Re: [PATCH 01/10] xfs: zero inode fork buffer at allocation

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, May 04, 2022 at 08:17:19AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> When we first allocate or resize an inline inode fork, we round up
> the allocation to 4 byte alingment to make journal alignment
> constraints. We don't clear the unused bytes, so we can copy up to
> three uninitialised bytes into the journal. Zero those bytes so we
> only ever copy zeros into the journal.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Yup.  Thanks for the cleanup.
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_inode_fork.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
> index 9aee4a1e2fe9..a15ff38c3d41 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.c
> +++ b/fs/xfs/libxfs/xfs_inode_fork.c
> @@ -50,8 +50,13 @@ xfs_init_local_fork(
>  		mem_size++;
>  
>  	if (size) {
> +		/*
> +		 * As we round up the allocation here, we need to ensure the
> +		 * bytes we don't copy data into are zeroed because the log
> +		 * vectors still copy them into the journal.
> +		 */
>  		real_size = roundup(mem_size, 4);
> -		ifp->if_u1.if_data = kmem_alloc(real_size, KM_NOFS);
> +		ifp->if_u1.if_data = kmem_zalloc(real_size, KM_NOFS);
>  		memcpy(ifp->if_u1.if_data, data, size);
>  		if (zero_terminate)
>  			ifp->if_u1.if_data[size] = '\0';
> @@ -500,10 +505,11 @@ xfs_idata_realloc(
>  	/*
>  	 * For inline data, the underlying buffer must be a multiple of 4 bytes
>  	 * in size so that it can be logged and stay on word boundaries.
> -	 * We enforce that here.
> +	 * We enforce that here, and use __GFP_ZERO to ensure that size
> +	 * extensions always zero the unused roundup area.
>  	 */
>  	ifp->if_u1.if_data = krealloc(ifp->if_u1.if_data, roundup(new_size, 4),
> -				      GFP_NOFS | __GFP_NOFAIL);
> +				      GFP_NOFS | __GFP_NOFAIL | __GFP_ZERO);
>  	ifp->if_bytes = new_size;
>  }
>  
> -- 
> 2.35.1
>