Re: [PATCH] xfs: fix regression in "cleanup xfs_dir2_block_getdents"

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Mar 12, 2020 at 10:57:28AM +0200, Tommi Rantala wrote:
> Commit 263dde869bd09 ("xfs: cleanup xfs_dir2_block_getdents") introduced
> a getdents regression, when it converted the pointer arithmetics to
> offset calculations: offset is updated in the loop already for the next
> iteration, but the updated offset value is used incorrectly in two
> places, where we should have used the not-yet-updated value.
> 
> This caused for example "git clean -ffdx" failures to cleanup certain
> directory structures when running in a container.
> 
> Fix the regression by making sure we use proper offset in the loop body.
> Thanks to Christoph Hellwig for suggestion how to best fix the code.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Fixes: 263dde869bd09 ("xfs: cleanup xfs_dir2_block_getdents")
> Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>

Looks ok, sorry I didn't catch this either...
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

How might we package this up as a fstest so we can actually do
regression testing?

--D

> ---
>  fs/xfs/xfs_dir2_readdir.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
> index 0d3b640cf1cc..871ec22c9aee 100644
> --- a/fs/xfs/xfs_dir2_readdir.c
> +++ b/fs/xfs/xfs_dir2_readdir.c
> @@ -147,7 +147,7 @@ xfs_dir2_block_getdents(
>  	xfs_off_t		cook;
>  	struct xfs_da_geometry	*geo = args->geo;
>  	int			lock_mode;
> -	unsigned int		offset;
> +	unsigned int		offset, next_offset;
>  	unsigned int		end;
>  
>  	/*
> @@ -173,9 +173,10 @@ xfs_dir2_block_getdents(
>  	 * Loop over the data portion of the block.
>  	 * Each object is a real entry (dep) or an unused one (dup).
>  	 */
> -	offset = geo->data_entry_offset;
>  	end = xfs_dir3_data_end_offset(geo, bp->b_addr);
> -	while (offset < end) {
> +	for (offset = geo->data_entry_offset;
> +	     offset < end;
> +	     offset = next_offset) {
>  		struct xfs_dir2_data_unused	*dup = bp->b_addr + offset;
>  		struct xfs_dir2_data_entry	*dep = bp->b_addr + offset;
>  		uint8_t filetype;
> @@ -184,14 +185,15 @@ xfs_dir2_block_getdents(
>  		 * Unused, skip it.
>  		 */
>  		if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
> -			offset += be16_to_cpu(dup->length);
> +			next_offset = offset + be16_to_cpu(dup->length);
>  			continue;
>  		}
>  
>  		/*
>  		 * Bump pointer for the next iteration.
>  		 */
> -		offset += xfs_dir2_data_entsize(dp->i_mount, dep->namelen);
> +		next_offset = offset +
> +			xfs_dir2_data_entsize(dp->i_mount, dep->namelen);
>  
>  		/*
>  		 * The entry is before the desired starting point, skip it.
> -- 
> 2.21.1
>