Re: [PATCH v2] fs/ntfs: fix BUG_ON of ntfs_read_block()

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Jun 23, 2022 at 09:49:56AM +0000, cgel.zte@gmail.com wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> As the bug description at
> https://lore.kernel.org/lkml/20220623033635.973929-1-xu.xin16@zte.com.cn/
> attckers can use this bug to crash the system.
> 
> So to avoid panic, remove the BUG_ON, and use ntfs_warning to output a
> warning to the syslog and return instead until someone really solve
> the problem.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Zeal Robot <zealci@zte.com.cn>
> Reported-by: syzbot+6a5a7672f663cce8b156@syzkaller.appspotmail.com
> Reviewed-by: Songyi Zhang <zhang.songyi@zte.com.cn>
> Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
> Reviewed-by: Jiang Xuexin<jiang.xuexin@zte.com.cn>
> Reviewed-by: Zhang wenya<zhang.wenya1@zte.com.cn>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---
> 
> Change for v2:
>  - Use ntfs_warning instead of WARN().
>  - Add the tag Cc: stable@vger.kernel.org.
> ---
>  fs/ntfs/aops.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
> index 5f4fb6ca6f2e..84d68efb4ace 100644
> --- a/fs/ntfs/aops.c
> +++ b/fs/ntfs/aops.c
> @@ -183,7 +183,12 @@ static int ntfs_read_block(struct page *page)
>  	vol = ni->vol;
>  
>  	/* $MFT/$DATA must have its complete runlist in memory at all times. */
> -	BUG_ON(!ni->runlist.rl && !ni->mft_no && !NInoAttr(ni));
> +	if (unlikely(!ni->runlist.rl && !ni->mft_no && !NInoAttr(ni))) {
> +		ntfs_warning(vi->i_sb, "Error because ni->runlist.rl, ni->mft_no, "
> +				"and NInoAttr(ni) is null.");
> +		unlock_page(page);
> +		return -EINVAL;
> +	}

A better warning message that doesn't rely on implementation details (struct
field and macro names) would be "Runlist of $MFT/$DATA is not cached".  Also,
why does this situation happen in the first place?  Is there a way to prevent
this situation in the first place?

- Eric