On Fri, Nov 10, 2023 at 6:06 AM Matthew Wilcox (Oracle) wrote:
>
> We must not shift by a negative number so work in terms of a byte
> offset to avoid the awkward shift left-or-right-depending-on-sign
> option. This means we need to use check_mul_overflow() to ensure
> that a large block number does not result in a wrap.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> fs/buffer.c | 17 ++++++-----------
> 1 file changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 44e0c0b7f71f..9c3f49cf8d28 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1085,26 +1085,21 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
> static bool grow_buffers(struct block_device *bdev, sector_t block,
> unsigned size, gfp_t gfp)
> {
> - pgoff_t index;
> - int sizebits;
> -
> - sizebits = PAGE_SHIFT - __ffs(size);
> - index = block >> sizebits;
> + loff_t pos;
>
> /*
> - * Check for a block which wants to lie outside our maximum possible
> - * pagecache index. (this comparison is done using sector_t types).
> + * Check for a block which lies outside our maximum possible
> + * pagecache index.
> */
> - if (unlikely(index != block >> sizebits)) {
> - printk(KERN_ERR "%s: requested out-of-range block %llu for "
> - "device %pg\n",
> + if (check_mul_overflow(block, size, &pos) || pos > MAX_LFS_FILESIZE) {
> + printk(KERN_ERR "%s: requested out-of-range block %llu for device %pg\n",
> __func__, (unsigned long long)block,
> bdev);
> return false;
> }
>
> /* Create a folio with the proper size buffers */
> - return grow_dev_folio(bdev, block, index, size, gfp);
> + return grow_dev_folio(bdev, block, pos / PAGE_SIZE, size, gfp);
"pos" has a loff_t type (= long long type).
Was it okay to do C division directly on 32-bit architectures?
Regards,
Ryusuke Konishi
> }
>
> static struct buffer_head *
> --
> 2.42.0
>
>
