grub2/0198-grub-core-commands-acpi.c-grub_acpi_create_ebda-Don-.patch

From fa35f13018c92b66f4a68e1f32ede2b0327f993b Mon Sep 17 00:00:00 2001
From: Nickolai Zeldovich <nickolai@csail.mit.edu>
Date: Thu, 7 Mar 2013 08:52:29 +0100
Subject: [PATCH 198/482] 	* grub-core/commands/acpi.c
 (grub_acpi_create_ebda): Don't 	dereference null pointer. While the
 code is technically correct, gcc 	may eliminate a null check if pointer
 is already dereferenced.

---
 ChangeLog                 | 6 ++++++
 grub-core/commands/acpi.c | 7 ++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index ca3d603..5fb9b77 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2013-03-07  Nickolai Zeldovich <nickolai@csail.mit.edu>
 
+	* grub-core/commands/acpi.c (grub_acpi_create_ebda): Don't
+	dereference null pointer. While the code is technically correct, gcc
+	may eliminate a null check if pointer is already dereferenced.
+
+2013-03-07  Nickolai Zeldovich <nickolai@csail.mit.edu>
+
 	* grub-core/normal/crypto.c (read_crypto_list): Fix incorrect
 	OOM check.
 	* grub-core/normal/term.c (read_terminal_list): Likewise.
diff --git a/grub-core/commands/acpi.c b/grub-core/commands/acpi.c
index 891e392..8000873 100644
--- a/grub-core/commands/acpi.c
+++ b/grub-core/commands/acpi.c
@@ -171,7 +171,7 @@ grub_acpi_create_ebda (void)
   struct grub_acpi_create_ebda_ctx ctx = {
     .highestlow = 0
   };
-  int ebda_kb_len;
+  int ebda_kb_len = 0;
   int mmapregion = 0;
   grub_uint8_t *ebda, *v1inebda = 0, *v2inebda = 0;
   grub_uint8_t *targetebda, *target;
@@ -179,8 +179,9 @@ grub_acpi_create_ebda (void)
   struct grub_acpi_rsdp_v20 *v2;
 
   ebda = (grub_uint8_t *) (grub_addr_t) ((*((grub_uint16_t *)0x40e)) << 4);
-  ebda_kb_len = *(grub_uint16_t *) ebda;
-  if (! ebda || ebda_kb_len > 16)
+  if (ebda)
+    ebda_kb_len = *(grub_uint16_t *) ebda;
+  if (ebda_kb_len > 16)
     ebda_kb_len = 0;
   ctx.ebda_len = (ebda_kb_len + 1) << 10;
 
-- 
1.8.2.1