Re: [PATCH 2/2] xfs: reserve quota for target dir expansion when renaming files

[Dave Chinner <david@fromorbit.com>]

On Thu, Mar 10, 2022 at 01:53:39PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> XFS does not reserve quota for directory expansion when renaming
> children into a directory.  This means that we don't reject the
> expansion with EDQUOT when we're at or near a hard limit, which means
> that unprivileged userspace can use rename() to exceed quota.
> 
> Rename operations don't always expand the target directory, and we allow
> a rename to proceed with no space reservation if we don't need to add a
> block to the target directory to handle the addition.  Moreover, the
> unlink operation on the source directory generally does not expand the
> directory (you'd have to free a block and then cause a btree split) and
> it's probably of little consequence to leave the corner case that
> renaming a file out of a directory can increase its size.
> 
> As with link and unlink, there is a further bug in that we do not
> trigger the blockgc workers to try to clear space when we're out of
> quota.
> 
> Because rename is its own special tricky animal, we'll patch xfs_rename
> directly to reserve quota to the rename transaction.  We'll leave
> cleaning up the rest of xfs_rename for the metadata directory tree
> patchset.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/xfs/xfs_inode.c |   33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)

LGTM.

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com