From 6f05a277961dc801ba6de4f0f3bc22184ae80b0f Mon Sep 17 00:00:00 2001
From: Alec Brown <alec.r.brown@oracle.com>
Date: Mon, 22 May 2023 16:52:49 -0400
Subject: kern/efi/mm: Fix use-after-free in finish boot services

In grub-core/kern/efi/mm.c, grub_efi_finish_boot_services() has an instance
where the memory for the variable finish_mmap_buf is freed, but on the next
iteration of a while loop, grub_efi_get_memory_map() uses finish_mmap_buf. To
prevent this, we can set finish_mmap_buf to NULL after the free.

Reference:https://git.savannah.gnu.org/cgit/grub.git/commit?id=6f05a277961dc801ba6de4f0f3bc22184ae80b0f
Conflict:NA

Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/kern/efi/mm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/grub-core/kern/efi/mm.c b/grub-core/kern/efi/mm.c
index 2be0e69..6a6fba8 100644
--- a/grub-core/kern/efi/mm.c
+++ b/grub-core/kern/efi/mm.c
@@ -263,6 +263,7 @@ grub_efi_finish_boot_services (grub_efi_uintn_t *outbuf_size, void *outbuf,
 				   &finish_desc_size, &finish_desc_version) <= 0)
 	{
 	  grub_free (finish_mmap_buf);
+	  finish_mmap_buf = NULL;
 	  return grub_error (GRUB_ERR_IO, "couldn't retrieve memory map");
 	}
 
@@ -274,10 +275,12 @@ grub_efi_finish_boot_services (grub_efi_uintn_t *outbuf_size, void *outbuf,
       if (status != GRUB_EFI_INVALID_PARAMETER)
 	{
 	  grub_free (finish_mmap_buf);
+	  finish_mmap_buf = NULL;
 	  return grub_error (GRUB_ERR_IO, "couldn't terminate EFI services");
 	}
 
       grub_free (finish_mmap_buf);
+      finish_mmap_buf = NULL;
       grub_printf ("Trying to terminate EFI services again\n");
     }
   grub_efi_is_finished = 1;
-- 
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