Re: [PATCH] block: fix "check bi_size overflow before merge"

[Ming Lei]

On Mon, Dec 09, 2019 at 08:11:14PM +0100, Andreas Gruenbacher wrote:
> This partially reverts commit e3a5d8e386c3fb973fa75f2403622a8f3640ec06.
> 
> Commit e3a5d8e386c3 ("check bi_size overflow before merge") adds a bio_full
> check to __bio_try_merge_page.  This will cause __bio_try_merge_page to fail
> when the last bi_io_vec has been reached.  Instead, what we want here is only
> the bi_size overflow check.
> 
> Fixes: e3a5d8e386c3 ("block: check bi_size overflow before merge")
> Cc: stable@xxxxxxxxxxxxxxx # v5.4+
> Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> ---
>  block/bio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 9d54aa37ce6c..a5d75f6bf4c7 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -754,10 +754,12 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
>  	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>  		return false;
>  
> -	if (bio->bi_vcnt > 0 && !bio_full(bio, len)) {
> +	if (bio->bi_vcnt > 0) {
>  		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
>  
>  		if (page_is_mergeable(bv, page, len, off, same_page)) {
> +			if (bio->bi_iter.bi_size > UINT_MAX - len)
> +				return false;
>  			bv->bv_len += len;
>  			bio->bi_iter.bi_size += len;
>  			return true;

page merging doesn't consume new bvec, so this patch is correct:

Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks,
Ming