linux-kernel - Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in __get

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Message-ID: <778bc3d1-4bf4-ed83-3cc3-19d6efb5cceb@canonical.com>
Date:   Thu, 2 Nov 2017 07:59:09 +0100
From:   Juerg Haefliger <juerg.haefliger@...onical.com>
To:     Dave Kleikamp <dave.kleikamp@...cle.com>,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in
 __get_metapage



On 10/30/2017 11:13 PM, Dave Kleikamp wrote:
> On 10/25/2017 02:50 AM, Juerg Haefliger wrote:
>> Is this a patch you might consider?
> 
> Sorry it's taken me so long to respond.
> 
> I don't think this is the right fix. A failed allocation will still
> result in a null pointer dereference by the caller, __get_metapage(). I
> think the check needs to be put there. Like this:
> 
> --- a/fs/jfs/jfs_metapage.c
> +++ b/fs/jfs/jfs_metapage.c
> @@ -663,6 +663,8 @@ struct metapage *__get_metapage(struct inode *inode,
> unsigned long lblock,
>  	} else {
>  		INCREMENT(mpStat.pagealloc);
>  		mp = alloc_metapage(GFP_NOFS);
> +		if (!mp)
> +			goto unlock;
>  		mp->page = page;
>  		mp->sb = inode->i_sb;
>  		mp->flag = 0;

I don't understand. This is part of the patch that I sent.


> 
> Furthermore, it looks like all the callers of __get_metapage() check for
> a null return, so I'm not sure we need to handle the error at this
> point. I might have to look a bit harder at that, since there are many
> callers.

I don't understand this either :-) Yes, the callers do check for a null
pointer but things blow up (in __get_metapage) before that check without
the above fix.

...Juerg


> 
> Thanks,
> Shaggy
> 
>>
>> Thanks
>> ...Juerg
>>
>>
>> On 10/04/2017 10:24 AM, Juerg Haefliger wrote:
>>> alloc_metapage can return a NULL pointer so check for that. And also emit
>>> an error message if that happens.
>>>
>>> Signed-off-by: Juerg Haefliger <juerg.haefliger@...onical.com>
>>> ---
>>>  fs/jfs/jfs_metapage.c | 20 +++++++++++++-------
>>>  1 file changed, 13 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
>>> index 1c4b9ad4d7ab..00f21af66872 100644
>>> --- a/fs/jfs/jfs_metapage.c
>>> +++ b/fs/jfs/jfs_metapage.c
>>> @@ -187,14 +187,18 @@ static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
>>>  {
>>>  	struct metapage *mp = mempool_alloc(metapage_mempool, gfp_mask);
>>>  
>>> -	if (mp) {
>>> -		mp->lid = 0;
>>> -		mp->lsn = 0;
>>> -		mp->data = NULL;
>>> -		mp->clsn = 0;
>>> -		mp->log = NULL;
>>> -		init_waitqueue_head(&mp->wait);
>>> +	if (!mp) {
>>> +		jfs_err("mempool_alloc failed!\n");
>>> +		return NULL;
>>>  	}
>>> +
>>> +	mp->lid = 0;
>>> +	mp->lsn = 0;
>>> +	mp->data = NULL;
>>> +	mp->clsn = 0;
>>> +	mp->log = NULL;
>>> +	init_waitqueue_head(&mp->wait);
>>> +
>>>  	return mp;
>>>  }
>>>  
>>> @@ -663,6 +667,8 @@ struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
>>>  	} else {
>>>  		INCREMENT(mpStat.pagealloc);
>>>  		mp = alloc_metapage(GFP_NOFS);
>>> +		if (!mp)
>>> +			goto unlock;
>>>  		mp->page = page;
>>>  		mp->sb = inode->i_sb;
>>>  		mp->flag = 0;
>>>



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