- djm@cvs.openbsd.org 2010/01/30 02:54:53

[openssh.git] / README.privsep

diff --git a/README.privsep b/README.privsep
index 3ce37bf229903c2358d01e348fda9665fb20d9c6..b8c633b7a090fd09987c0fd388685027490d2ffc 100644 (file)
--- a/README.privsep
+++ b/README.privsep
@@ -1,26 +1,31 @@
 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.  
+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).
 
-When privsep is enabled, the pre-authentication sshd process will
+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.  You should do something like the following to
-prepare the privsep preauth environment:
+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 sshd
-
-If you are on UnixWare 7 or OpenUNIX 8 do this additional step.
-       # ln /usr/lib/.ns.so /usr/lib/ns.so.1
+       # useradd -g sshd -c 'sshd privsep' -d /var/empty -s /bin/false sshd
 
 /var/empty should not contain any files.
 
@@ -30,13 +35,15 @@ 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
-and mmap(MAP_ANON).
+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.
 
-PAM-enabled OpenSSH is known to function with privsep on Linux.  
-It does not function on HP-UX with a trusted system
-configuration.  PAMAuthenticationViaKbdInt does not function with
-privsep.
+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.