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

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Date:	Thu, 09 Jun 2011 09:51:46 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
CC:	Shaohua Li <shaohua.li@...el.com>, linux-ext4@...r.kernel.org,
	"Ted Ts'o" <tytso@....edu>
Subject: Re: [patch]check NULL pointer

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().


> 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;
> 
> Again no data, no reason for backing off.

orig_data could be NULL if *data is NULL, or if kstrdup got ENOMEM.

Anyway, please describe how the bug can arise, and then we can better evaluate the change.

Thanks!

-Eric

>>  	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;
> 
> 
> This does not seem right, it there is no data we will end with ENOMEM
> for no reason.
> 
>>  	/* Store the original options */
>>  	lock_super(sb);
>>  	old_sb_flags = sb->s_flags;
>>
>>
>> --
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> 

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