From 4e1d08ad2465dcc2c79d3be9c92ec166d8420a98 Mon Sep 17 00:00:00 2001
From: Maxim Suhanov <dfirblog@gmail.com>
Date: Mon, 28 Aug 2023 16:38:19 +0300
Subject: [PATCH 5/6] fs/ntfs: Fix an OOB read when parsing a volume label

This fix introduces checks to ensure that an NTFS volume label is always
read from the corresponding file record segment.

The current NTFS code allows the volume label string to be read from an
arbitrary, attacker-chosen memory location. However, the bytes read are
always treated as UTF-16LE. So, the final string displayed is mostly
unreadable and it can't be easily converted back to raw bytes.

The lack of this check is a minor issue, likely not causing a significant
data leak.

Reference:https://git.savannah.gnu.org/cgit/grub.git/commit/?id=1fe82c41e070385e273d7bb1cfb482627a3c28e8
Conflict:NA

Reported-by: Maxim Suhanov <dfirblog@gmail.com>
Signed-off-by: Maxim Suhanov <dfirblog@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/fs/ntfs.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index 2404566..e26dd59 100644
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -1209,13 +1209,29 @@ grub_ntfs_label (grub_device_t device, char **label)
 
   init_attr (&mft->attr, mft);
   pa = find_attr (&mft->attr, GRUB_NTFS_AT_VOLUME_NAME);
+
+  if (pa >= mft->buf + (mft->data->mft_size << GRUB_NTFS_BLK_SHR))
+    {
+      grub_error (GRUB_ERR_BAD_FS, "can\'t parse volume label");
+      goto fail;
+    }
+
+  if (mft->buf + (mft->data->mft_size << GRUB_NTFS_BLK_SHR) - pa < 0x16)
+    {
+      grub_error (GRUB_ERR_BAD_FS, "can\'t parse volume label");
+      goto fail;
+    }
+
   if ((pa) && (pa[8] == 0) && (u32at (pa, 0x10)))
     {
       int len;
 
       len = u32at (pa, 0x10) / 2;
       pa += u16at (pa, 0x14);
-      *label = get_utf8 (pa, len);
+      if (mft->buf + (mft->data->mft_size << GRUB_NTFS_BLK_SHR) - pa >= 2 * len)
+        *label = get_utf8 (pa, len);
+      else
+        grub_error (GRUB_ERR_BAD_FS, "can\'t parse volume label");
     }
 
 fail:
-- 
2.19.1