Re: [RFC v2 12/14] xfs: make the calculation generic in xfs_sb_validate_fsb_count()

Darrick J. Wong
2024-02-13T16:26:12Z

On Tue, Feb 13, 2024 at 10:37:11AM +0100, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
>
> Instead of assuming that PAGE_SHIFT is always higher than the blocklog,
> make the calculation generic so that page cache count can be calculated
> correctly for LBS.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
> fs/xfs/xfs_mount.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index aabb25dc3efa..bfbaaecaf668 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -133,9 +133,13 @@ xfs_sb_validate_fsb_count(
> {
> ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
> ASSERT(sbp->sb_blocklog >= BBSHIFT);
> + unsigned long mapping_count;

Nit: indenting

unsigned long mapping_count;

> + uint64_t bytes = nblocks << sbp->sb_blocklog;

What happens if someone feeds us a garbage fs with sb_blocklog > 64?
Or did we check that previously, so an overflow isn't possible?

> +
> + mapping_count = bytes >> PAGE_SHIFT;

Does this result in truncation when unsigned long is 32 bits?

--D

>
> /* Limited by ULONG_MAX of page cache index */
> - if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
> + if (mapping_count > ULONG_MAX)
> return -EFBIG;
> return 0;
> }
> --
> 2.43.0
>
>