path: root/local/require-signed-push

#!/bin/bash
# gentoo-infra: infra/githooks.git:local/require-signed-push

VERIFY_SIGS=$(git config --get gentoo.verify-signatures)
: "${VERIFY_SIGS:=gentoo-devs}"

# ----------------------------------------------------------------------
# standard stuff
silent_die() { exit 1; }
die() { echo "$@" >&2; silent_die; }
warn() { echo "$@" >&2; }

fail_signed_push() {
	warn "$@"
	warn "Your push was not signed with a known key."
	warn "You MUST use git push --signed with a known key."
	warn "Known keys are the subkeys of all primary keys in LDAP."
	warn "If you add a new (primary) key to LDAP, please ask Infra to sync gitolite."
	warn "If you modified your key and uploaded to keyservers, please wait 4 hours for sync (SKS pool is slow, keys.gentoo.org pool is faster)"
	warn "If you haven't done either of these things, please see https://wiki.gentoo.org/wiki/Project:Gentoo-keys/Generating_GLEP_63_based_OpenPGP_keys#Next_steps"
	warn "git-receive-pack variables:"
	for var in \
		GIT_PUSH_CERT \
		GIT_PUSH_CERT_KEY \
		GIT_PUSH_CERT_NONCE \
		GIT_PUSH_CERT_NONCE_SLOP \
		GIT_PUSH_CERT_NONCE_STATUS \
		GIT_PUSH_CERT_SIGNER \
		GIT_PUSH_CERT_STATUS \
		; do
			warn "$var='${!var}'"
	done
	if [ -n "${GIT_PUSH_CERT}" ]; then
		warn "A push-cert was found, and follows:"
		warn "====="
		git --no-pager show "$GIT_PUSH_CERT"
		warn "====="
	fi
	exit 1
}

log_git_push() {
	s=""
	for var in \
		GIT_PUSH_CERT \
		GIT_PUSH_CERT_KEY \
		GIT_PUSH_CERT_NONCE \
		GIT_PUSH_CERT_NONCE_SLOP \
		GIT_PUSH_CERT_NONCE_STATUS \
		GIT_PUSH_CERT_SIGNER \
		GIT_PUSH_CERT_STATUS \
		; do
			s="${s} $var='${!var}'"
	done
	logger -t require-signed-push -p info "require-signed-push${s}"
}

verify_pusher_clock() {
	RAW_CERT="$(git show --format='pushtime %ct%nct %ct%nat %at%n%B' "$GIT_PUSH_CERT")"
	# Example inputs
	# Good clock (58 seconds delay on PIN entry to smartcard):
	# -------
	# pushtime 1468598038
	# certificate version 0.1
	# pusher 0x250B7AFED6379D85! 1468597981 +0200
	# nonce 1468597981-660c323b3137c0798711
	# -------
	# Bad clock, ~5 mins slow:
	# -------
	# pushtime 1468596921
	# certificate version 0.1
	# pusher 94BFDF4484AD142F 1468596642 +0200
	# nonce 1468596917-ac5118c996e285ace24e
	# -------
	# Bad clock, ~5 mins fast
	# -------
	# pushtime 1468596921
	# certificate version 0.1
	# pusher 94BFDF4484AD142F 1468597242 +0200
	# nonce 1468596917-ac5118c996e285ace24e
	# -------

	# This is the time, according to server clock, that the server sent out to the user
	# also in GIT_PUSH_CERT_NONCE
	SERVER_NONCE_TIME="$(echo "$RAW_CERT" | awk '/^nonce /{sub("-.*","",$2); print $2}' )"
	# This is the time, according to USER clock, that the response was signed
	# We want the second to last field, because sometimes there are spaces!
	# pusher 94BFDF4484AD142F 1468596642 +0200
	# pusher Michael Palimaka <kensington@gentoo.org> 1468524562 +1000
	PUSHER_SIGN_TIME="$(echo "$RAW_CERT" | awk '/^pusher /{s=$(NF-1); print s}')"
	# This is the time, according to server clock, when the server got the response
	SERVER_PUSH_TIME="$(echo "$RAW_CERT" | awk '/^pushtime /{print $2}')"
	# But it might not be available...
	[[ -z "${SERVER_PUSH_TIME}" ]] && SERVER_PUSH_TIME=$(date +%s)

	[[ -z "$SERVER_NONCE_TIME" ]] && die "require-signed-push: Could not find push nonce"
	[[ -z "$PUSHER_SIGN_TIME" ]] && die "require-signed-push: Could not find pusher identity"

	# Timestamps:
	# T0: nonce generation time (server, trusted input)
	# T1: nonce signature START time (client, untrusted input!)
	# T2: signed-nonce receive time (server, trusted input)
	T0="$SERVER_NONCE_TIME"
	T1="$PUSHER_SIGN_TIME"
	T2="$SERVER_PUSH_TIME"
	# Durations:
	# T1-T0: how long it took the client to get the nonce and sign it (depends on untrusted input)
	# - will be negative if the client (T1) has a clock BEHIND of server (T0),
	#   e.g. client clock is "slow"
	#
	# T2-T0: how long the roundtrip took (only contains trusted inputs)
	# - will only be negative if the server clock jump backwards during the round-trip!
	#
	# T2-T1: how long it took the client to sign their timestamp & nonce and
	#        send it back (depends on untrusted input)
	# - will be negative if the client (T1) has a clock AHEAD of server (T2),
	#   e.g. clock is "fast"
	# - MAY contain delay from smartcards/tokens requiring interaction.
	DELTA_T1_T0=$(( T1 - T0 ))
	DELTA_T2_T0=$(( T2 - T0 ))
	DELTA_T2_T1=$(( T2 - T1 ))

	# Flip the signs, because we care about magnitude, not if they are fast or slow.
	[[ $DELTA_T1_T0 -lt 0 ]] && DELTA_T1_T0=$(( DELTA_T1_T0 * -1 ))
	[[ $DELTA_T2_T1 -lt 0 ]] && DELTA_T2_T1=$(( DELTA_T2_T1 * -1 ))
	# This one should never happen unless the server's clock has gone backwards during the round trip period.
	[[ $DELTA_T2_T0 -lt 0 ]] && die "Server clock moved backwards during process, please report to infra@ and retry!"

	CLOCK_DRIFT_LIMIT=5
	PUSH_LIMIT=60
	_die=0
	# Put the stricter check first, otherwise the weaker check will never be seen.
	if [[ $DELTA_T2_T0 -ge $PUSH_LIMIT ]]; then
		warn "Push roundtrip took too long (push-nonce): $DELTA_T2_T0 sec vs limit $PUSH_LIMIT"
		_die=1
	fi
	if [[ $DELTA_T1_T0 -ge $CLOCK_DRIFT_LIMIT ]]; then
		warn "Push certificate time is too skew (sign-nonce)."
		warn "It's possible your system clock is off by up to $DELTA_T1_T0 seconds vs limit $CLOCK_DRIFT_LIMIT"
		warn "Run NTP, pull & rebase your commits if needed, and push again."
		_die=1
	fi
	if [[ $_die -eq 1 ]]; then
		warn "---cut-here---"
		git show --format='pushtime %ct%nct %ct%nat %at%n%B' "$GIT_PUSH_CERT" 1>&2
		warn "---cut-here---"
		die "Time issues during git-push"
	fi
}

# ----------------------------------------------------------------------
# Send info to syslog for debugging
log_git_push

case ${VERIFY_SIGS} in
	gentoo-devs)
		if [[ ${GL_USER} != *@gentoo.org ]]; then
			echo "*** Pusher address is not @gentoo.org" >&2
			echo "    (it is ${GL_USER})" >&2
			echo "*** Please report this to infra" >&2
			exit 1
		fi

		# find key fingerprints in LDAP
		KEY_FPS=( $(ldapsearch "uid=${GL_USER%@gentoo.org}" -D '' -Z -LLL \
			gpgfingerprint -o ldif-wrap=no | \
			sed -n -e '/^gpgfingerprint: /{s/^.*://;s/ //g;p}') )
		# match signing key to the primary key
		PRIMARY_KEY=$(gpg --batch --with-colons --fingerprint "${GIT_PUSH_CERT_KEY}" \
			| sed -n -e '/^pub/{n;/^fpr/p}' | cut -d: -f10)
		if [[ -z ${PRIMARY_KEY} ]]; then
			fail_signed_push "Unable to identify primary key used for push"
		fi

		# primary key must match one of the fingerprints in LDAP
		if [[ " ${KEY_FPS[*]} " != *" ${PRIMARY_KEY} "* ]]; then
			fail_signed_push "Key used to sign the commit does not belong to ${GL_USER}"
		fi
		;;
	no)
		;;
	*)
		echo "Invalid value of gentoo.verify-signatures" >&2
		exit 1
esac

# Now validate
# see git-log(1) %G
# 2020/04/06: BGUXYREN
case $GIT_PUSH_CERT_STATUS in
	# Good
	G) ;;

	# signature itself has expired
	X) fail_signed_push "FAIL: push certificate signature is expired" ;;

	# key is expired, but the good signature is otherwise good
	Y) fail_signed_push "FAIL: key used for push certificate is expired" ;;

	# good signature made by an revoked key
	R) fail_signed_push "FAIL: key used for push certiticate is revoked" ;;

	# Bad
	B) fail_signed_push "FAIL: signature on push certificate is bad" ;;

	# Untrusted good
	U) ;; # TODO: deny this later
	#U) fail_signed_push "Good but untrusted signature" ;;

	# No signature
	N)
		if [ -z "$GIT_PUSH_CERT" ]; then
			fail_signed_push "FAIL: no push certificate found"
		else
			fail_signed_push "FAIL: push certificate with no signature" # wtf?
		fi
		;;

	# Can't verify -- usually means unknown key
	E)
		if [[ ${VERIFY_SIGS} != no ]]; then
			fail_signed_push "FAIL: Unknown OpenPGP key used for push certificate"
		fi
		;;

	# Future-proof
	*) fail_signed_push "FAIL: Unknown GIT_PUSH_CERT_STATUS" ;;

esac

# Check the clock on pusher system as well.
verify_pusher_clock

# All good now
exit 0