nfsd: new Kconfig option for legacy client tracking

We've had a number of attempts at different NFSv4 client tracking
methods over the years, but now nfsdcld has emerged as the clear winner
since the others (recoverydir and the usermodehelper upcall) are
problematic.

As a case in point, the recoverydir backend uses MD5 hashes to encode
long form clientid strings, which means that nfsd repeatedly gets dinged
on FIPS audits, since MD5 isn't considered secure. Its use of MD5 is not
cryptographically significant, so there is no danger there, but allowing
us to compile that out allows us to sidestep the issue entirely.

As a prelude to eventually removing support for these client tracking
methods, add a new Kconfig option that enables them. Mark it deprecated
and make it default to N.

Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/fs/nfsd/Kconfig b/fs/nfsd/Kconfig
index 43b88eaf0673..272ab8d5c4d7 100644
--- a/fs/nfsd/Kconfig
+++ b/fs/nfsd/Kconfig
@@ -158,3 +158,19 @@ config NFSD_V4_SECURITY_LABEL
 
 	If you do not wish to enable fine-grained security labels SELinux or
 	Smack policies on NFSv4 files, say N.
+
+config NFSD_LEGACY_CLIENT_TRACKING
+	bool "Support legacy NFSv4 client tracking methods (DEPRECATED)"
+	depends on NFSD_V4
+	default n
+	help
+	  The NFSv4 server needs to store a small amount of information on
+	  stable storage in order to handle state recovery after reboot. Most
+	  modern deployments upcall to a userland daemon for this (nfsdcld),
+	  but older NFS servers may store information directly in a
+	  recoverydir, or spawn a process directly using a usermodehelper
+	  upcall.
+
+	  These legacy client tracking methods have proven to be probelmatic
+	  and will be removed in the future. Say Y here if you need support
+	  for them in the interim.