linux-kernel - Re: [PATCH v2] ext4: fix NULL pointer dereference from orig_data in fill

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Message-ID: <CAKYAXd_u813Q0k1iMMnfwORxXYDEBtpaKMig1FGBOKpNW3s3rg@mail.gmail.com>
Date:	Tue, 8 Nov 2011 08:06:43 +0900
From:	NamJae Jeon <linkinjeon@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Namjae Jeon <linkinjeon@...il.com>, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] ext4: fix NULL pointer dereference from orig_data in
 fill_super and remount.

2011/11/8 Ted Ts'o <tytso@....edu>:
> On Mon, Nov 07, 2011 at 11:01:51PM +0900, Namjae Jeon wrote:
>> Fix NULL pointer dereference from orig_data in fill_super and remount.
>>
>> Signed-off-by: Namjae Jeon <linkinjeon@...il.com>
>
> Um, did you even try to test this patch before submitting it?
>
> #1:   kstrdup() return NULL if data is NULL
>
> #2:  The kernel's printk and sprintf functions will translate
>     sprintf(buf, "%s", NULL) by filling in the string "NULL"
>
> #3:  The only use of orig_data is a cosmetic one, of printing out
>     the mount options which are passed in.
>
> #4:  If the user doesn't specify any mount options, data is NULL, and
>     your patch would cause those mounts to fail with ENOMEM.
>
> In summary, there is no problem here; a pendant might complain that
> it's possible for data to be non-NULL, and for orig_data to be null of
> the kstrdup failed, but in that case, other memory allocations done
> later in ext4_fill_super() will almost have certainly failed, so in
> practice won't get as far as the printk.
Hi. Ted.
Sorry, I will make a patch next time after testing. Thanks for your review.
And I checked how to handle this case in other filesystem.

btrfs try to handle like this.
------------------------------------------------------------------------------
	if (!options)
		goto out;

	/*
	 * strsep changes the string, duplicate it because parse_options
	 * gets called twice
	 */
	opts = kstrdup(options, GFP_KERNEL);
	if (!opts)
		return -ENOMEM;
-------------------------------------------------------------------------------

So I suggest that ext4 try to handle like this.
-------------------------------------------------------------------------------
        if(data) {
                orig_data = kstrdup(data, GFP_KERNEL);
                if(!orig_data)
                        return ret;
        }
-------------------------------------------------------------------------------
I want to know your opinion.
Thanks.
>
>                                        - Ted
>
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