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Date:	Thu, 24 Jul 2014 14:14:36 +0400
From:	Andrey Tsyvarev <tsyvarev@...ras.ru>
To:	Gu Zheng <guz.fnst@...fujitsu.com>, Chao Yu <chao2.yu@...sung.com>
CC:	'Jaegeuk Kim' <jaegeuk@...nel.org>,
	'linux-kernel' <linux-kernel@...r.kernel.org>,
	'Alexey Khoroshilov' <khoroshilov@...ras.ru>,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] f2fs: Possible use-after-free when umount filesystem

Hi,

With patch skipping invalidating pages for node_inode and meta_inode 
use-after-free error disappears too.

23.07.2014 7:39, Gu Zheng пишет:
> Hi,
> On 07/23/2014 10:12 AM, Chao Yu wrote:
>
>> Hi Andrey Gu,
>>
>>> -----Original Message-----
>>> From: Andrey Tsyvarev [mailto:tsyvarev@...ras.ru]
>>> Sent: Tuesday, July 22, 2014 6:04 PM
>>> To: Gu Zheng
>>> Cc: Jaegeuk Kim; linux-kernel; Alexey Khoroshilov; linux-f2fs-devel@...ts.sourceforge.net
>>> Subject: Re: [f2fs-dev] f2fs: Possible use-after-free when umount filesystem
>>>
>>> Hi Gu,
>>>
>>>>> Investigation shows, that f2fs_evict_inode, when called for 'meta_inode', uses
>>> invalidate_mapping_pages() for 'node_inode'.
>>>>> But 'node_inode' is deleted before 'meta_inode' in f2fs_put_super via iput().
>>>>>
>>>>> It seems that in common usage scenario this use-after-free is benign, because 'node_inode'
>>> remains partially valid data even after kmem_cache_free().
>>>>> But things may change if, while 'meta_inode' is evicted in one f2fs filesystem, another (mounted)
>>> f2fs filesystem requests inode from cache, and formely
>>>>> 'node_inode' of the first filesystem is returned.
>>>> The analysis seems reasonable. Have you tried to swap the reclaim order of node_inde
>>>> and meta_inode?
>>>>
>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>> index 870fe19..e114418 100644
>>>> --- a/fs/f2fs/super.c
>>>> +++ b/fs/f2fs/super.c
>>>> @@ -430,8 +430,8 @@ static void f2fs_put_super(struct super_block *sb)
>>>>           if (sbi->s_dirty && get_pages(sbi, F2FS_DIRTY_NODES))
>>>>                   write_checkpoint(sbi, true);
>>>>
>>>> -       iput(sbi->node_inode);
>>>>           iput(sbi->meta_inode);
>>>> +       iput(sbi->node_inode);
>>>>
>>>>           /* destroy f2fs internal modules */
>>>>           destroy_node_manager(sbi);
>>>>
>>>> Thanks,
>>>> Gu
>>> With reclaim order of node_inode and meta_inode swapped, use-after-free
>>> error disappears.
>>>
>>> But shouldn't initialization order of these inodes be swapped too?
>>> As meta_inode uses node_inode, it seems logical that it should be
>>> initialized after it.
> The initialization order dose not affect anything, so swapping the order dose not
> make more sense here.
>
>> IMO, it's not easy to exchange order of initialization between meta_inode and
>> node_inode, because we should use meta_inode in get_valid_checkpoint for valid
>> cp first for usual verification, then init node_inode.
> Yeah, but I think just moving node_inode's initialization to the front of meta_inode
> dose not break anything.
>
>> As I checked, nids for both meta_inode and node_inode are reservation, so it's not
>> necessary for us to invalidate pages which will never alloced.
>>
>> How about skipping it as following?
> It seems the right way to fix this issue.
>
> To Andrey:
> Could you please try this one?
>
> Thanks,
> Gu
>
>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>> index 2cf6962..cafba3c 100644
>> --- a/fs/f2fs/inode.c
>> +++ b/fs/f2fs/inode.c
>> @@ -273,7 +273,7 @@ void f2fs_evict_inode(struct inode *inode)
>>   
>>   	if (inode->i_ino == F2FS_NODE_INO(sbi) ||
>>   			inode->i_ino == F2FS_META_INO(sbi))
>> -		goto no_delete;
>> +		goto out_clear;
>>   
>>   	f2fs_bug_on(get_dirty_dents(inode));
>>   	remove_dirty_dir_inode(inode);
>> @@ -295,6 +295,7 @@ void f2fs_evict_inode(struct inode *inode)
>>   
>>   	sb_end_intwrite(inode->i_sb);
>>   no_delete:
>> -	clear_inode(inode);
>>   	invalidate_mapping_pages(NODE_MAPPING(sbi), inode->i_ino, inode->i_ino);
>> +out_clear:
>> +	clear_inode(inode);
>>   }
>>
>>> --
>>> Best regards,
>>>
>>> Andrey Tsyvarev
>>> Linux Verification Center, ISPRAS
>>> web:http://linuxtesting.org
>>>
>>>
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>>> _______________________________________________
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>>> Linux-f2fs-devel@...ts.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>> .
>>
>
>

-- 
Best regards,

Andrey Tsyvarev
Linux Verification Center, ISPRAS
web:http://linuxtesting.org

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