[PATCH v3 4/4] nfs/super: check NFS_CAP_ACLS instead of the NFS version

[Max Kellermann <mk@cm4all.com>]

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.

Signed-off-by: Max Kellermann <mk@cm4all.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Cc: stable@vger.kernel.org
---
 fs/nfs/super.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index dada09b391c6..dab79193f641 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -977,11 +977,14 @@ static void nfs_fill_super(struct super_block *sb, struct nfs_fs_context *ctx)
 	if (ctx && ctx->bsize)
 		sb->s_blocksize = nfs_block_size(ctx->bsize, &sb->s_blocksize_bits);
 
-	if (server->nfs_client->rpc_ops->version != 2) {
+	if (NFS_SB(sb)->caps & NFS_CAP_ACLS) {
 		/* The VFS shouldn't apply the umask to mode bits. We will do
 		 * so ourselves when necessary.
 		 */
 		sb->s_flags |= SB_POSIXACL;
+	}
+
+	if (server->nfs_client->rpc_ops->version != 2) {
 		sb->s_time_gran = 1;
 		sb->s_export_op = &nfs_export_ops;
 	} else
-- 
2.20.1