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Subject[PATCH 066/109] fs: add ksys_mount() helper; remove in-kernel calls to sys_mount()
Date
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: Dominik Brodowski <linux@dominikbrodowski.net>
---
drivers/base/devtmpfs.c | 5 +++--
fs/namespace.c | 10 ++++++++--
include/linux/syscalls.h | 3 +++
init/do_mounts.c | 4 ++--
init/do_mounts_initrd.c | 6 +++---
5 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 50025d7959cb..4afb04686c8e 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -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 */
diff --git a/fs/namespace.c b/fs/namespace.c
index 9d1374ab6e06..642b8b229944 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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
*
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 6ab7ed71a8b6..3a9f9c534624 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -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
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 7cf4f6dafd5f..eb768de43d84 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -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(".");
}

diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index 53d4f0f326e7..7868a6039fb4 100644
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -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 {
--
2.16.3
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