Re: [PATCH v2] f2fs: fix potential .flags overflow on 32bit architecture

[Chao Yu]

On 2020/3/22 22:56, Joe Perches wrote:
> On Sun, 2020-03-22 at 21:56 +0800, Chao Yu wrote:
>> From: Chao Yu <yuchao0@xxxxxxxxxx>
>>
>> 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.
> []
>> +static inline void __set_inode_flag(struct inode *inode, int flag)
>> +{
>> +	if (!test_bit(flag % BITS_PER_LONG,
>> +			&F2FS_I(inode)->flags[BIT_WORD(flag)]))
>> +		set_bit(flag % BITS_PER_LONG,
>> +			&F2FS_I(inode)->flags[BIT_WORD(flag)]);
>> +}
> 
> I believe you don't need to do anything like this
> but just let test_bit and set_bit do the indexing.
> 
> 	if (!test_bit(flg, F2FS_I(inode->flags)))
> 		set_bit(flag, F2FS_I(inode->flags));
> 
> And there already is a function called test_and_set_bit()

Yup, I've cleaned up with test_and_{set,clear}_bit(), thanks for your
reminder.

Thanks,

> 
> 
> .
>