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fs: add ksys_chroot() helper; remove-in kernel calls to sys_chroot()

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Using this helper allows us to avoid the in-kernel calls to the
sys_chroot() 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_chroot().

In the near future, the fs-external callers of ksys_chroot() should be
converted to use kern_path()/set_fs_root() directly. Then ksys_chroot()
can be moved within sys_chroot() again.

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>
This commit is contained in:
Dominik Brodowski 2018-03-11 11:34:41 +01:00
parent c7248321a3
commit a16fe33ab5
5 changed files with 11 additions and 5 deletions
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2
drivers/base/devtmpfs.c
View File

@ -387,7 +387,7 @@ static int devtmpfsd(void *p)
if (*err)
goto out;
sys_chdir("/.."); /* will traverse into overmounted root */
sys_chroot(".");
ksys_chroot(".");
complete(&setup_done);
while (1) {
spin_lock(&req_lock);

7
fs/open.c
View File

@ -479,7 +479,7 @@ SYSCALL_DEFINE1(fchdir, unsigned int, fd)
return error;
}
SYSCALL_DEFINE1(chroot, const char __user *, filename)
int ksys_chroot(const char __user *filename)
{
struct path path;
int error;
@ -512,6 +512,11 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
return error;
}
SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
return ksys_chroot(filename);
}
static int chmod_common(const struct path *path, umode_t mode)
{
struct inode *inode = path->dentry->d_inode;

1
include/linux/syscalls.h
View File

@ -950,5 +950,6 @@ int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,
unsigned long flags, void __user *data);
int ksys_umount(char __user *name, int flags);
int ksys_dup(unsigned int fildes);
int ksys_chroot(const char __user *filename);
#endif

2
init/do_mounts.c
View File

@ -600,7 +600,7 @@ void __init prepare_namespace(void)
out:
devtmpfs_mount("dev");
ksys_mount(".", "/", NULL, MS_MOVE, NULL);
sys_chroot(".");
ksys_chroot(".");
}
static bool is_tmpfs;

4
init/do_mounts_initrd.c
View File

@ -44,7 +44,7 @@ static int init_linuxrc(struct subprocess_info *info, struct cred *new)
/* move initrd over / and chdir/chroot in initrd root */
sys_chdir("/root");
ksys_mount(".", "/", NULL, MS_MOVE, NULL);
sys_chroot(".");
ksys_chroot(".");
sys_setsid();
return 0;
}
@ -83,7 +83,7 @@ static void __init handle_initrd(void)
/* move initrd to rootfs' /old */
ksys_mount("..", ".", NULL, MS_MOVE, NULL);
/* switch root and cwd back to / of rootfs */
sys_chroot("..");
ksys_chroot("..");
if (new_decode_dev(real_root_dev) == Root_RAM0) {
sys_chdir("/old");