Fix DNS resolution in initramfs (#367)

Add DNS servers to /etc/resolv.conf after interfaces are setup via configure_networking:
* create /etc/resolv.conf from network infos of all configured interfaces
* include libnss_dns.so + libnss_files.so in initramfs
* copy libs into initrd required for DNS resolution

src/initramfs-tools/hooks/clevis.in

@@ -95,3 +95,11 @@ bash_bin=$(find_binary "bash")
 copy_exec "${curl_bin}" || die 2 "Unable to copy ${curl_bin} to initrd image"
 copy_exec "${awk_bin}" || die 2 "Unable to copy ${awk_bin} to initrd image"
 copy_exec "${bash_bin}" || die 2 "Unable to copy ${bash_bin} to initrd image"
+
+# Copy latest versions of shared objects needed for DNS resolution
+for so in $(ldconfig -p | sed -nr 's/^\s*libnss_files\.so\.[0-9]+\s.*=>\s*//p'); do
+  copy_exec "${so}"
+done
+for so in $(ldconfig -p | sed -nr 's/^\s*libnss_dns\.so\.[0-9]+\s.*=>\s*//p'); do
+  copy_exec "${so}"
+done

src/initramfs-tools/scripts/local-top/clevis.in

@@ -263,6 +263,23 @@ do_configure_networking() {
             echo "clevis: Warning: multiple network interfaces available but no ip= parameter provided."
         fi
         configure_networking
+
+        # Add DNS servers from configure_networking to /etc/resolv.conf
+        if [ ! -e /etc/resolv.conf ]; then
+            touch /etc/resolv.conf
+            for intf in /run/net-*.conf; do
+                . "${intf}"
+                if [ ! -z "${IPV4DNS0}" ] && [ "${IPV4DNS0}" != "0.0.0.0" ]; then
+                    echo nameserver "${IPV4DNS0}" >> /etc/resolv.conf
+                fi
+                if [ ! -z "${IPV4DNS1}" ] && [ "${IPV4DNS1}" != "0.0.0.0" ]; then
+                    echo nameserver "${IPV4DNS1}" >> /etc/resolv.conf
+                fi
+                if [ ! -z "${IPV6DNS0}" ]; then
+                    echo nameserver "${IPV6DNS0}" >> /etc/resolv.conf
+                fi
+            done
+        fi
     fi
 }