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Subject: Re: [PATCH] ntfs: Fix validity check for file name attribute
To:     anton@tuxera.com
Cc:     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
References: <20210614050540.289494-1-desmondcheongzx@gmail.com>
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Message-ID: <ea63e5af-6ac4-08fe-4261-904d55392b10@gmail.com>
Date:   Mon, 28 Jun 2021 10:45:51 +0800
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On 14/6/21 1:05 pm, Desmond Cheong Zhi Xi wrote:
> 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? */
> 

Hi Anton,

Any chance to review this patch?

Best wishes,
Desmond