From b4f985b8f4d85913803d645dbad03a15ab5c09aa Mon Sep 17 00:00:00 2001
From: Dominik Brodowski <linux@dominikbrodowski.net>
Date: Tue, 23 Oct 2018 22:10:35 +0200
Subject: [PATCH] devtmpfs: use do_mount() instead of ksys_mount()

In devtmpfs, do_mount() can be called directly instead of complex wrapping
by ksys_mount():
- the first and third arguments are const strings in the kernel,
  and do not need to be copied over from userspace;
- the fifth argument is NULL, and therefore no page needs to be
  copied over from userspace;
- the second and fourth argument are passed through anyway.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
 drivers/base/devtmpfs.c | 6 +++---
 include/linux/device.h  | 4 ++--
 init/do_mounts.c        | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 30d0523014e0d..6cdbf15312387 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -359,7 +359,7 @@ static int handle_remove(const char *nodename, struct device *dev)
  * If configured, or requested by the commandline, devtmpfs will be
  * auto-mounted after the kernel mounted the root filesystem.
  */
-int devtmpfs_mount(const char *mntdir)
+int devtmpfs_mount(void)
 {
 	int err;
 
@@ -369,7 +369,7 @@ int devtmpfs_mount(const char *mntdir)
 	if (!thread)
 		return 0;
 
-	err = ksys_mount("devtmpfs", mntdir, "devtmpfs", MS_SILENT, NULL);
+	err = do_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 	else
@@ -394,7 +394,7 @@ static int devtmpfsd(void *p)
 	*err = ksys_unshare(CLONE_NEWNS);
 	if (*err)
 		goto out;
-	*err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
+	*err = do_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
 	if (*err)
 		goto out;
 	ksys_chdir("/.."); /* will traverse into overmounted root */
diff --git a/include/linux/device.h b/include/linux/device.h
index e226030c1df3c..96ff76731e93d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1666,11 +1666,11 @@ extern bool kill_device(struct device *dev);
 #ifdef CONFIG_DEVTMPFS
 extern int devtmpfs_create_node(struct device *dev);
 extern int devtmpfs_delete_node(struct device *dev);
-extern int devtmpfs_mount(const char *mntdir);
+extern int devtmpfs_mount(void);
 #else
 static inline int devtmpfs_create_node(struct device *dev) { return 0; }
 static inline int devtmpfs_delete_node(struct device *dev) { return 0; }
-static inline int devtmpfs_mount(const char *mountpoint) { return 0; }
+static inline int devtmpfs_mount(void) { return 0; }
 #endif
 
 /* drivers/base/power/shutdown.c */
diff --git a/init/do_mounts.c b/init/do_mounts.c
index af9cda887a23f..43f6d098c8806 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -670,7 +670,7 @@ void __init prepare_namespace(void)
 
 	mount_root();
 out:
-	devtmpfs_mount("dev");
+	devtmpfs_mount();
 	ksys_mount(".", "/", NULL, MS_MOVE, NULL);
 	ksys_chroot(".");
 }
-- 
2.39.5