linux-kernel - Re: [PATCH v2] ext4: fix bug in extents parsing when eh_entries == 0 and eh

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Date:   Fri, 12 Aug 2022 14:19:47 +0100
From:   Luís Henriques <lhenriques@...e.de>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        wenqingliu0120@...il.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, "zhangyi (F)" <yi.zhang@...wei.com>,
        yebin10@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2] ext4: fix bug in extents parsing when eh_entries == 0
 and eh_depth > 0

Hi Baokun!

On Fri, Aug 12, 2022 at 08:50:34PM +0800, Baokun Li wrote:
> Hi Luís,
...
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 53cfe2c681c4..a5457ac1999c 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -460,6 +460,11 @@ static int __ext4_ext_check(const char *function, unsigned int line,
> >   		error_msg = "invalid eh_entries";
> >   		goto corrupted;
> >   	}
> > +	if (unlikely((le16_to_cpu(eh->eh_entries) == 0) &&
> > +		     (le16_to_cpu(eh->eh_depth > 0)))) {
> 
> The parentheses are misplaced,

I'm not sure I understand what you mean.  I want to have

	if (unlikely((CONDITION A) && (CONDITION B))) {
		/* ... */
	}

so they look correct.  Or is that a matter of style/alignment?  (Which
checkpatch.pl doesn't complains about, by the way.)

>and le16_to_cpu is not needed here.

OK, I guess that, since both conditions do a comparison against '0', the
le16_to_cpu() can be dropped.  And, if the parentheses problem you
mentioned above is a style problem, dropping it will also solve it because
that statement will become

	if (unlikely((eh->eh_entries == 0) && (eh->eh_depth > 0))) {
		/* ... */
	}

And once again, thanks for your review!

Cheers,
-- 
Luís

> 
> > +		error_msg = "eh_entries is 0 but eh_depth is > 0";
> > +		goto corrupted;
> > +	}
> >   	if (!ext4_valid_extent_entries(inode, eh, lblk, &pblk, depth)) {
> >   		error_msg = "invalid extent entries";
> >   		goto corrupted;
> > .
> 
> -- 
> With Best Regards,
> Baokun Li
>