Re: [PATCH] nfs/super: check NFS_CAP_ACLS instead of the NFS version

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2023-09-19 at 10:18 +0200, Max Kellermann wrote:
> This sets SB_POSIXACL only if ACL support is really enabled, instead
> of always setting SB_POSIXACL if the NFS protocol version
> theoretically supports ACL.
> 
> The code comment says "We will [apply the umask] ourselves", but that
> happens in posix_acl_create() only if the kernel has POSIX ACL
> support.  Without it, posix_acl_create() is an empty dummy function.
> 
> So let's not pretend we will apply the umask if we can already know
> that we will never.
> 
> This fixes a problem where the umask is always ignored in the NFS
> client when compiled without CONFIG_FS_POSIX_ACL.  This is a 4 year
> old regression caused by commit 013cdf1088d723 which itself was not
> completely wrong, but failed to consider all the side effects by
> misdesigned VFS code.
> 

A little more than 4 years now!

> Reviewed-by: J. Bruce Fields <bfields@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
> ---
>  fs/nfs/super.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/super.c b/fs/nfs/super.c
> index 0d6473cb00cb..051986b422b0 100644
> --- a/fs/nfs/super.c
> +++ b/fs/nfs/super.c
> @@ -1064,14 +1064,19 @@ static void nfs_fill_super(struct super_block *sb, struct nfs_fs_context *ctx)
>  		 * The VFS shouldn't apply the umask to mode bits.
>  		 * We will do so ourselves when necessary.
>  		 */
> -		sb->s_flags |= SB_POSIXACL;
> +		if (NFS_SB(sb)->caps & NFS_CAP_ACLS) {
> +			sb->s_flags |= SB_POSIXACL;
> +		}
> +

nit: curly braces aren't needed here

>  		sb->s_time_gran = 1;
>  		sb->s_time_min = 0;
>  		sb->s_time_max = U32_MAX;
>  		sb->s_export_op = &nfs_export_ops;
>  		break;
>  	case 4:
> -		sb->s_flags |= SB_POSIXACL;
> +		if (NFS_SB(sb)->caps & NFS_CAP_ACLS) {
> +			sb->s_flags |= SB_POSIXACL;
> +		}
>  		sb->s_time_gran = 1;
>  		sb->s_time_min = S64_MIN;
>  		sb->s_time_max = S64_MAX;


(cc'ing Christian)

This patch may have a minor conflict with this patch:

https://lore.kernel.org/linux-nfs/20230911-acl-fix-v3-1-b25315333f6c@kernel.org/

...but it seems like the right thing to do if POSIX ACLs are compiled
out.

Reviewed-by: Jeff Layton <jlayton@kernel.org>