From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Maxim Suhanov <dfirblog@gmail.com>
Date: Tue, 3 Oct 2023 19:12:27 +0200
Subject: [PATCH] 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.

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 74515114287f..32ba8276dd8d 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: