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

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Date:   Sun, 22 Mar 2020 07:56:01 -0700
From:   Joe Perches <joe@...ches.com>
To:     Chao Yu <chao@...nel.org>, jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH v2] f2fs: fix potential .flags overflow on 32bit
 architecture

On Sun, 2020-03-22 at 21:56 +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> 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()