Ubuntu Manpage: reducecap - The reducecap utility is used to lower the capability ceiling of a process and child process.

Provided by: util-vserver_0.30.216-pre3120-1.4_amd64

NAME

       reducecap - The reducecap utility is used to lower the capability ceiling of a process and child process.

SYNTAX

       reducecap [options] <command arguments>

DESCRIPTION

       The reducecap utility is used to lower the capability ceiling of a process and child process. Even setuid
       program won't be able to grab more capabilities.

OPTIONS

--secure Removes all dangerous capabilities from the process executed.Specificly it removes:
CAP_LINUX_IMMUTABLE CAP_NET_BROADCAST CAP_NET_ADMIN, CAP_NET_RAW CAP_IPC_LOCK CAP_IPC_OWNER
CAP_SYS_MODULE CAP_SYS_RAWIO CAP_SYS_PACCT CAP_SYS_ADMIN CAP_SYS_BOOT CAP_SYS_NICE
CAP_SYS_RESOURCE CAP_SYS_TIME CAP_MKNOD.

Leaving the following capabilities: CAP_CHOWN CAP_DAC_OVERRIDE CAP_DAC_READ_SEARCH CAP_FOWNER
CAP_FSETID CAP_KILL CAP_SETGID CAP_SETUID CAP_NET_BIND_SERVICE CAP_SYS_CHROOT CAP_SYS_PTRACE
CAP_SYS_TTY_CONFIG CAP_LEASE CAP_QUOTACTL

--show Shows the current process capabilities.

--flag sets the security context flags. The option may be repeated several times. Here are the values:

lock: The security context can't be changed. The process is trapped in this context. This
is generally used for vservers because yoy do not want them to hide in new security
context.

sched: Each process in a security context contribute (lower) to the general priority of every
processes in the context. Mostly, all processes in a security context take as much CPU
together as one process not bound to this flag. Said again differently, a vserver having
100 active processes won't get more CPU than another vserver with a single active
process.

nproc: The "ulimit -u N" setting becomes global to the security context. It means the
security context is not allowed to have more than N processes.

private: No other processes, even root in security context 0, is allowed to enter this
security context. Once a security context is setup with this flag, it is on its own. This
also means that root in security context 0 won't be able to kill or interact with those
processes.

hideinfo: Hides various information in /proc.

--LINUX_IMMUTABLE

--NET_BIND_SERVICE

--NET_BROADCAST

--NET_ADMIN

--NET_RAW

--IPC_LOCK

--IPC_OWNER

--SYS_MODULE

--SYS_RAWIO

--SYS_PACCT

--SYS_ADMIN

--SYS_BOOT

--SYS_NICE

--SYS_RESOURCE

--SYS_TIME

--MKNOD

All these options remove one capability. These options may be used after the --secure option to
remove more capabilities.

FILES

       /usr/sbin/reducecap

EXAMPLES

       #  You are not root now # What is the current capability ceiling cat /proc/self/status # The capBset line
       presents mostly 1s.  /usr/sbin/reducecap --secure /bin/sh cat /proc/self/status # The capBset  now  shows
       many  more  0s.   #  The  capEff  shows  all  0s,  you  have  no  privilege  now  #  We su to root su cat
       /proc/self/status # capEff is much better now, but there are still many 0s # Now we try to see if we  are
       really  root  tail  /var/log/messages  #  So  far  so  good,  we  see  the  content  /sbin/ifconfig  eth0
       /sbin/ifconfig eth0 down # No way, we can't configure  the  interface.  In  fact  #  we  have  lost  most
       privilege normally assigned to root exit

       Please contribute some more, if you feel it's important.

AUTHORS

       This  Man  page  was  written  by  Klavs  Klavsen <kl@vsen.dk> and based upon the helpful output from the
       program     itself     and     the      documentation      on      the      Virtual      Server      site
       <http://www.solucorp.qc.ca/miscprj/s_context.hc?prjstate=1&nodoc=0>