init: add an init_chroot helper

Add a simple helper to chroot with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_chroot.

Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index e48aaba..eac184e 100644 (file)
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -413,7 +413,7 @@ static int __init devtmpfs_setup(void *p)
        if (err)
                goto out;
        init_chdir("/.."); /* will traverse into overmounted root */
-       ksys_chroot(".");
+       init_chroot(".");
 out:
        *(int *)p = err;
        complete(&setup_done);

diff --git a/fs/init.c b/fs/init.c
index 64d4e12..2c78f24 100644 (file)
--- a/fs/init.c
+++ b/fs/init.c
@@ -9,6 +9,7 @@
 #include <linux/fs.h>
 #include <linux/fs_struct.h>
 #include <linux/init_syscalls.h>
+#include <linux/security.h>
 #include "internal.h"
 
 int __init init_mount(const char *dev_name, const char *dir_name,
@@ -54,6 +55,29 @@ int __init init_chdir(const char *filename)
        return error;
 }
 
+int __init init_chroot(const char *filename)
+{
+       struct path path;
+       int error;
+
+       error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
+       if (error)
+               return error;
+       error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
+       if (error)
+               goto dput_and_out;
+       error = -EPERM;
+       if (!ns_capable(current_user_ns(), CAP_SYS_CHROOT))
+               goto dput_and_out;
+       error = security_path_chroot(&path);
+       if (error)
+               goto dput_and_out;
+       set_fs_root(current->fs, &path);
+dput_and_out:
+       path_put(&path);
+       return error;
+}
+
 int __init init_unlink(const char *pathname)
 {
        return do_unlinkat(AT_FDCWD, getname_kernel(pathname));

diff --git a/fs/open.c b/fs/open.c
index 723e0ac..f62f475 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -530,7 +530,7 @@ out:
        return error;
 }
 
-int ksys_chroot(const char __user *filename)
+SYSCALL_DEFINE1(chroot, const char __user *, filename)
 {
        struct path path;
        int error;
@@ -563,11 +563,6 @@ out:
        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;

diff --git a/include/linux/init_syscalls.h b/include/linux/init_syscalls.h
index 1e84591..e07099a 100644 (file)
--- a/include/linux/init_syscalls.h
+++ b/include/linux/init_syscalls.h
@@ -4,5 +4,6 @@ int __init init_mount(const char *dev_name, const char *dir_name,
                const char *type_page, unsigned long flags, void *data_page);
 int __init init_umount(const char *name, int flags);
 int __init init_chdir(const char *filename);
+int __init init_chroot(const char *filename);
 int __init init_unlink(const char *pathname);
 int __init init_rmdir(const char *pathname);

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 31fa67f..e89d62e 100644 (file)
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1235,8 +1235,6 @@ asmlinkage long sys_ni_syscall(void);
  * Instead, use one of the functions which work equivalently, such as
  * the ksys_xyzyyz() functions prototyped below.
  */
-
-int ksys_chroot(const char __user *filename);
 ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count);
 int ksys_fchown(unsigned int fd, uid_t user, gid_t group);
 ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count);

diff --git a/init/do_mounts.c b/init/do_mounts.c
index a7581c6..b5f9604 100644 (file)
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -629,7 +629,7 @@ void __init prepare_namespace(void)
 out:
        devtmpfs_mount();
        init_mount(".", "/", NULL, MS_MOVE, NULL);
-       ksys_chroot(".");
+       init_chroot(".");
 }
 
 static bool is_tmpfs;

diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index 04627fd..a6b447b 100644 (file)
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -63,7 +63,7 @@ static int __init init_linuxrc(struct subprocess_info *info, struct cred *new)
        /* move initrd over / and chdir/chroot in initrd root */
        init_chdir("/root");
        init_mount(".", "/", NULL, MS_MOVE, NULL);
-       ksys_chroot(".");
+       init_chroot(".");
        ksys_setsid();
        return 0;
 }
@@ -101,7 +101,7 @@ static void __init handle_initrd(void)
        /* move initrd to rootfs' /old */
        init_mount("..", ".", NULL, MS_MOVE, NULL);
        /* switch root and cwd back to / of rootfs */
-       ksys_chroot("..");
+       init_chroot("..");
 
        if (new_decode_dev(real_root_dev) == Root_RAM0) {
                init_chdir("/old");