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

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Message-ID: <515c1447-9ca2-844c-0a89-a698157d14f6@huawei.com>
Date:   Fri, 12 Aug 2022 21:34:51 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Luís Henriques <lhenriques@...e.de>
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>, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v2] ext4: fix bug in extents parsing when eh_entries == 0
 and eh_depth > 0

Hi Luís,


On 8/12/2022 9:19 PM, Luís Henriques wrote:
> 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)))) {

le16_to_cpu(eh->eh_depth > 0) It's the wrong position of the parentheses here.

>> 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))) {
> 		/* ... */
> 	}

Yeah, but it could be more streamlined here.

The earlier judgment has guaranteed "depth == eh->eh_depth"

> And once again, thanks for your review!
>
> Cheers,

-- 
With Best Regards,
Baokun Li