fs: use consistent setgid checks in is_sxid()

stable inclusion
from stable-v5.10.176
commit 183ca919544c898dfbb40f6b26d33bfe8765a986
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I87BGI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=183ca919544c898dfbb40f6b26d33bfe8765a986



--------------------------------

commit 8d84e39d upstream.

Now that we made the VFS setgid checking consistent an inode can't be
marked security irrelevant even if the setgid bit is still set. Make
this function consistent with all other helpers.

Note that enforcing consistent setgid stripping checks for file
modification and mode- and ownership changes will cause the setgid bit
to be lost in more cases than useed to be the case. If an unprivileged
user wrote to a non-executable setgid file that they don't have
privilege over the setgid bit will be dropped. This will lead to
temporary failures in some xfstests until they have been updated.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>