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

[Max Kellermann <max.kellermann@ionos.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.

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;
+		}
+
 		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;
-- 
2.39.2