Re: [PATCH v1 1/2] nfs_common: Do not encode an ACL with fewer than three entries

["Anna Schumaker" <anna@kernel.org>]

On Thu, Sep 24, 2026, at 5:22 PM, Chuck Lever wrote:
> nfsacl_encode() reports at least four wire entries for any ACL
> that has entries, because a three-entry ACL is sent as four with a
> synthesized ACL_MASK. The entry encoder then walks a_entries[] up
> to that count.
>
> A one- or two-entry ACL cannot arrive from setfacl, because
> set_posix_acl() validates it first. It can arrive from an NFS
> server. The NFS client caches a GETACL result without validating
> it, and posix_acl_create() hands the cached default ACL to
> nfs3_proc_setacls() when the client creates a directory. The walk
> then reads past the end of the posix_acl allocation and copies the
> bytes into the SETACL arguments.
>
> Report zero wire entries for an ACL with fewer than three, the
> same as for an ACL with none. Count them the same way in
> nfsacl_size(), which otherwise sizes such an ACL at four entries
> and leaves the reserved bytes unwritten in the SETACL arguments.
>
> Fixes: a257cdd0e217 ("[PATCH] NFSD: Add server support for NFSv3 ACLs.")
> Signed-off-by: Chuck Lever <cel@kernel.org>

Acked-by: Anna Schumaker <anna.schumaker@hammerspace.com>


> ---
>  fs/nfs_common/nfsacl.c | 3 ++-
>  include/linux/nfsacl.h | 5 +++--
>  2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c
> index e2eaac14fd8e..38bb2c294d7c 100644
> --- a/fs/nfs_common/nfsacl.c
> +++ b/fs/nfs_common/nfsacl.c
> @@ -93,7 +93,8 @@ xdr_nfsace_encode(struct xdr_array2_desc *desc, void *elem)
>  int nfsacl_encode(struct xdr_buf *buf, unsigned int base, struct inode *inode,
>  		  struct posix_acl *acl, int encode_entries, int typeflag)
>  {
> -	int entries = (acl && acl->a_count) ? max_t(int, acl->a_count, 4) : 0;
> +	int entries = (acl && acl->a_count >= 3) ?
> +		      max_t(int, acl->a_count, 4) : 0;
>  	struct nfsacl_encode_desc nfsacl_desc = {
>  		.desc = {
>  			.elem_size = 12,
> diff --git a/include/linux/nfsacl.h b/include/linux/nfsacl.h
> index 8e76a79cdc6a..e4155e69c8dd 100644
> --- a/include/linux/nfsacl.h
> +++ b/include/linux/nfsacl.h
> @@ -26,8 +26,9 @@ static inline unsigned int
>  nfsacl_size(struct posix_acl *acl_access, struct posix_acl *acl_default)
>  {
>  	unsigned int w = 16;
> -	w += max(acl_access ? (int)acl_access->a_count : 3, 4) * 12;
> -	if (acl_default)
> +	if (acl_access && acl_access->a_count >= 3)
> +		w += max((int)acl_access->a_count, 4) * 12;
> +	if (acl_default && acl_default->a_count >= 3)
>  		w += max((int)acl_default->a_count, 4) * 12;
>  	return w;
>  }
> -- 
> 2.55.0