| 1 | #!/bin/sh -eu |
| 2 | # |
| 3 | # Short version of this script: |
| 4 | # curl -f -o /var/cache/exim/opendmarc.tlds https://publicsuffix.org/list/public_suffix_list.dat |
| 5 | # but run as Exim runtime user, writing to a place it can write to, and with |
| 6 | # sanity checks and atomic replacement. |
| 7 | # |
| 8 | # For now, we deliberately leave the invalid file around for analysis |
| 9 | # with .<pid> suffix. |
| 10 | # |
| 11 | # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~8< cut here >8~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 12 | # |
| 13 | # Create a cron-job as the Exim run-time user to invoke this daily, with a |
| 14 | # single parameter, 'cron'. Eg: |
| 15 | # |
| 16 | # 3 4 * * * /usr/local/sbin/renew-opendmarc-tlds.sh cron |
| 17 | # |
| 18 | # That will, at 3 minutes past the 4th hour (in whatever timezone cron is |
| 19 | # running it) invoke this script with 'cron'; we will then sleep between 10 and |
| 20 | # 50 seconds, before continuing. |
| 21 | # |
| 22 | # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~8< cut here >8~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 23 | # |
| 24 | # This should be "pretty portable"; the only things it depends upon are: |
| 25 | # * a POSIX shell which additionally implements 'local' (dash works) |
| 26 | # * the 'curl' command; change the fetch_candidate() function to replace that |
| 27 | # * the 'stat' command, to get the size of a file; else Perl |
| 28 | # + change size_of() if need be; it's defined per-OS |
| 29 | # * the 'hexdump' command and /dev/urandom existing |
| 30 | # + used when invoked with 'cron', to avoid retrieving on a minute boundary |
| 31 | # and contending with many other automated systems. |
| 32 | # + with bash/zsh, can replace with: $(( 10 + ( RANDOM % 40 ) )) |
| 33 | # + on Debian/Ubuntu systems, hexdump is in the 'bsdmainutils' package. |
| 34 | |
| 35 | # Consider putting an email address inside the parentheses, something like |
| 36 | # noc@example.org or other reachable address, so that if something goes wrong |
| 37 | # and the server operators need to step in, they can see from logs who to |
| 38 | # contact instead of just blocking your IP: |
| 39 | readonly CurlUserAgent='renew-opendmarc-tlds/0.1 (distributed with Exim)' |
| 40 | |
| 41 | # change this to your Exim run-time user (exim -n -bP exim_user) : |
| 42 | readonly RuntimeUser='_exim' |
| 43 | |
| 44 | # Do not make this a directory which untrusted users can write to: |
| 45 | readonly StateDir='/var/cache/exim' |
| 46 | |
| 47 | readonly URL='https://publicsuffix.org/list/public_suffix_list.dat' |
| 48 | |
| 49 | readonly TargetShortFile='opendmarc.tlds' |
| 50 | |
| 51 | # When replacing, new file must be at least this percentage the size of |
| 52 | # the old one or it's an error: |
| 53 | readonly MinNewSizeRation=90 |
| 54 | |
| 55 | # Each of these regexps must be matched by the file, or it's an error: |
| 56 | readonly MustExistRegexps=' |
| 57 | ^ac\.uk$ |
| 58 | ^org$ |
| 59 | ^tech$ |
| 60 | ' |
| 61 | |
| 62 | # =======================8< end of configuration >8======================= |
| 63 | |
| 64 | set -eu |
| 65 | |
| 66 | readonly FullTargetPath="${StateDir}/${TargetShortFile}" |
| 67 | readonly WorkingFile="${FullTargetPath}.$$" |
| 68 | |
| 69 | progname="$(basename "$0")" |
| 70 | note() { printf >&2 '%s: %s\n' "$progname" "$*"; } |
| 71 | die() { note "$@"; exit 1; } |
| 72 | |
| 73 | # guard against stomping on file-permissions |
| 74 | [ ".$(id -un)" = ".${RuntimeUser:?}" ] || \ |
| 75 | die "must be invoked as ${RuntimeUser}" |
| 76 | |
| 77 | fetch_candidate() { |
| 78 | curl --user-agent "$CurlUserAgent" -fSs -o "${WorkingFile}" "${URL}" |
| 79 | } |
| 80 | |
| 81 | case $(uname -s) in |
| 82 | *BSD|Darwin) |
| 83 | size_of() { stat -f %z "$1"; } |
| 84 | ;; |
| 85 | Linux) |
| 86 | size_of() { stat -c %s "$1"; } |
| 87 | ;; |
| 88 | *) |
| 89 | # why do we live in a world where Perl is the safe portable solution |
| 90 | # to getting the size of a file? |
| 91 | size_of() { perl -le 'print((stat($ARGV[0]))[7])' -- "$1"; } |
| 92 | ;; |
| 93 | esac |
| 94 | |
| 95 | sanity_check_candidate() { |
| 96 | local new_size prev_size re |
| 97 | new_size="$(size_of "$WorkingFile")" |
| 98 | |
| 99 | for re in $MustExistRegexps; do |
| 100 | grep -qs "$re" -- "$WorkingFile" || \ |
| 101 | die "regexp $re not found in $WorkingFile" |
| 102 | done |
| 103 | |
| 104 | if ! prev_size="$(size_of "$FullTargetPath")"; then |
| 105 | note "missing previous file, can't size-compare: $FullTargetPath" |
| 106 | # We're sane by definition, probably initial fetch, and the |
| 107 | # stat failure and this note will be printed. That's fine; if |
| 108 | # a cron invocation is missing the file then something has gone |
| 109 | # badly wrong. |
| 110 | return 0 |
| 111 | fi |
| 112 | local ratio |
| 113 | ratio=$(expr $new_size \* 100 / $prev_size) |
| 114 | if [ $ratio -lt $MinNewSizeRation ]; then |
| 115 | die "New $TargetShortFile candidate only ${ratio}% size of old; $new_size vs $prev_size" |
| 116 | fi |
| 117 | } |
| 118 | |
| 119 | if [ "${1:-.}" = "cron" ]; then |
| 120 | shift |
| 121 | # Don't pull on-the-minute, wait for off-cycle-peak |
| 122 | sleep $(( ($(dd if=/dev/urandom bs=1 count=1 2>/dev/null | hexdump -e '1/1 "%u"') % 40) + 10)) |
| 123 | fi |
| 124 | |
| 125 | umask 022 |
| 126 | fetch_candidate |
| 127 | sanity_check_candidate |
| 128 | mv -- "$WorkingFile" "$FullTargetPath" |