58 lines
2.3 KiB
Plaintext
58 lines
2.3 KiB
Plaintext
Privilege separation, or privsep, is an experimental feature in
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OpenSSH in which operations that require root privilege are performed
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by a separate privileged monitor process. Its purpose is to prevent
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privilege escalation by containing corruption to an unprivileged
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process. More information is available at:
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http://www.citi.umich.edu/u/provos/ssh/privsep.html
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Privilege separation is not enabled by default, and may be enabled by
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specifying "UsePrivilegeSeparation yes" in sshd_config; see the
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UsePrivilegeSeparation option in sshd(8).
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When privsep is enabled, the pre-authentication sshd process will
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chroot(2) to "/var/empty" and change its privileges to the "sshd" user
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and its primary group. You should do something like the following to
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prepare the privsep preauth environment:
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# mkdir /var/empty
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# chown root:sys /var/empty
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# chmod 755 /var/empty
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# groupadd sshd
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# useradd -g sshd sshd
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If you are on UnixWare 7 or OpenUNIX 8 do this additional step.
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# ln /usr/lib/.ns.so /usr/lib/ns.so.1
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/var/empty should not contain any files.
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configure supports the following options to change the default
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privsep user and chroot directory:
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--with-privsep-path=xxx Path for privilege seperation chroot
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--with-privsep-user=user Specify non-privileged user for privilege separation
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Privsep requires operating system support for file descriptor passing
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and mmap(MAP_ANON).
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PAM-enabled OpenSSH is known to function with privsep on Linux and
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Solaris 8. It does not function on HP-UX with a trusted system
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configuration. PAMAuthenticationViaKbdInt does not function with
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privsep.
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Note that for a normal interactive login with a shell, enabling privsep
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will require 1 additional process per login session.
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Given the following process listing (from HP-UX):
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UID PID PPID C STIME TTY TIME COMMAND
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root 1005 1 0 10:45:17 ? 0:08 /opt/openssh/sbin/sshd -u0
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root 6917 1005 0 15:19:16 ? 0:00 sshd: stevesk [priv]
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stevesk 6919 6917 0 15:19:17 ? 0:03 sshd: stevesk@2
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stevesk 6921 6919 0 15:19:17 pts/2 0:00 -bash
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process 1005 is the sshd process listening for new connections.
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process 6917 is the privileged monitor process, 6919 is the user owned
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sshd process and 6921 is the shell process.
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$Id: README.privsep,v 1.4 2002/05/14 03:50:38 tim Exp $
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