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authorKevin Steves <stevesk@pobox.com>2002-05-13 03:57:04 +0000
committerKevin Steves <stevesk@pobox.com>2002-05-13 03:57:04 +0000
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+Privilege separation, or privsep, is an experimental feature in
+OpenSSH in 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 not enabled by default, and may be enabled by
+specifying "UsePrivilegeSeparation yes" in sshd_config; see the
+UsePrivilegeSeparation option in sshd(8).
+
+When privsep is enabled, the pre-authentication sshd process will
+chroot(2) to "/var/empty" and change its privileges to the "sshd" user
+and its primary group. 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 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 seperation chroot
+ --with-privsep-user=user Specify non-privileged user for privilege separation
+
+Privsep requires operating system support for file descriptor passing
+and mmap(MAP_ANON).
+
+PAM currently only works with privsep on Linux. It does not function
+on Solaris or HP-UX. PAMAuthenticationViaKbdInt does not function with
+privsep.
+
+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.
+
+$Id: README.privsep,v 1.1 2002/05/13 03:57:04 stevesk Exp $