From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Chris Coulson <chris.coulson@canonical.com>

Date: Wed, 22 Jul 2020 17:06:04 +0100

Subject: [PATCH] Fix a regression caused by "efi: fix some malformed device

 path arithmetic errors"

This commit introduced a bogus check inside copy_file_path to

determine whether the destination grub_efi_file_path_device_path_t

was valid before anything was copied to it. Depending on the

contents of the heap buffer, this check could fail which would

result in copy_file_path returning early.

Without any error propagated to the caller, make_file_path would

then try to advance the invalid device path node with

GRUB_EFI_NEXT_DEVICE_PATH, which would also fail, returning a NULL

pointer that would subsequently be dereferenced.

Remove the bogus check, and also propagate errors from copy_file_path.

---

 grub-core/loader/efi/chainloader.c | 26 ++++++++++++++------------

 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c

index b90dfd6c5a6..dbcdf333b62 100644

--- a/grub-core/loader/efi/chainloader.c

+++ b/grub-core/loader/efi/chainloader.c

@@ -115,7 +115,7 @@ grub_chainloader_boot (void)

   return grub_errno;

 }

-static void

+static grub_err_t

 copy_file_path (grub_efi_file_path_device_path_t *fp,

 		const char *str, grub_efi_uint16_t len)

 {

@@ -125,15 +125,9 @@ copy_file_path (grub_efi_file_path_device_path_t *fp,

   fp->header.type = GRUB_EFI_MEDIA_DEVICE_PATH_TYPE;

   fp->header.subtype = GRUB_EFI_FILE_PATH_DEVICE_PATH_SUBTYPE;

-  if (!GRUB_EFI_DEVICE_PATH_VALID ((grub_efi_device_path_t *)fp))

-    {

-      grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI Device Path is invalid");

-      return;

-    }

-

   path_name = grub_calloc (len, GRUB_MAX_UTF16_PER_UTF8 * sizeof (*path_name));

   if (!path_name)

-    return;

+    return grub_error (GRUB_ERR_OUT_OF_MEMORY, "failed to allocate path buffer");

   size = grub_utf8_to_utf16 (path_name, len * GRUB_MAX_UTF16_PER_UTF8,

 			     (const grub_uint8_t *) str, len, 0);

@@ -145,6 +139,8 @@ copy_file_path (grub_efi_file_path_device_path_t *fp,

   /* File Path is NULL terminated */

   fp->path_name[size++] = '\0';

   fp->header.length = size * sizeof (grub_efi_char16_t) + sizeof (*fp);

+  grub_free (path_name);

+  return GRUB_ERR_NONE;

 }

 static grub_efi_device_path_t *

@@ -202,13 +198,19 @@ make_file_path (grub_efi_device_path_t *dp, const char *filename)

   /* Fill the file path for the directory.  */

   d = (grub_efi_device_path_t *) ((char *) file_path

 				  + ((char *) d - (char *) dp));

-  copy_file_path ((grub_efi_file_path_device_path_t *) d,

-		  dir_start, dir_end - dir_start);

+  if (copy_file_path ((grub_efi_file_path_device_path_t *) d,

+		      dir_start, dir_end - dir_start) != GRUB_ERR_NONE)

+    {

+    fail:

+      grub_free (file_path);

+      return 0;

+    }

   /* Fill the file path for the file.  */

   d = GRUB_EFI_NEXT_DEVICE_PATH (d);

-  copy_file_path ((grub_efi_file_path_device_path_t *) d,

-		  dir_end + 1, grub_strlen (dir_end + 1));

+  if (copy_file_path ((grub_efi_file_path_device_path_t *) d,

+		      dir_end + 1, grub_strlen (dir_end + 1)) != GRUB_ERR_NONE)

+    goto fail;

   /* Fill the end of device path nodes.  */

   d = GRUB_EFI_NEXT_DEVICE_PATH (d);