jail(2)

NAME

Standard C Library (libc, -lc)

#include <sys/param.h>
#include <sys/jail.h>
int
jail(struct jail *jail);
int
jail_attach(int jid);

The jail() system call sets up a jail and locks the current
process in it.
The argument is a pointer to a structure describing the
prison:: struct jail {
u_int32_t version;
char *path;
char *hostname;
u_int32_t ip_number;; };
``version'' defines the version of the API in use. It
should be set to zero at this time.
The ``path'' pointer should be set to the directory which is
to be the root of the prison.
The ``hostname'' pointer can be set to the hostname of the
prison. This can be changed from the inside of the prison.
The ``ip_number'' can be set to the IP number assigned to
the prison.
The jail_attach() system call attaches the current process
to an existing jail, identified by jid.

Once a process has been put in a prison, it and its descen
dants cannot escape the prison.
Inside the prison, the concept of ``superuser'' is very di
luted. In general, it can be assumed that nothing can be mangled from in
side a prison which does not exist entirely inside that prison. For in
stance the directory tree below ``path'' can be manipulated all the
ways a root can normally do it, including ``rm -rf /*'' but new device spe
cial nodes cannot be created because they reference shared resources (the
device drivers in the kernel). The effective ``securelevel'' for a
process is the greater of the global ``securelevel'' or, if present,
the per-jail ``securelevel''.
All IP activity will be forced to happen to/from the IP num
ber specified, which should be an alias on one of the network interfaces.
It is possible to identify a process as jailed by examining ``/proc/<pid>/status'': it will show a field near the end of
the line, either as a single hyphen for a process at large, or the
hostname currently set for the prison for jailed processes.

The jail() system call will fail if: