Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To:     anton@tuxera.com
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
        linux-ntfs-dev@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
Subject: [PATCH] ntfs: Fix validity check for file name attribute
Date:   Mon, 14 Jun 2021 13:05:40 +0800
Message-Id: <20210614050540.289494-1-desmondcheongzx@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When checking the file name attribute, we want to ensure that it fits
within the bounds of ATTR_RECORD. To do this, we should check
that (attr record + file name offset + file name length) < (attr
record + attr record length).

However, the original check did not include the file name offset in
the calculation. This means that corrupted on-disk metadata might not
caught by the incorrect file name check, and lead to an invalid memory
access.

An example can be seen in the crash report of a memory corruption
error found by Syzbot:
https://syzkaller.appspot.com/bug?id=a1a1e379b225812688566745c3e2f7242bffc246

Adding the file name offset to the validity check fixes this error and
passes the Syzbot reproducer test.

Reported-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
Tested-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
 fs/ntfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index f5c058b3192c..4474adb393ca 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -477,7 +477,7 @@ static int ntfs_is_extended_system_file(ntfs_attr_search_ctx *ctx)
 		}
 		file_name_attr = (FILE_NAME_ATTR*)((u8*)attr +
 				le16_to_cpu(attr->data.resident.value_offset));
-		p2 = (u8*)attr + le32_to_cpu(attr->data.resident.value_length);
+		p2 = (u8 *)file_name_attr + le32_to_cpu(attr->data.resident.value_length);
 		if (p2 < (u8*)attr || p2 > p)
 			goto err_corrupt_attr;
 		/* This attribute is ok, but is it in the $Extend directory? */
-- 
2.25.1