sunrpc: make debugfs file creation failure non-fatal

v2: gracefully handle the case where some dentry pointers end up NULL
    and be more dilligent about zeroing out dentry pointers

We currently have a problem that SELinux policy is being enforced when
creating debugfs files. If a debugfs file is created as a side effect of
doing some syscall, then that creation can fail if the SELinux policy
for that process prevents it.

This seems wrong. We don't do that for files under /proc, for instance,
so Bruce has proposed a patch to fix that.

While discussing that patch however, Greg K.H. stated:

    "No kernel code should care / fail if a debugfs function fails, so
     please fix up the sunrpc code first."

This patch converts all of the sunrpc debugfs setup code to be void
return functins, and the callers to not look for errors from those
functions.

This should allow rpc_clnt and rpc_xprt creation to work, even if the
kernel fails to create debugfs files for some reason.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

include/linux/sunrpc/debug.h

@@ -60,17 +60,17 @@ struct rpc_xprt;
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 void		rpc_register_sysctl(void);
 void		rpc_unregister_sysctl(void);
-int		sunrpc_debugfs_init(void);
+void		sunrpc_debugfs_init(void);
 void		sunrpc_debugfs_exit(void);
-int		rpc_clnt_debugfs_register(struct rpc_clnt *);
+void		rpc_clnt_debugfs_register(struct rpc_clnt *);
 void		rpc_clnt_debugfs_unregister(struct rpc_clnt *);
-int		rpc_xprt_debugfs_register(struct rpc_xprt *);
+void		rpc_xprt_debugfs_register(struct rpc_xprt *);
 void		rpc_xprt_debugfs_unregister(struct rpc_xprt *);
 #else
-static inline int
+static inline void
 sunrpc_debugfs_init(void)
 {
-	return 0;
+	return;
 }
 
 static inline void
@@ -79,10 +79,10 @@ sunrpc_debugfs_exit(void)
 	return;
 }
 
-static inline int
+static inline void
 rpc_clnt_debugfs_register(struct rpc_clnt *clnt)
 {
-	return 0;
+	return;
 }
 
 static inline void
@@ -91,10 +91,10 @@ rpc_clnt_debugfs_unregister(struct rpc_clnt *clnt)
 	return;
 }
 
-static inline int
+static inline void
 rpc_xprt_debugfs_register(struct rpc_xprt *xprt)
 {
-	return 0;
+	return;
 }
 
 static inline void

net/sunrpc/clnt.c

@@ -303,9 +303,7 @@ static int rpc_client_register(struct rpc_clnt *clnt,
 	struct super_block *pipefs_sb;
 	int err;
 
-	err = rpc_clnt_debugfs_register(clnt);
-	if (err)
-		return err;
+	rpc_clnt_debugfs_register(clnt);
 
 	pipefs_sb = rpc_get_sb_net(net);
 	if (pipefs_sb) {

net/sunrpc/debugfs.c

@@ -129,48 +129,52 @@ static const struct file_operations tasks_fops = {
 	.release	= tasks_release,
 };
 
-int
+void
 rpc_clnt_debugfs_register(struct rpc_clnt *clnt)
 {
-	int len, err;
+	int len;
 	char name[24]; /* enough for "../../rpc_xprt/ + 8 hex digits + NULL */
+	struct rpc_xprt *xprt;
 
 	/* Already registered? */
-	if (clnt->cl_debugfs)
-		return 0;
+	if (clnt->cl_debugfs || !rpc_clnt_dir)
+		return;
 
 	len = snprintf(name, sizeof(name), "%x", clnt->cl_clid);
 	if (len >= sizeof(name))
-		return -EINVAL;
+		return;
 
 	/* make the per-client dir */
 	clnt->cl_debugfs = debugfs_create_dir(name, rpc_clnt_dir);
 	if (!clnt->cl_debugfs)
-		return -ENOMEM;
+		return;
 
 	/* make tasks file */
-	err = -ENOMEM;
 	if (!debugfs_create_file("tasks", S_IFREG | S_IRUSR, clnt->cl_debugfs,
 				 clnt, &tasks_fops))
 		goto out_err;
 
-	err = -EINVAL;
 	rcu_read_lock();
+	xprt = rcu_dereference(clnt->cl_xprt);
+	/* no "debugfs" dentry? Don't bother with the symlink. */
+	if (!xprt->debugfs) {
+		rcu_read_unlock();
+		return;
+	}
 	len = snprintf(name, sizeof(name), "../../rpc_xprt/%s",
-			rcu_dereference(clnt->cl_xprt)->debugfs->d_name.name);
+			xprt->debugfs->d_name.name);
 	rcu_read_unlock();
+
 	if (len >= sizeof(name))
 		goto out_err;
 
-	err = -ENOMEM;
 	if (!debugfs_create_symlink("xprt", clnt->cl_debugfs, name))
 		goto out_err;
 
-	return 0;
+	return;
 out_err:
 	debugfs_remove_recursive(clnt->cl_debugfs);
 	clnt->cl_debugfs = NULL;
-	return err;
 }
 
 void
@@ -226,33 +230,33 @@ static const struct file_operations xprt_info_fops = {
 	.release	= xprt_info_release,
 };
 
-int
+void
 rpc_xprt_debugfs_register(struct rpc_xprt *xprt)
 {
 	int len, id;
 	static atomic_t	cur_id;
 	char		name[9]; /* 8 hex digits + NULL term */
 
+	if (!rpc_xprt_dir)
+		return;
+
 	id = (unsigned int)atomic_inc_return(&cur_id);
 
 	len = snprintf(name, sizeof(name), "%x", id);
 	if (len >= sizeof(name))
-		return -EINVAL;
+		return;
 
 	/* make the per-client dir */
 	xprt->debugfs = debugfs_create_dir(name, rpc_xprt_dir);
 	if (!xprt->debugfs)
-		return -ENOMEM;
+		return;
 
 	/* make tasks file */
 	if (!debugfs_create_file("info", S_IFREG | S_IRUSR, xprt->debugfs,
 				 xprt, &xprt_info_fops)) {
 		debugfs_remove_recursive(xprt->debugfs);
 		xprt->debugfs = NULL;
-		return -ENOMEM;
 	}
-
-	return 0;
 }
 
 void
@@ -266,14 +270,17 @@ void __exit
 sunrpc_debugfs_exit(void)
 {
 	debugfs_remove_recursive(topdir);
+	topdir = NULL;
+	rpc_clnt_dir = NULL;
+	rpc_xprt_dir = NULL;
 }
 
-int __init
+void __init
 sunrpc_debugfs_init(void)
 {
 	topdir = debugfs_create_dir("sunrpc", NULL);
 	if (!topdir)
-		goto out;
+		return;
 
 	rpc_clnt_dir = debugfs_create_dir("rpc_clnt", topdir);
 	if (!rpc_clnt_dir)
@@ -283,10 +290,9 @@ sunrpc_debugfs_init(void)
 	if (!rpc_xprt_dir)
 		goto out_remove;
 
-	return 0;
+	return;
 out_remove:
 	debugfs_remove_recursive(topdir);
 	topdir = NULL;
-out:
-	return -ENOMEM;
+	rpc_clnt_dir = NULL;
 }

net/sunrpc/sunrpc_syms.c

@@ -98,19 +98,14 @@ init_sunrpc(void)
 	if (err)
 		goto out4;
 
-	err = sunrpc_debugfs_init();
-	if (err)
-		goto out5;
-
+	sunrpc_debugfs_init();
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 	rpc_register_sysctl();
 #endif
 	svc_init_xprt_sock();	/* svc sock transport */
 	init_socket_xprt();	/* clnt sock transport */
 	return 0;
 
-out5:
-	unregister_rpc_pipefs();
 out4:
 	unregister_pernet_subsys(&sunrpc_net_ops);
 out3:

net/sunrpc/xprt.c

@@ -1331,7 +1331,6 @@ static void xprt_init(struct rpc_xprt *xprt, struct net *net)
  */
 struct rpc_xprt *xprt_create_transport(struct xprt_create *args)
 {
-	int err;
 	struct rpc_xprt	*xprt;
 	struct xprt_class *t;
 
@@ -1372,11 +1371,7 @@ struct rpc_xprt *xprt_create_transport(struct xprt_create *args)
 		return ERR_PTR(-ENOMEM);
 	}
 
-	err = rpc_xprt_debugfs_register(xprt);
-	if (err) {
-		xprt_destroy(xprt);
-		return ERR_PTR(err);
-	}
+	rpc_xprt_debugfs_register(xprt);
 
 	dprintk("RPC:       created transport %p with %u slots\n", xprt,
 			xprt->max_reqs);