sanebox: integrate with pasta (passt) for better net sandboxing

hosts/common/programs/assorted.nix

@@ -723,6 +723,8 @@ in
     # settings (electron app)
     obsidian.persist.byStore.plaintext = [ ".config/obsidian" ];
 
+    passt.sandbox.enable = false;  #< sandbox helper (netns specifically)
+
     parted.sandbox.method = "landlock";
     parted.sandbox.extraPaths = [
       "/dev"

modules/programs/default.nix

@@ -74,6 +74,10 @@ let
             vpn.name
           else
             sandbox.net;
+          netGateway = if sandbox.net == "vpn" then
+            vpn.addrV4
+          else
+            null;
           dns = if sandbox.net == "vpn" then
             vpn.dns
           else
@@ -429,9 +433,10 @@ let
         null
       else
         wrapPkg name config config.packageUnwrapped
-        ;
-      suggestedPrograms = lib.optionals (config.sandbox.method == "bwrap") [ "bubblewrap" ]
-        ++ lib.optionals (config.sandbox.method == "firejail") [ "firejail" ];
+      ;
+      suggestedPrograms = lib.optionals (config.sandbox.method == "bwrap") [
+        "bubblewrap" "passt"
+      ] ++ lib.optionals (config.sandbox.method == "firejail") [ "firejail" ];
       # declare a fs dependency for each secret, but don't specify how to populate it yet.
       #   can't populate it here because it varies per-user.
       # this gets the symlink into the sandbox, but not the actual secret.

modules/programs/make-sandbox-args.nix

@@ -7,6 +7,7 @@
 , capabilities ? []
 , dns ? null
 , netDev ? null
+, netGateway ? null
 , whitelistPwd ? false
 , extraConfig ? []
 }:
@@ -22,6 +23,9 @@ let
   netItems = lib.optionals (netDev != null) [
     "--sanebox-net-dev"
     netDev
+  ] ++ lib.optionals (netGateway != null) [
+    "--sanebox-net-gateway"
+    netGateway
   ] ++ lib.optionals (dns != null) (
     lib.flatten (builtins.map
       (addr: [ "--sanebox-dns" addr ])

pkgs/additional/sanebox/default.nix

@@ -1,6 +1,7 @@
 { lib, stdenv
 , bash
 , bubblewrap
+, passt
 , firejail
 , landlock-sandboxer
 , libcap
@@ -24,7 +25,8 @@ stdenv.mkDerivation {
       --replace-fail '@bwrap@' '${lib.getExe bubblewrap}' \
       --replace-fail '@firejail@' '${lib.getExe' firejail "firejail"}' \
       --replace-fail '@landlockSandboxer@' '${lib.getExe landlock-sandboxer}' \
-      --replace-fail '@capsh@' '${lib.getExe' libcap "capsh"}'
+      --replace-fail '@capsh@' '${lib.getExe' libcap "capsh"}' \
+      --replace-fail '@pasta@' '${lib.getExe' passt "pasta"}'
     runHook postBuild
   '';
 

pkgs/additional/sanebox/sanebox

@@ -6,6 +6,7 @@ FIREJAIL_FALLBACK='@firejail@'
 BWRAP_FALLBACK='@bwrap@'
 LANDLOCK_SANDBOXER_FALLBACK='@landlockSandboxer@'
 CAPSH_FALLBACK='@capsh@'
+PASTA_FALLBACK='@pasta@'
 
 
 ## EARLY DEBUG HOOKS
@@ -80,7 +81,10 @@ capabilities=()
 # - "all": as if all the above were specified
 keepNamespace=()
 # name of some network device to make available to the sandbox, if any.
+# or "all" to keep all devices available
 netDev=
+# IPv4 address of the default gateway associated with the bridged network device (usually that's just the VPN's IP addr)
+netGateway=
 # list of IP addresses to use for DNS servers inside the sandbox (firejail only)
 dns=()
 # list of `VAR=VALUE` environment variables to add to the sandboxed program's environment
@@ -121,6 +125,7 @@ usage() {
   echo '  --sanebox-firejail-arg <arg>'
   echo '  --sanebox-bwrap-arg <arg>'
   echo '  --sanebox-net-dev <iface>'
+  echo '  --sanebox-net-gateway <ip-address>'
   echo '  --sanebox-dns <server>'
   echo '  --sanebox-keep-namespace <cgroup|ipc|pid|uts|all>'
   echo '      do not unshare the provided linux namespace'
@@ -516,10 +521,14 @@ parseArgs() {
         netDev=$1
         shift
         ;;
-      (--sanebox-dns)
-        local dns=$1
+      (--sanebox-net-gateway)
+        netGateway=$1
         shift
-        dns+=("$dns")
+        ;;
+      (--sanebox-dns)
+        local dnsServer=$1
+        shift
+        dns+=("$dnsServer")
         ;;
       (--sanebox-keep-namespace)
         local namespace=$1
@@ -578,6 +587,9 @@ firejailIngestNetDev() {
   # firejail can then spawn a veth from this bridge and namespace it that way.
   firejailFlags+=("--net=br-$1")
 }
+firejailIngestNetGateway() {
+  debug "firejailIngestNetGateway: noop"
+}
 firejailIngestDns() {
   firejailFlags+=("--dns=$1")
 }
@@ -604,6 +616,9 @@ bwrapUnshareUts=(--unshare-uts)
 bwrapVirtualizeDev=(--dev /dev)
 bwrapVirtualizeProc=(--proc /proc)
 bwrapVirtualizeTmp=(--tmpfs /tmp)
+# args to invoke `pasta` (user-mode network stack) with
+bwrapPastaArgs=()
+bwrapNetSetup=
 
 bwrapSetup() {
   debug "bwrapSetup: noop"
@@ -652,8 +667,22 @@ bwrapIngestPath() {
   esac
 }
 bwrapIngestNetDev() {
-  debug "bwrapIngestNetDev: enabling full net access for '$1' because don't know how to restrict it more narrowly"
+  local dev=$1
   bwrapUnshareNet=()
+  case $dev in
+    (all)
+      ;;
+    (*)
+      bwrapPastaArgs+=(--outbound-if4 "$dev")
+      ;;
+  esac
+}
+bwrapIngestNetGateway() {
+  bwrapPastaArgs+=(--gateway "$1")
+}
+bwrapIngestDns() {
+  # NAT DNS requests to localhost to the VPN's DNS resolver
+  bwrapNetSetup="ip addr del 127.0.0.1/8 dev lo; iptables -A OUTPUT -t nat -p udp --dport 53 -m iprange --dst-range 127.0.0.1 -j DNAT --to-destination $1:53; $bwrapNetSetup"
 }
 bwrapIngestKeepNamespace() {
   case $1 in
@@ -693,6 +722,21 @@ bwrapGetCli() {
       "${bwrapFlags[@]}" --
     env "${portalEnv[@]}" "${cliArgs[@]}"
   )
+  if [ ${#bwrapPastaArgs} -ne 0 ]; then
+    # if [ -n "$bwrapNetSetup" ]; then
+      cliArgs=(
+        "/bin/sh" "-c"
+        "$bwrapNetSetup exec"' "$0" "$@"'
+        "${cliArgs[@]}"
+      )
+    # fi
+    locate _pasta "pasta" "$PASTA_FALLBACK"
+    cliArgs=(
+      "$_pasta" --ipv4-only -U none -T none --config-net
+        "${bwrapPastaArgs[@]}" --
+      "${cliArgs[@]}"
+    )
+  fi
 }
 
 
@@ -741,6 +785,12 @@ landlockIngestPath() {
 landlockIngestNetDev() {
   debug "landlockIngestNetDev: '$1': stubbed (landlock network is always unrestricted)"
 }
+landlockIngestNetGateway() {
+  debug "landlockIngestNetGateway: noop"
+}
+landlockIngestDns() {
+  debug "landlockIngestDns: noop"
+}
 landlockIngestKeepNamespace() {
   debug "landlockIngestKeepNamespace: noop"
 }
@@ -776,6 +826,12 @@ capshonlyIngestPath() {
 capshonlyIngestNetDev() {
   debug "capshonlyIngestNetDev: '$1': stubbed (capsh network is always unrestricted)"
 }
+capshonlyIngestNetGateway() {
+  debug "capshonlyIngestNetGateway: '$1': stubbed (capsh network is always unrestricted)"
+}
+capshonlyIngestDns() {
+  debug "capshonlyIngestDns: '$1': stubbed (capsh network is always unrestricted)"
+}
 capshonlyIngestKeepNamespace() {
   debug "capshonlyIngestKeepNamespace: noop"
 }
@@ -944,7 +1000,11 @@ ingestForBackend() {
   done
 
   if [ -n "$netDev" ]; then
-    "$method"IngestNetDev"$netDev"
+    "$method"IngestNetDev "$netDev"
+  fi
+
+  if [ -n "$netGateway" ]; then
+    "$method"IngestNetGateway "$netGateway"
   fi
 
   for addr in "${dns[@]}"; do