linux-kernel - Re: [PATCH] ntfs: change check order in ntfs_attr

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Date:   Fri, 26 Aug 2022 18:15:20 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Hawkins Jiawei <yin31149@...il.com>
Cc:     Anton Altaparmakov <anton@...era.com>, akpm@...ux-foundation.org,
        chenxiaosong2@...wei.com, linux-kernel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        syzbot+5f8dcabe4a3b2c51c607@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] ntfs: change check order in ntfs_attr_find

On Fri, Aug 26, 2022 at 08:32:57PM +0800, Hawkins Jiawei wrote:
> > syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> >
> > Looks like it is improper check order that causes this bug.
> 
> Sorry for wrong command.
> #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
> index 52615e6090e1..6480cd2d371d 100644
> --- a/fs/ntfs/attrib.c
> +++ b/fs/ntfs/attrib.c
> @@ -594,10 +594,11 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
>  	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
>  		u8 *mrec_end = (u8 *)ctx->mrec +
>  		               le32_to_cpu(ctx->mrec->bytes_allocated);
> +		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end)
> +			break;

This definitely seems like a bug.  But your code won't build.  Syzbot
must have -Werror turned off?

Btw, this was in the original code, but those casts are ugly.  Ideally
there would be some way to get rid of them.  But otherwise at least
put a space after the u8.  "(u8 *)a < (u8 *)ctx->mrec".

>  		u8 *name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
>  			       a->name_length * sizeof(ntfschar);
> -		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
> -		    name_end > mrec_end)
> +		if (name_end > mrec_end)
>  			break;

regards,
dan carpenter