linux-kernel - Re: [PATCH v2] fs/ntfs: fix BUG_ON of ntfs_read

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Date:   Fri, 24 Jun 2022 03:55:53 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Namjae Jeon <linkinjeon@...nel.org>
Cc:     Eric Biggers <ebiggers@...nel.org>, xu.xin16@....com.cn,
        anton@...era.com, linux-ntfs-dev@...ts.sourceforge.net,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Zeal Robot <zealci@....com.cn>,
        syzbot+6a5a7672f663cce8b156@...kaller.appspotmail.com,
        Songyi Zhang <zhang.songyi@....com.cn>,
        Yang Yang <yang.yang29@....com.cn>,
        Jiang Xuexin <jiang.xuexin@....com.cn>,
        Zhang wenya <zhang.wenya1@....com.cn>
Subject: Re: [PATCH v2] fs/ntfs: fix BUG_ON of ntfs_read_block()

On Fri, Jun 24, 2022 at 11:33:28AM +0900, Namjae Jeon wrote:
> 2022-06-24 2:08 GMT+09:00, Eric Biggers <ebiggers@...nel.org>:
> > On Thu, Jun 23, 2022 at 09:49:56AM +0000, cgel.zte@...il.com wrote:
> >> From: xu xin <xu.xin16@....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@...r.kernel.org
> >> Reported-by: Zeal Robot <zealci@....com.cn>
> >> Reported-by: syzbot+6a5a7672f663cce8b156@...kaller.appspotmail.com
> >> Reviewed-by: Songyi Zhang <zhang.songyi@....com.cn>
> >> Reviewed-by: Yang Yang <yang.yang29@....com.cn>
> >> Reviewed-by: Jiang Xuexin<jiang.xuexin@....com.cn>
> >> Reviewed-by: Zhang wenya<zhang.wenya1@....com.cn>
> >> Signed-off-by: xu xin <xu.xin16@....com.cn>
> >> ---
> >>
> >> Change for v2:
> >>  - Use ntfs_warning instead of WARN().
> >>  - Add the tag Cc: stable@...r.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?
> 
> ntfs_mapping_pairs_decompress() should return error pointer instead of NULL.
> Callers is checking error value using IS_ERR(). and the mapping pairs
> array of @MFT entry is empty, I think it's corrupted, it should cause
> mount failure.
> 
> I haven't checked if this patch fix the problem. Xu, Can you check it ?
> 

I have test it and it fixes the problem.

Thanks.

> diff --git a/fs/ntfs/runlist.c b/fs/ntfs/runlist.c
> index 97932fb5179c..31263fe0772f 100644
> --- a/fs/ntfs/runlist.c
> +++ b/fs/ntfs/runlist.c
> @@ -766,8 +766,11 @@ runlist_element
> *ntfs_mapping_pairs_decompress(const ntfs_volume *vol,
>                 return ERR_PTR(-EIO);
>         }
>         /* If the mapping pairs array is valid but empty, nothing to do. */
> -       if (!vcn && !*buf)
> +       if (!vcn && !*buf) {
> +               if (!old_rl)
> +                       return ERR_PTR(-EIO);
>                 return old_rl;
> +       }
>         /* Current position in runlist array. */
>         rlpos = 0;
>         /* Allocate first page and set current runlist size to one page. */
> 
> >
> > - Eric
> >