[PATCH] nfs: use vfs setgid helper

[Christian Brauner <brauner@kernel.org>]

We've aligned setgid behavior over multiple kernel releases. The details
can be found in the following two merge messages:
cf619f891971 ("Merge tag 'fs.ovl.setgid.v6.2')
426b4ca2d6a5 ("Merge tag 'fs.setgid.v6.0')
Consistent setgid stripping behavior is now encapsulated in the
setattr_should_drop_sgid() helper which is used by all filesystems that
strip setgid bits outside of vfs proper. Switch nfs to rely on this
helper as well. Without this patch the setgid stripping tests in
xfstests will fail.

Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
 fs/nfs/inode.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 222a28320e1c..5001086500b3 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -42,6 +42,7 @@
 #include <linux/uaccess.h>
 #include <linux/iversion.h>
 
+#include "../internal.h"
 #include "nfs4_fs.h"
 #include "callback.h"
 #include "delegation.h"
@@ -717,9 +718,7 @@ void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr,
 		if ((attr->ia_valid & ATTR_KILL_SUID) != 0 &&
 		    inode->i_mode & S_ISUID)
 			inode->i_mode &= ~S_ISUID;
-		if ((attr->ia_valid & ATTR_KILL_SGID) != 0 &&
-		    (inode->i_mode & (S_ISGID | S_IXGRP)) ==
-		     (S_ISGID | S_IXGRP))
+		if (setattr_should_drop_sgid(&nop_mnt_idmap, inode))
 			inode->i_mode &= ~S_ISGID;
 		if ((attr->ia_valid & ATTR_MODE) != 0) {
 			int mode = attr->ia_mode & S_IALLUGO;

---
base-commit: eeac8ede17557680855031c6f305ece2378af326
change-id: 20230313-fs-nfs-setgid-659410a10b25