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Viewing changes to dracut-module/cmdline-mandos.sh

  • Committer: Teddy Hogeborn
  • Date: 2015-03-10 18:03:38 UTC
  • mto: (237.7.304 trunk)
  • mto: This revision was merged to the branch mainline in revision 325.
  • Revision ID: teddy@recompile.se-20150310180338-pcxw6r2qmw9k6br9
Add ":!RSA" to GnuTLS priority string, to disallow non-DHE kx.

If Mandos was somehow made to use a non-ephemeral Diffie-Hellman key
exchange algorithm in the TLS handshake, any saved network traffic
could then be decrypted later if the Mandos client key was obtained.
By default, Mandos uses ephemeral DH key exchanges which does not have
this problem, but a non-ephemeral key exchange algorithm was still
enabled by default.  The simplest solution is to simply turn that off,
which ensures that Mandos will always use ephemeral DH key exchanges.

There is a "PFS" priority string specifier, but we can't use it because:

1. Security-wise, it is a mix between "NORMAL" and "SECURE128" - it
   enables a lot more algorithms than "SECURE256".

2. It is only available since GnuTLS 3.2.4.

Thanks to Andreas Fischer <af@bantuX.org> for reporting this issue.

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dracut-module/cmdline-mandos.sh
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#!/bin/sh
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#
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# This file should be present in the root file system directory
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# /usr/lib/dracut/modules.d/90mandos.  When dracut creates the
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# initramfs image, dracut will run the "module-setup.sh" file in the
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# same directory, which (when *not* using the "systemd" dracut module)
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# will copy this file ("cmdline-mandos.sh") into the initramfs as
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# "/lib/dracut/hooks/cmdline/20-cmdline-mandos.sh".
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# 
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# Despite the above #!/bin/sh line and the executable flag, this file
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# is not executed; this file is sourced by the /init script in the
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# initramfs image created by dracut.
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if getargbool 1 mandos && [ -e /lib/dracut-crypt-lib.sh ]; then
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    cat >> /lib/dracut-crypt-lib.sh <<- "EOF"
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        ask_for_password(){
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            local cmd; local prompt; local tries=3
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            local ply_cmd; local ply_prompt; local ply_tries=3
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            local tty_cmd; local tty_prompt; local tty_tries=3
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            local ret
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            while [ $# -gt 0 ]; do
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                case "$1" in
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                    --cmd) ply_cmd="$2"; tty_cmd="$2"; shift;;
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                    --ply-cmd) ply_cmd="$2"; shift;;
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                    --tty-cmd) tty_cmd="$2"; shift;;
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                    --prompt) ply_prompt="$2"; tty_prompt="$2"; shift;;
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                    --ply-prompt) ply_prompt="$2"; shift;;
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                    --tty-prompt) tty_prompt="$2"; shift;;
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                    --tries) ply_tries="$2"; tty_tries="$2"; shift;;
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                    --ply-tries) ply_tries="$2"; shift;;
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                    --tty-tries) tty_tries="$2"; shift;;
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                    --tty-echo-off) tty_echo_off=yes;;
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                    -*) :;;
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                esac
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                shift
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            done
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            if [ -z "$ply_cmd" ]; then
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                ply_cmd="$tty_cmd"
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            fi
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            # Extract device and luksname from $ply_cmd
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            set -- $ply_cmd
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            shift
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            for arg in "$@"; do
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                case "$arg" in
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                    -*) :;;
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                    *)
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                        if [ -z "$device" ]; then
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                            device="$arg"
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                        else
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                            luksname="$arg"
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                            break
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                        fi
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                        ;;
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                esac
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            done
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            { flock -s 9;
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              if [ -z "$ply_prompt" ]; then
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                  if [ -z "$tty_prompt" ]; then
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                      CRYPTTAB_SOURCE="$device" cryptsource="$device" CRYPTTAB_NAME="$luksname" crypttarget="$luksname" /lib/mandos/plugin-runner --config-file=/etc/mandos/plugin-runner.conf | $ply_cmd
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                  else
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                      CRYPTTAB_SOURCE="$device" cryptsource="$device" CRYPTTAB_NAME="$luksname" crypttarget="$luksname" /lib/mandos/plugin-runner --options-for=password-prompt:--prompt="${tty_prompt}" --config-file=/etc/mandos/plugin-runner.conf | $ply_cmd
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                  fi
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              else
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                  if [ -z "$tty_prompt" ]; then
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                      CRYPTTAB_SOURCE="$device" cryptsource="$device" CRYPTTAB_NAME="$luksname" crypttarget="$luksname" /lib/mandos/plugin-runner --options-for=plymouth:--prompt="${ply_prompt}" --config-file=/etc/mandos/plugin-runner.conf | $ply_cmd
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                  else
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                      CRYPTTAB_SOURCE="$device" cryptsource="$device" CRYPTTAB_NAME="$luksname" crypttarget="$luksname" /lib/mandos/plugin-runner --options-for=password-prompt:--prompt="${tty_prompt}" --options-for=plymouth:--prompt="${ply_prompt}" --config-file=/etc/mandos/plugin-runner.conf | $ply_cmd
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                  fi
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              fi
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            } 9>/.console_lock
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        }
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        EOF
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fi