nfs_remount(): don't leak, don't ignore LSM options quietly

mainline inclusion
from mainline-v5.0-rc1
commit 6a0440e5
category: bugfix
bugzilla: NA
CVE: NA

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

* if mount(2) passes something like "context=foo" with MS_REMOUNT
in flags (/sbin/mount.nfs will _not_ do that - you need to issue
the syscall manually), you'll get leaked copies for LSM options.
The reason is that instead of nfs_{alloc,free}_parsed_mount_data()
nfs_remount() uses kzalloc/kfree, which lacks the needed cleanup.

* selinux options are not changed on remount (as for any other
fs), but in case of NFS the failure is quiet - they are not compared
to what we used to have, with complaint in case of attempted changes.
Trivially fixed by converting to use of security_sb_remount().

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflict:
	fs/nfs/super.c

Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>

fs/nfs/super.c

@@ -2272,7 +2272,7 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
 					   options->version <= 6))))
 		return 0;
 
-	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	data = nfs_alloc_parsed_mount_data();
 	if (data == NULL)
 		return -ENOMEM;
 
@@ -2312,7 +2312,7 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
 	/* compare new mount options with old ones */
 	error = nfs_compare_remount_data(nfss, data);
 out:
-	kfree(data);
+	nfs_free_parsed_mount_data(data);
 	return error;
 }
 EXPORT_SYMBOL_GPL(nfs_remount);