linux-kernel - Re: [PATCH] f2fs: fix potential overflow in build_sit

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Date:   Wed, 9 Aug 2017 18:23:12 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH] f2fs: fix potential overflow in build_sit_info

Sorry, please ignore this patch. :(

Thanks,

On 2017/8/9 18:09, Chao Yu wrote:
> On a 32-bit system, below calculation may overflow the 32-bit unsigned
> integer, allocating a buffer size that smaller than needed. A write on
> the buffer will then trigger an out of boundary write.
> 1. MAIN_SEGS(sbi) * sizeof(struct seg_entry)
> 2. MAIN_SECS(sbi) * sizeof(struct sec_entry)
> 
> Fixes this by doing type cast before calculating.
> 
> This patch fixes CVE-2017-10662.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/segment.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 682ae68b9ef7..947674b5f466 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2997,8 +2997,9 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>  
>  	SM_I(sbi)->sit_info = sit_i;
>  
> -	sit_i->sentries = kvzalloc(MAIN_SEGS(sbi) *
> -					sizeof(struct seg_entry), GFP_KERNEL);
> +	sit_i->sentries = kvzalloc((unsigned long long)MAIN_SEGS(sbi) *
> +				(unsigned long long)sizeof(struct seg_entry),
> +				GFP_KERNEL);
>  	if (!sit_i->sentries)
>  		return -ENOMEM;
>  
> @@ -3036,8 +3037,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>  		return -ENOMEM;
>  
>  	if (sbi->segs_per_sec > 1) {
> -		sit_i->sec_entries = kvzalloc(MAIN_SECS(sbi) *
> -					sizeof(struct sec_entry), GFP_KERNEL);
> +		sit_i->sec_entries = kvzalloc(
> +				(unsigned long long)MAIN_SECS(sbi) *
> +				(unsigned long long)sizeof(struct sec_entry),
> +				GFP_KERNEL);
>  		if (!sit_i->sec_entries)
>  			return -ENOMEM;
>  	}
>