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64 lines
2.3 KiB
Bash
64 lines
2.3 KiB
Bash
#!/bin/sh
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# Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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# Use of this source code is governed by a BSD-style
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# license that can be found in the LICENSE file.
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#
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# This script is a workaround for a vpn-unfriendly behavior of the
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# original resolvconf by Thomas Hood. Unlike the `openresolv`
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# implementation (whose binary is also called resolvconf,
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# confusingly), the original resolvconf lacks a way to specify
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# "exclusive mode" for a provider configuration. In practice, this
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# means that if Tailscale wants to install a DNS configuration, that
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# config will get "blended" with the configs from other sources,
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# rather than override those other sources.
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#
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# This script gets installed at /etc/resolvconf/update-libc.d, which
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# is a directory of hook scripts that get run after resolvconf's libc
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# helper has finished rewriting /etc/resolv.conf. It's meant to notify
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# consumers of resolv.conf of a new configuration.
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#
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# Instead, we use that hook mechanism to reach into resolvconf's
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# stuff, and rewrite the libc-generated resolv.conf to exclusively
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# contain Tailscale's configuration - effectively implementing
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# exclusive mode ourselves in post-production.
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set -e
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if [ -n "$TAILSCALE_RESOLVCONF_HOOK_LOOP" ]; then
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# Hook script being invoked by itself, skip.
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exit 0
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fi
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if [ ! -f tun-tailscale.inet ]; then
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# Tailscale isn't trying to manage DNS, do nothing.
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exit 0
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fi
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if ! grep resolvconf /etc/resolv.conf >/dev/null; then
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# resolvconf isn't managing /etc/resolv.conf, do nothing.
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exit 0
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fi
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# Write out a modified /etc/resolv.conf containing just our config.
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(
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if [ -f /etc/resolvconf/resolv.conf.d/head ]; then
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cat /etc/resolvconf/resolv.conf.d/head
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fi
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echo "# Tailscale workaround applied to set exclusive DNS configuration."
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cat tun-tailscale.inet
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if [ -f /etc/resolvconf/resolv.conf.d/base ]; then
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# Keep options and sortlist, discard other base things since
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# they're the things we're trying to override.
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grep -e 'sortlist ' -e 'options ' /etc/resolvconf/resolv.conf.d/base || true
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fi
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if [ -f /etc/resolvconf/resolv.conf.d/tail ]; then
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cat /etc/resolvconf/resolv.conf.d/tail
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fi
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) >/etc/resolv.conf
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if [ -d /etc/resolvconf/update-libc.d ] ; then
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# Re-notify libc watchers that we've changed resolv.conf again.
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export TAILSCALE_RESOLVCONF_HOOK_LOOP=1
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exec run-parts /etc/resolvconf/update-libc.d
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fi
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