fix macOS dns-updown handling of parallel full redirects

The script didn't handle scenarios well where two or more parallel VPN
connections want to replace the default DNS server. The DNS configuration
has a chance to get broken by the connections going down in a different
order than they came up in.

Disallowing all but the first connection to modify the default DNS server
will effectively prevent this issue. While it may break DNS for the
latter connections, it is the best we can do without knowing specifics
about the configurations.

Change-Id: I7b413578a8fc0c65fca26f72b901a9f7bc34b137
Signed-off-by: Heiko Hund <heiko@ist.eigentlich.net>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Message-Id: <20250626091959.23505-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg31988.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/distro/dns-scripts/macos-dns-updown.sh b/distro/dns-scripts/macos-dns-updown.sh
index 89d688211c633d26d6199a4c77447820d1abc23d..c15abaaa7670f112a5d00b42ea08a272d56c519f 100644 (file)
--- a/distro/dns-scripts/macos-dns-updown.sh
+++ b/distro/dns-scripts/macos-dns-updown.sh
@@ -30,6 +30,7 @@
 
 itf_dns_key="State:/Network/Service/openvpn-${dev}/DNS"
 dns_backup_key="State:/Network/Service/openvpn-${dev}/DnsBackup"
+dns_backup_key_pattern="State:/Network/Service/openvpn-.*/DnsBackup"
 
 function primary_dns_key {
     local uuid=$(echo "show State:/Network/Global/IPv4" | /usr/sbin/scutil | grep "PrimaryService" | cut -d: -f2 | xargs)
@@ -166,6 +167,11 @@ function set_dns {
         echo -e "${cmds}" | /usr/sbin/scutil
         set_search_domains "$search_domains"
     else
+        echo list ${dns_backup_key_pattern} | /usr/sbin/scutil | grep -q 'no key' || {
+            echo "setting DNS failed, already redirecting to another tunnel"
+            exit 1
+        }
+
         local cmds=""
         cmds+="get $(primary_dns_key)\n"
         cmds+="set ${dns_backup_key}\n"
@@ -200,6 +206,9 @@ function unset_dns {
         echo "remove ${itf_dns_key}" | /usr/sbin/scutil
         unset_search_domains "$search_domains"
     else
+        # Do not unset if this tunnel did not set/backup DNS before
+        echo list ${dns_backup_key} | /usr/sbin/scutil | grep -qv 'no key' || return
+
         local cmds=""
         cmds+="get ${dns_backup_key}\n"
         cmds+="set $(primary_dns_key)\n"