[Xen-changelog] [qemu-xen stable-4.6] fw_cfg: add check to validate current entry value

[patchbot@xxxxxxx]

commit 18f2ce4bfe67f9b38143d9d96207e49c92b6881c
Author:     Prasad J Pandit <pjp@xxxxxxxxxxxxxxxxx>
AuthorDate: Wed Jan 6 11:46:25 2016 +0530
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CommitDate: Wed Jan 6 16:42:43 2016 +0000

    fw_cfg: add check to validate current entry value
    
    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 <donghai.zdh@xxxxxxxxxxxxxxx>
    Signed-off-by: Prasad J Pandit <pjp@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 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 a7122ee..cd3c6bf 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -211,12 +211,15 @@ 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);
@@ -245,7 +248,8 @@ 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)
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.6

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