[SECURITY PATCH 20/28] relocator: Fix grub_relocator_alloc_chunk_align() top memory allocation

[Daniel Kiper]

From: Alexey Makhalov <amakhalov@vmware.com>

Current implementation of grub_relocator_alloc_chunk_align()
does not allow allocation of the top byte.

Assuming input args are:
  max_addr = 0xfffff000;
  size = 0x1000;

And this is valid. But following overflow protection will
unnecessarily move max_addr one byte down (to 0xffffefff):
  if (max_addr > ~size)
    max_addr = ~size;

~size + 1 will fix the situation. In addition, check size
for non zero to do not zero max_addr.

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/lib/relocator.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/grub-core/lib/relocator.c b/grub-core/lib/relocator.c
index 5847aac36..f2c1944c2 100644
--- a/grub-core/lib/relocator.c
+++ b/grub-core/lib/relocator.c
@@ -1386,8 +1386,8 @@ grub_relocator_alloc_chunk_align (struct grub_relocator 
*rel,
   };
   grub_addr_t min_addr2 = 0, max_addr2;
 
-  if (max_addr > ~size)
-    max_addr = ~size;
+  if (size && (max_addr > ~size))
+    max_addr = ~size + 1;
 
 #ifdef GRUB_MACHINE_PCBIOS
   if (min_addr < 0x1000)
-- 
2.11.0