[PATCH v1 03/36] NFS: Use nlmclnt_rpc_clnt() helper to retrieve nlm_host's rpc_clnt

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

The external API definitions for lockd reside in linux/lockd/bind.h.
Because "struct nlm_host" is an internal lockd structure, bind.h
does not include a definition of it. Dereferencing that structure
outside of lockd violates the layering boundary between NFS and
lockd.

The proper approach is to use the nlmclnt_rpc_clnt() helper function
already provided in lockd/bind.h, which retrieves the NLM host's
struct rpc_clnt without exposing internal lockd structures. This
maintains clean separation between the NFS client and lockd
internals.

Note that the nlm_host's h_rpcclnt field can be NULL during
initialization (host.c:141) or after cleanup (host.c:629). Add a
NULL check before calling shutdown_client() to prevent a potential
NULL pointer dereference in the sysfs shutdown path.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfs/sysfs.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
index ea6e6168092b..186b29de0129 100644
--- a/fs/nfs/sysfs.c
+++ b/fs/nfs/sysfs.c
@@ -12,7 +12,7 @@
 #include <linux/string.h>
 #include <linux/nfs_fs.h>
 #include <linux/rcupdate.h>
-#include <linux/lockd/lockd.h>
+#include <linux/lockd/bind.h>
 
 #include "internal.h"
 #include "nfs4_fs.h"
@@ -284,8 +284,12 @@ shutdown_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (!IS_ERR(server->client_acl))
 		shutdown_client(server->client_acl);
 
-	if (server->nlm_host)
-		shutdown_client(server->nlm_host->h_rpcclnt);
+	if (server->nlm_host) {
+		struct rpc_clnt *nlm_clnt = nlmclnt_rpc_clnt(server->nlm_host);
+
+		if (nlm_clnt)
+			shutdown_client(nlm_clnt);
+	}
 out:
 	shutdown_nfs_client(server->nfs_client);
 	return count;
-- 
2.52.0