The chroot system call changes the root of the calling process.
The
fs/open.c
file provides the definitions for several file related syscalls, including:
chroottruncate (which sets a file to a specified length)access (which checks if the calling process can access the specified file)chdir (which changes the working directory of the calling process)chmod (which sets file permissions)chown (which sets file user and group ownership)opencloseSeveral system calls, including clone, unshare, and setns
control the namespaces to which a process belongs.
The
kernel/fork.c
file defines several syscalls related to forking new processes, including the
fork,
vfork, and
clone syscalls.
Each of these syscalls calls the
kernel_clone()
function, which is the main fork-routine of the Linux kernel (and is also called when the kernel creates a new kernel thread).
The kernel_clone() function then calls the
copy_process()
function, which performs the bulk of the work of copying a process.
The
kernel/fork.c
file also provides the
unshare
syscall, which itself calls the
ksys_unshare()
function, which performs the bulk of the work of unsharing namespaces.
The
kernel/nsproxy.c
file provides the
copy_namespaces()
function which is called by copy_process() function, as well as the
unshare_nsproxy_namespaces()
function, which is called by ksys_unshare().
Both of these functions call the
create_new_namespaces()
function, which is also in the
kernel/nsproxy.c
file, and runs various functions to create new namespaces, depending on the namespace types specified.
Relevant to the namespaces discussed today are:
cpy_mnt_ns()
in the
fs/namespace.c
file, which copies a mount namespace to a new one.
copy_utsname()
in the
kernel/utsname.c
file, which copies a UTS namespace to a new one.
copy_ipcs()
in the
ipc/namespace.c
file, which copies an IPC namespace to a new one.
copy_pid_ns()
in the
kernel/pid_namespace.c
file, which copies a PID namespace to a new one.
The
kernel/nsproxy.c
file also provides the
setns
syscall, which moves the calling process into the specified, already-existing, namespace.
The
task_struct
structure, defined in
include/linux/sched.h,
has as an element a pointer to an
nsproxy
structure, defined in the
include/linux/nsproxy.h
header.
This structure associates the process with each of the namespace types discussed today.
The proc pseudo-filesystem provides detailed information and statistics about each active process,
including information about namespace membership.
The
include/linux/proc_fs.h
header file declares the constants and structures used by the proc filesystem.
The
proc_fs_info
struct defined in this file contains information about a proc filesystem associated with a PID namespace.
The
pid_namespace
struct, which is a member of proc_fs_info, is defined in the
include/linux/proc_fs.h
header file.
The
fs/proc
directory includes the source code files for its kernel-backed functionality.
Of particular interest is the
fs/proc/namespaces.c
file, which retrieves namespace membership for the /proc/PID/ns directory.