From 04c86e0bb7b58fc2f913f798cdb18934933e532d Mon Sep 17 00:00:00 2001
From: Chris Coulson <chris.coulson@canonical.com>
Date: Fri, 29 Apr 2022 21:30:56 +0100
Subject: [PATCH] loader/efi/chainloader: Use grub_loader_set_ex

This ports the EFI chainloader to use grub_loader_set_ex() in order to fix
a use-after-free bug that occurs when grub_cmd_chainloader() is executed
more than once before a boot attempt is performed.

Fixes: CVE-2022-28736

Reference:https://src.fedoraproject.org/rpms/grub2/c/f0ad2aaa267a5d99b47f5c5770a55de0a702fdf0?branch=rawhide
Conflict:NA

Signed-off-by: Chris Coulson <chris.coulson@canonical.com>
(cherry picked from commit 4b7f0402b7cb0f67a93be736f2b75b818d7f44c9)
[rharwood: context sludge from other change]
Signed-off-by: Robbie Harwood <rharwood@redhat.com>
---
 grub-core/loader/efi/chainloader.c | 38 ++++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 16 deletions(-)
 
diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c
index 3342492ff1..fb874f1855 100644
--- a/grub-core/loader/efi/chainloader.c
+++ b/grub-core/loader/efi/chainloader.c
@@ -48,8 +48,6 @@ GRUB_MOD_LICENSE ("GPLv3+");
 
 static grub_dl_t my_mod;
 
-static grub_efi_handle_t image_handle;
-
 struct grub_secureboot_chainloader_context {
   grub_efi_physical_address_t address;
   grub_efi_uintn_t pages;
@@ -59,7 +57,6 @@ struct grub_secureboot_chainloader_context {
   grub_ssize_t cmdline_len;
   grub_efi_handle_t dev_handle;
 };
-static struct grub_secureboot_chainloader_context *sb_context;
 
 static grub_err_t
 grub_start_image (grub_efi_handle_t handle)
@@ -98,11 +95,14 @@ grub_start_image (grub_efi_handle_t handle)
 }
 
 static grub_err_t
-grub_chainloader_unload (void)
+grub_chainloader_unload (void *context)
 {
+  grub_efi_handle_t image_handle;
   grub_efi_loaded_image_t *loaded_image;
   grub_efi_boot_services_t *b;
 
+  image_handle = (grub_efi_handle_t) context;
+
   loaded_image = grub_efi_get_loaded_image (image_handle);
   if (loaded_image != NULL)
     grub_free (loaded_image->load_options);
@@ -115,10 +115,12 @@ grub_chainloader_unload (void)
 }
 
 static grub_err_t
-grub_chainloader_boot (void)
+grub_chainloader_boot (void *context)
 {
+  grub_efi_handle_t image_handle;
   grub_err_t err;
 
+  image_handle = (grub_efi_handle_t) context;
   err = grub_start_image (image_handle);
 
   grub_loader_unset ();
@@ -839,15 +841,17 @@ error_exit:
 }
 
 static grub_err_t
-grub_secureboot_chainloader_unload (void)
+grub_secureboot_chainloader_unload (void *context)
 {
+  struct grub_secureboot_chainloader_context *sb_context;
+
+  sb_context = (struct grub_secureboot_chainloader_context *) context;
+
   grub_efi_free_pages (sb_context->address, sb_context->pages);
   grub_free (sb_context->file_path);
   grub_free (sb_context->cmdline);
   grub_free (sb_context);
 
-  sb_context = 0;
-
   grub_dl_unref (my_mod);
   return GRUB_ERR_NONE;
 }
@@ -896,12 +900,15 @@ grub_load_image(grub_efi_device_path_t *file_path, void *boot_image,
 }
 
 static grub_err_t
-grub_secureboot_chainloader_boot (void)
+grub_secureboot_chainloader_boot (void *context)
 {
+  struct grub_secureboot_chainloader_context *sb_context;
   grub_efi_boot_services_t *b;
   int rc;
   grub_efi_handle_t handle = 0;
 
+  sb_context = (struct grub_secureboot_chainloader_context *) context;
+
   rc = handle_image (sb_context);
   if (rc == 0)
     {
@@ -942,6 +949,8 @@ grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)),
   grub_efi_char16_t *cmdline = 0;
   grub_ssize_t cmdline_len = 0;
   grub_efi_handle_t dev_handle = 0;
+  grub_efi_handle_t image_handle = 0;
+  struct grub_secureboot_chainloader_context *sb_context = 0;
 
   if (argc == 0)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
@@ -1127,8 +1136,8 @@ grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)),
       grub_file_close (file);
       grub_device_close (dev);
 
-      grub_loader_set (grub_secureboot_chainloader_boot,
-		       grub_secureboot_chainloader_unload, 0);
+      grub_loader_set_ex (grub_secureboot_chainloader_boot,
+			  grub_secureboot_chainloader_unload, sb_context, 0);
       return 0;
     }
   else
@@ -1142,7 +1151,7 @@ grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)),
       efi_call_2 (b->free_pages, address, pages);
       grub_free (file_path);
 
-      grub_loader_set (grub_chainloader_boot, grub_chainloader_unload, 0);
+      grub_loader_set_ex (grub_chainloader_boot, grub_chainloader_unload, image_handle, 0);
 
       return 0;
     }
@@ -1169,10 +1178,7 @@ fail:
     grub_free (cmdline);
 
   if (image_handle != 0)
-    {
-      efi_call_1 (b->unload_image, image_handle);
-      image_handle = 0;
-    }
+    efi_call_1 (b->unload_image, image_handle);
 
   grub_dl_unref (my_mod);
 
-- 
2.19.1