Re: [PATCH] f2fs: data: fix possible overflow in check_swap_activate()

[Chao Yu <chao@kernel.org>]

Hi Sergey,

Thanks for the patch.

On 2023/10/26 4:20, Sergey Shtylyov wrote:
> In check_swap_activate(), if the *while* loop exits early (0- or 1-page
> long swap file), an overflow happens while calculating the value of the
> span parameter as the lowest_pblock variable ends up being greater than
> the highest_pblock variable. Let's set *span to 0 in this case...

What do you think of returning -EINVAL for such case? I assume this is a
corner case.

> 
> Found by Linux Verification Center (linuxtesting.org) with the SVACE static
> analysis tool.
> 
> Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> ---
> This patch is against the 'master' branch of Jaegeuk Kim's F2FS repo...
> 
>   fs/f2fs/data.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 916e317ac925..342cb0d5056d 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -4047,7 +4047,10 @@ static int check_swap_activate(struct swap_info_struct *sis,
>   		cur_lblock += nr_pblocks;
>   	}
>   	ret = nr_extents;
> -	*span = 1 + highest_pblock - lowest_pblock;
> +	if (lowest_pblock <= highest_pblock)

if (unlikely(higest_pblock < lowest_pblock))
	return -EINVAL;

*span = 1 + highest_pblock - lowest_pblock;

Thanks,

> +		*span = 1 + highest_pblock - lowest_pblock;
> +	else
> +		*span = 0;
>   	if (cur_lblock == 0)
>   		cur_lblock = 1;	/* force Empty message */
>   	sis->max = cur_lblock;