File CVE-2016-1714-qemut-fw_cfg-add-check-to-validate-current-entry-value.patch of Package xen.openSUSE_Leap_42.3_Update

Reference: bsc#961692 CVE-2016-1714

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.

Reported-by: Donghai Zdh <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
---
 hw/nvram/fw_cfg.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Updated as per review in
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg00398.html

Index: xen-4.6.0-testing/tools/qemu-xen-traditional-dir-remote/hw/fw_cfg.c
===================================================================
--- xen-4.6.0-testing.orig/tools/qemu-xen-traditional-dir-remote/hw/fw_cfg.c
+++ xen-4.6.0-testing/tools/qemu-xen-traditional-dir-remote/hw/fw_cfg.c
@@ -54,11 +54,15 @@ typedef struct _FWCfgState {
 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];
 
     FW_CFG_DPRINTF("write %d\n", value);
 
-    if (s->cur_entry & FW_CFG_WRITE_CHANNEL && 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);
@@ -88,7 +92,8 @@ static int fw_cfg_select(FWCfgState *s,
 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)