From: Patrick Ho <Patrick.Ho@netapp.com>
Date: Sat, 21 Aug 2021 02:56:26 -0400
Subject: [PATCH] nfsd: fix error handling of register_pernet_subsys() in
 init_nfsd()
Git-commit: 1d625050c7c2dd877e108e382b8aaf1ae3cfe1f4
Patch-mainline: v5.15-rc5
References: git-fixes

init_nfsd() should not unregister pernet subsys if the register fails
but should instead unwind from the last successful operation which is
register_filesystem().

Unregistering a failed register_pernet_subsys() call can result in
a kernel GPF as revealed by programmatically injecting an error in
register_pernet_subsys().

Verified the fix handled failure gracefully with no lingering nfsd
entry in /proc/filesystems.  This change was introduced by the commit
bd5ae9288d64 ("nfsd: register pernet ops last, unregister first"),
the original error handling logic was correct.

Fixes: bd5ae9288d64 ("nfsd: register pernet ops last, unregister first")
Cc: stable@vger.kernel.org
Signed-off-by: Patrick Ho <Patrick.Ho@netapp.com>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: NeilBrown <neilb@suse.de>

---
 fs/nfsd/nfsctl.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1549,7 +1549,7 @@ static int __init init_nfsd(void)
 		goto out_free_all;
 	return 0;
 out_free_all:
-	unregister_pernet_subsys(&nfsd_net_ops);
+	unregister_filesystem(&nfsd_fs_type);
 out_free_exports:
 	remove_proc_entry("fs/nfs/exports", NULL);
 	remove_proc_entry("fs/nfs", NULL);