linux-kernel - Re: [PATCH v3] f2fs: fix potential .flags overflow on 32bit architecture

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Date:   Mon, 23 Mar 2020 10:19:44 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Joe Perches <joe@...ches.com>, <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH v3] f2fs: fix potential .flags overflow on 32bit
 architecture

On 2020/3/23 10:00, Joe Perches wrote:
> On Mon, 2020-03-23 at 09:25 +0800, Chao Yu wrote:
>> f2fs_inode_info.flags is unsigned long variable, it has 32 bits
>> in 32bit architecture, since we introduced FI_MMAP_FILE flag
>> when we support data compression, we may access memory cross
>> the border of .flags field, corrupting .i_sem field, result in
>> below deadlock.
>>
>> To fix this issue, let's expand .flags as an array to grab enough
>> space to store new flags.
> []
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> []
>> @@ -2586,22 +2590,28 @@ static inline void __mark_inode_dirty_flag(struct inode *inode,
>>  	}
>>  }
>>  
>> +static inline void __set_inode_flag(struct inode *inode, int flag)
>> +{
>> +	test_and_set_bit(flag % BITS_PER_LONG,
>> +			&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> I believe this should just use
> 
> 	test_and_set_bit(flag, F2FS_I(inode)->flags);
> 
>>  static inline int is_inode_flag_set(struct inode *inode, int flag)
>>  {
>> -	return test_bit(flag, &F2FS_I(inode)->flags);
>> +	return test_bit(flag % BITS_PER_LONG,
>> +				&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> here too.
> 
> 	test_bit(flag, F2FS_I(inode)->flags);
> 
>>  static inline void clear_inode_flag(struct inode *inode, int flag)
>>  {
>> -	if (test_bit(flag, &F2FS_I(inode)->flags))
>> -		clear_bit(flag, &F2FS_I(inode)->flags);
>> +	test_and_clear_bit(flag % BITS_PER_LONG,
>> +				&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> and here.

My bad, Ondřej Jirman also reminded me this issue, will fix this soon.

Thanks,

> 
> I also don't know why these functions are used at all.
> 
> 
> .
>