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

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