From 0ed2458cc4eff6d9a9199527e2a0b6d445802f94 Mon Sep 17 00:00:00 2001
From: Maxim Suhanov <dfirblog@gmail.com>
Date: Mon, 28 Aug 2023 16:32:33 +0300
Subject: [PATCH 2/6] fs/ntfs: Fix an OOB read when reading data from the
 resident $DATA attribute

When reading a file containing resident data, i.e., the file data is stored in
the $DATA attribute within the NTFS file record, not in external clusters,
there are no checks that this resident data actually fits the corresponding
file record segment.

When parsing a specially-crafted file system image, the current NTFS code will
read the file data from an arbitrary, attacker-chosen memory offset and of
arbitrary, attacker-chosen length.

This allows an attacker to display arbitrary chunks of memory, which could
contain sensitive information like password hashes or even plain-text,
obfuscated passwords from BS EFI variables.

This fix implements a check to ensure that resident data is read from the
corresponding file record segment only.

Fixes: CVE-2023-4693

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 | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index c3c4db117bba..a68e173d8285 100644
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -401,7 +401,18 @@ read_data (struct grub_ntfs_attr *at, grub_uint8_t *pa, grub_uint8_t *dest,
     {
       if (ofs + len > u32at (pa, 0x10))
 	return grub_error (GRUB_ERR_BAD_FS, "read out of range");
-      grub_memcpy (dest, pa + u32at (pa, 0x14) + ofs, len);
+
+      if (u32at (pa, 0x10) > (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR))
+	return grub_error (GRUB_ERR_BAD_FS, "resident attribute too large");
+
+      if (pa >= at->mft->buf + (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR))
+	return grub_error (GRUB_ERR_BAD_FS, "resident attribute out of range");
+
+      if (u16at (pa, 0x14) + u32at (pa, 0x10) >
+	  (grub_addr_t) at->mft->buf + (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR) - (grub_addr_t) pa)
+	return grub_error (GRUB_ERR_BAD_FS, "resident attribute out of range");
+
+      grub_memcpy (dest, pa + u16at (pa, 0x14) + ofs, len);
       return 0;
     }
 
-- 
2.43.0