linux-kernel - [PATCH] ntfs: Fix validity check for file name attribute

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Date:   Mon, 14 Jun 2021 13:05:40 +0800
From:   Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To:     anton@...era.com
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
        linux-ntfs-dev@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org, gregkh@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+213ac8bb98f7f4420840@...kaller.appspotmail.com
Subject: [PATCH] ntfs: Fix validity check for file name attribute

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@...kaller.appspotmail.com
Tested-by: syzbot+213ac8bb98f7f4420840@...kaller.appspotmail.com
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.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