mirror of
git://anongit.mindrot.org/openssh.git
synced 2024-11-25 03:24:15 +08:00
adab758242
Since -portable switched to git, the CVS $Id tags are no longer being updated and are becoming increasingly misleading. Remove them.
62 lines
2.5 KiB
Plaintext
62 lines
2.5 KiB
Plaintext
Privilege separation, or privsep, is method in OpenSSH by which
|
|
operations that require root privilege are performed by a separate
|
|
privileged monitor process. Its purpose is to prevent privilege
|
|
escalation by containing corruption to an unprivileged process.
|
|
More information is available at:
|
|
http://www.citi.umich.edu/u/provos/ssh/privsep.html
|
|
|
|
Privilege separation is now enabled by default; see the
|
|
UsePrivilegeSeparation option in sshd_config(5).
|
|
|
|
On systems which lack mmap or anonymous (MAP_ANON) memory mapping,
|
|
compression must be disabled in order for privilege separation to
|
|
function.
|
|
|
|
When privsep is enabled, during the pre-authentication phase sshd will
|
|
chroot(2) to "/var/empty" and change its privileges to the "sshd" user
|
|
and its primary group. sshd is a pseudo-account that should not be
|
|
used by other daemons, and must be locked and should contain a
|
|
"nologin" or invalid shell.
|
|
|
|
You should do something like the following to prepare the privsep
|
|
preauth environment:
|
|
|
|
# mkdir /var/empty
|
|
# chown root:sys /var/empty
|
|
# chmod 755 /var/empty
|
|
# groupadd sshd
|
|
# useradd -g sshd -c 'sshd privsep' -d /var/empty -s /bin/false sshd
|
|
|
|
/var/empty should not contain any files.
|
|
|
|
configure supports the following options to change the default
|
|
privsep user and chroot directory:
|
|
|
|
--with-privsep-path=xxx Path for privilege separation chroot
|
|
--with-privsep-user=user Specify non-privileged user for privilege separation
|
|
|
|
Privsep requires operating system support for file descriptor passing.
|
|
Compression will be disabled on systems without a working mmap MAP_ANON.
|
|
|
|
PAM-enabled OpenSSH is known to function with privsep on AIX, FreeBSD,
|
|
HP-UX (including Trusted Mode), Linux, NetBSD and Solaris.
|
|
|
|
On Cygwin, Tru64 Unix, OpenServer, and Unicos only the pre-authentication
|
|
part of privsep is supported. Post-authentication privsep is disabled
|
|
automatically (so you won't see the additional process mentioned below).
|
|
|
|
Note that for a normal interactive login with a shell, enabling privsep
|
|
will require 1 additional process per login session.
|
|
|
|
Given the following process listing (from HP-UX):
|
|
|
|
UID PID PPID C STIME TTY TIME COMMAND
|
|
root 1005 1 0 10:45:17 ? 0:08 /opt/openssh/sbin/sshd -u0
|
|
root 6917 1005 0 15:19:16 ? 0:00 sshd: stevesk [priv]
|
|
stevesk 6919 6917 0 15:19:17 ? 0:03 sshd: stevesk@2
|
|
stevesk 6921 6919 0 15:19:17 pts/2 0:00 -bash
|
|
|
|
process 1005 is the sshd process listening for new connections.
|
|
process 6917 is the privileged monitor process, 6919 is the user owned
|
|
sshd process and 6921 is the shell process.
|