Commit 312db1aa authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

fs: add ksys_mount() helper; remove in-kernel calls to sys_mount() 

Using this helper allows us to avoid the in-kernel calls to the sys_mount()
syscall. The ksys_ prefix denotes that this function is meant as a drop-in
replacement for the syscall. In particular, it uses the same calling
convention as sys_mount().

In the near future, all callers of ksys_mount() should be converted to call
do_mount() directly.

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net



Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent ab0d1e85

drivers/base/devtmpfs.c

+3 −2
Original line number Diff line number Diff line
@@ -356,7 +356,8 @@ int devtmpfs_mount(const char *mntdir) 
	if (!thread)

		return 0;



	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);

	err = ksys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT,

			 NULL);

	if (err)

		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);

	else
@@ -382,7 +383,7 @@ static int devtmpfsd(void *p) 
	*err = sys_unshare(CLONE_NEWNS);

	if (*err)

		goto out;

	*err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);

	*err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);

	if (*err)

		goto out;

	sys_chdir("/.."); /* will traverse into overmounted root */

fs/namespace.c

+8 −2
Original line number Diff line number Diff line
@@ -3032,8 +3032,8 @@ struct dentry *mount_subtree(struct vfsmount *mnt, const char *name) 
}

EXPORT_SYMBOL(mount_subtree);



SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,

		char __user *, type, unsigned long, flags, void __user *, data)

int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,

	       unsigned long flags, void __user *data)

{

	int ret;

	char *kernel_type;
@@ -3066,6 +3066,12 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, 
	return ret;

}



SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,

		char __user *, type, unsigned long, flags, void __user *, data)

{

	return ksys_mount(dev_name, dir_name, type, flags, data);

}



/*

 * Return true if path is reachable from root

 *

include/linux/syscalls.h

+3 −0
Original line number Diff line number Diff line
@@ -946,4 +946,7 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags, 
 * the ksys_xyzyyz() functions prototyped below.

 */



int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,

	       unsigned long flags, void __user *data);



#endif

init/do_mounts.c

+2 −2
Original line number Diff line number Diff line
@@ -363,7 +363,7 @@ static void __init get_fs_names(char *page) 
static int __init do_mount_root(char *name, char *fs, int flags, void *data)

{

	struct super_block *s;

	int err = sys_mount(name, "/root", fs, flags, data);

	int err = ksys_mount(name, "/root", fs, flags, data);

	if (err)

		return err;
@@ -599,7 +599,7 @@ void __init prepare_namespace(void) 
	mount_root();

out:

	devtmpfs_mount("dev");

	sys_mount(".", "/", NULL, MS_MOVE, NULL);

	ksys_mount(".", "/", NULL, MS_MOVE, NULL);

	sys_chroot(".");

}

init/do_mounts_initrd.c

+3 −3
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ static int init_linuxrc(struct subprocess_info *info, struct cred *new) 
	sys_dup(0);

	/* move initrd over / and chdir/chroot in initrd root */

	sys_chdir("/root");

	sys_mount(".", "/", NULL, MS_MOVE, NULL);

	ksys_mount(".", "/", NULL, MS_MOVE, NULL);

	sys_chroot(".");

	sys_setsid();

	return 0;
@@ -81,7 +81,7 @@ static void __init handle_initrd(void) 
	current->flags &= ~PF_FREEZER_SKIP;



	/* move initrd to rootfs' /old */

	sys_mount("..", ".", NULL, MS_MOVE, NULL);

	ksys_mount("..", ".", NULL, MS_MOVE, NULL);

	/* switch root and cwd back to / of rootfs */

	sys_chroot("..");
@@ -95,7 +95,7 @@ static void __init handle_initrd(void) 
	mount_root();



	printk(KERN_NOTICE "Trying to move old root to /initrd ... ");

	error = sys_mount("/old", "/root/initrd", NULL, MS_MOVE, NULL);

	error = ksys_mount("/old", "/root/initrd", NULL, MS_MOVE, NULL);

	if (!error)

		printk("okay\n");

	else {