[pacman-dev] [PATCH 2/2] pacman-key: make sure we actually use the Web of Trust, which GnuPG doesn't.

[Eli Schwartz]

By default, the latest versions of GnuPG disable the Web of Trust and
refuse to import signatures from public keyservers. This is to prevent
denial of service attacks, because refusing to import signatures only if
the key size is too big, is apparently too silly to consider.

Either way, pacman needs the WoT. If pacman imports a key at all, it
means everything failed and we are in fallback mode, trying to overcome
a shortcoming in the availability of keys in the keyring package.
(This commonly means the user needs to acquire a new key during the same
transaction that updates archlinux-keyring.)
In order for that new key to be usable, it *must* also import signatures
from the Master Keys.

I don't give credence to this supposed DoS, since the worst case
scenario is nothing happening and needing to CTRL+C in order to exit the
program. In the case of pacman, this is better than being unable to
install anything at all (which is gnupg doing a much more harmful DoS to
pacman), and in the already unusual case where something like
--refresh-keys is being used directly instead of depending on the
keyring package itself, gnupg supports WKD out of the box and will
prefer that for people whose keys are marketed as being non-DOSable.

Signed-off-by: Eli Schwartz <eschwartz at archlinux.org>
---

I've been sitting on this for a bit, but this does seem to be the best
way to implement a reversion to the old method. Feel free to bikeshed
about version checks in pacman-key!

This is independent of the WKD patchset, and works for people without
@archlinux.org uids, or more generally for pacman downstreams that don't
have a WKD infrastructure.

In the long run, I expect the keyservers to implement less insane DoS
mitigations, for example, an evolution of hagrid that supports mutually
signed keys. I don't know if I should hold my breath waiting for gnupg
to get proper error checking, though!
Once proper mitigations exist, we'd need to disable the builtin default
self-sigs-only,import-clean anyway, assuming gnupg itself didn't roll
back these settings. 

 scripts/pacman-key.sh.in | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/scripts/pacman-key.sh.in b/scripts/pacman-key.sh.in
index c3b02850..d6ba0e3b 100644
--- a/scripts/pacman-key.sh.in
+++ b/scripts/pacman-key.sh.in
@@ -210,6 +210,11 @@ initialize() {
 	add_gpg_conf_option "$conffile" 'lock-never'
 	add_gpg_conf_option "$conffile" 'keyserver-options' 'timeout=10'
 
+	local gpg_ver=$(gpg --version | awk '{print $3; exit}')
+	if (( $(vercmp "$gpg_ver" 2.2.17) >= 0 )); then
+		add_gpg_conf_option "$conffile" 'keyserver-options' 'no-self-sigs-only,no-import-clean'
+	fi
+
 	# gpg-agent.conf
 	agent_conffile="${PACMAN_KEYRING_DIR}/gpg-agent.conf"
 	[[ -f $agent_conffile ]] || touch "$agent_conffile"
-- 
2.22.0