linux-ext4 - Re: [patch]check NULL pointer

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Date:	Fri, 10 Jun 2011 10:32:35 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Shaohua Li <shaohua.li@...el.com>
cc:	Eric Sandeen <sandeen@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Ted Ts'o" <tytso@....edu>
Subject: Re: [patch]check NULL pointer

On Fri, 10 Jun 2011, Shaohua Li wrote:

> On Thu, 2011-06-09 at 22:51 +0800, Eric Sandeen wrote:
> > On 6/9/11 4:24 AM, Lukas Czerner wrote:
> > > On Thu, 9 Jun 2011, Shaohua Li wrote:
> > > 
> > >> orig_data could be NULL.
> > > 
> > > Now, that is the commit description :). Could you please be more
> > > descriptive in the "descritpion" ? Also the subject is not right either,
> > > please see Documentation/SubmittingPatches
> > 
> > Yes; if possible please use the commit message to describe how/why orig_data
> > can be NULL; a testcase if one exists; the resulting flaw (null pointer deref?)
> > etc.
> > 
> > something like:
> > 
> > Subject: [PATCH] ext4: check for NULL orig_data pointer in mount paths
> > 
> > The orig_data pointer in ext4_fill_super()  and ext4_remount()
> > can be null if < ??? >, which can lead to < ??? > in the mount
> > and remount paths.  This can be demonstrated by < ??? >.  
> > To avoid this, we can simply test for the null pointer
> > and return an error in ext4_fill_super() and ext4_remount().
> I thought the reason is pretty straightforward, anyway here is the
> updated patch.
> 
> Subject: [patch]ext4: check NULL pointer for mount and remount
> 
> orig_data could be NULL, because the memory allocation of kstrdup() could fail.
> Add the NULL check.

I am sorry, but as I pointed out in previous mail this is not true.
*orig_data can be also NULL in the case that *data is NULL and hence
there is no reason for exiting with error. Also please use the subject
Eric suggested.

Thanks!
-Lukas

> 
> Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index cc5c157..45fc255 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3057,6 +3057,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  	unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
>  	ext4_group_t first_not_zeroed;
>  
> +	if (!orig_data)
> +		return ret;
>  	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>  	if (!sbi)
>  		goto out_free_orig;
> @@ -4285,6 +4287,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>  #endif
>  	char *orig_data = kstrdup(data, GFP_KERNEL);
>  
> +	if (!orig_data)
> +		return -ENOMEM;
>  	/* Store the original options */
>  	lock_super(sb);
>  	old_sb_flags = sb->s_flags;
> 
> 
> 

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