalid current entry pointer
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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: <20171213133912.26176-7-marcandre.lureau@redhat.com>
Patchwork-id: 78355
O-Subject: [RHEL-7.5 qemu-kvm PATCH v3 06/41] fw_cfg: avoid calculating invalid current entry pointer
Bugzilla: 1411490
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

From: "Gabriel L. Somlo" <somlo@cmu.edu>

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>

(cherry picked from commit 66f8fd9dda312191b78d2a2ba2848bcee76127a2)

RHEL: fix minor conflicts due to previous partial backport in commit
      ba24567fd90702ea40ff320a79bc921b38510f22.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/nvram/fw_cfg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 85e950c..1317df7 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -301,7 +301,8 @@ static void fw_cfg_dma_transfer(FWCfgState *s)
     }
 
     arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
-    e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
+    e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
+        &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
 
     if (dma.control & FW_CFG_DMA_CTL_READ) {
         read = 1;
-- 
1.8.3.1