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Subject: Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in
 __get_metapage
To:     Dave Kleikamp <dave.kleikamp@oracle.com>,
        jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org
References: <20171004082441.2405-1-juerg.haefliger@canonical.com>
 <1dbf4a54-968f-0ca7-da96-e262c653fecb@canonical.com>
 <c3ce64a1-65dc-0ed1-52ec-8bf950b77fb2@oracle.com>
 <778bc3d1-4bf4-ed83-3cc3-19d6efb5cceb@canonical.com>
 <0c8c1f0e-c3af-308f-aee0-d7b8c14f45d8@oracle.com>
From:   Juerg Haefliger <juerg.haefliger@canonical.com>
Message-ID: <50f61041-7507-6410-ddf5-36892759be8b@canonical.com>
Date:   Thu, 2 Nov 2017 14:43:42 +0100
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From: Juerg Haefliger <juerg.haefliger@canonical.com>
To: Dave Kleikamp <dave.kleikamp@oracle.com>,
 jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org
Message-ID: <50f61041-7507-6410-ddf5-36892759be8b@canonical.com>
Subject: Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in
 __get_metapage
References: <20171004082441.2405-1-juerg.haefliger@canonical.com>
 <1dbf4a54-968f-0ca7-da96-e262c653fecb@canonical.com>
 <c3ce64a1-65dc-0ed1-52ec-8bf950b77fb2@oracle.com>
 <778bc3d1-4bf4-ed83-3cc3-19d6efb5cceb@canonical.com>
 <0c8c1f0e-c3af-308f-aee0-d7b8c14f45d8@oracle.com>
In-Reply-To: <0c8c1f0e-c3af-308f-aee0-d7b8c14f45d8@oracle.com>

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On 11/02/2017 02:15 PM, Dave Kleikamp wrote:
> On 11/02/2017 01:59 AM, Juerg Haefliger wrote:
>>
>>
>> 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 *ino=
de,
>>> unsigned long lblock,
>>>  	} else {
>>>  		INCREMENT(mpStat.pagealloc);
>>>  		mp =3D alloc_metapage(GFP_NOFS);
>>> +		if (!mp)
>>> +			goto unlock;
>>>  		mp->page =3D page;
>>>  		mp->sb =3D inode->i_sb;
>>>  		mp->flag =3D 0;
>>
>> I don't understand. This is part of the patch that I sent.
>=20
> Doh! How'd I miss that?

:-)


>>
>>
>>>
>>> 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 man=
y
>>> callers.
>>
>> I don't understand this either :-) Yes, the callers do check for a nul=
l
>> pointer but things blow up (in __get_metapage) before that check witho=
ut
>> the above fix.
>=20
> Yeah, the fix to __get_metapage() is necessary. I'm not convinced the
> first part of the patch, to alloc_metapage(), is necessary.

It's not. I just thought it'd be nice to get some sort of notification
in the log when the alloc fails. But if the callers log it then that's fi=
ne.

=2E..Juerg


>>
>> ...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 als=
o emit
>>>>> an error message if that happens.
>>>>>
>>>>> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.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 =3D mempool_alloc(metapage_mempool, gfp_mask)=
;
>>>>> =20
>>>>> -	if (mp) {
>>>>> -		mp->lid =3D 0;
>>>>> -		mp->lsn =3D 0;
>>>>> -		mp->data =3D NULL;
>>>>> -		mp->clsn =3D 0;
>>>>> -		mp->log =3D NULL;
>>>>> -		init_waitqueue_head(&mp->wait);
>>>>> +	if (!mp) {
>>>>> +		jfs_err("mempool_alloc failed!\n");
>>>>> +		return NULL;
>>>>>  	}
>>>>> +
>>>>> +	mp->lid =3D 0;
>>>>> +	mp->lsn =3D 0;
>>>>> +	mp->data =3D NULL;
>>>>> +	mp->clsn =3D 0;
>>>>> +	mp->log =3D NULL;
>>>>> +	init_waitqueue_head(&mp->wait);
>>>>> +
>>>>>  	return mp;
>>>>>  }
>>>>> =20
>>>>> @@ -663,6 +667,8 @@ struct metapage *__get_metapage(struct inode *i=
node, unsigned long lblock,
>>>>>  	} else {
>>>>>  		INCREMENT(mpStat.pagealloc);
>>>>>  		mp =3D alloc_metapage(GFP_NOFS);
>>>>> +		if (!mp)
>>>>> +			goto unlock;
>>>>>  		mp->page =3D page;
>>>>>  		mp->sb =3D inode->i_sb;
>>>>>  		mp->flag =3D 0;
>>>>>
>>


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