wpa_supplicant: allow both imperative and declarative networks

For a while now it's possible to specify an additional config file in
`wpa_supplicant`[1]. In contrast to the file specified via `-c` this was
supposed to be used for immutable settings and not e.g. additional
networks.

However I'm a little bit unhappy about the fact that one has to choose
between a fully imperative setup and a fully declarative one where the
one would have to write credentials for e.g. WPA2-enterprise networks
into the store.

The primary problem with the current state of `wpa_supplicant` is that
if the `SAVE_CONFIG` command is invoked (e.g. via `wpa_cli`), all known
networks will be written to `/etc/wpa_supplicant.conf` and thus all
declarative networks would get out of sync with the declarative
settings.

To work around this, I had to change the following things:

* The `networking.wireless`-module now uses `-I` for declarative config,
  so the user-controlled mode can be used along with the
  `networks`-option.

* I added an `ro`-field to the `ssid`-struct in the
  `wpa_supplicant`-sources. This will be set to `1` for each network
  specified in the config passed via `-I`.

  Whenever config is written to the disk, those networks will be
  skipped, so changes to declarative networks are only temporary.

[1] https://w1.fi/cgit/hostap/commit/wpa_supplicant?id=e6304cad47251e88d073553042f1ea7805a858d1

nixos/modules/services/networking/wpa_supplicant.nix

@@ -236,7 +236,7 @@ in {
         if [ -f /etc/wpa_supplicant.conf -a "/etc/wpa_supplicant.conf" != "${configFile}" ]
         then echo >&2 "<3>/etc/wpa_supplicant.conf present but ignored. Generated ${configFile} is used instead."
         fi
-        iface_args="-s -u -D${cfg.driver} -c ${configFile}"
+        iface_args="-s -u -D${cfg.driver} -c /etc/wpa_supplicant.conf -I ${configFile}"
         ${if ifaces == [] then ''
           for i in $(cd /sys/class/net && echo *); do
             DEVTYPE=

pkgs/os-specific/linux/wpa_supplicant/0001-Implement-read-only-mode-for-ssids.patch

@@ -0,0 +1,130 @@
+From 99ae610f0ae3608a12c864caedf396f14e68327d Mon Sep 17 00:00:00 2001
+From: Maximilian Bosch <maximilian@mbosch.me>
+Date: Fri, 19 Feb 2021 19:44:21 +0100
+Subject: [PATCH] Implement read-only mode for ssids
+
+With this change it's possible to define `network=`-sections in a second
+config file specified via `-I` without having changes written to
+`/etc/wpa_supplicant.conf`.
+
+This is helpful on e.g. NixOS to allow both declarative (i.e. read-only)
+and imperative (i.e. mutable) networks.
+---
+ wpa_supplicant/config.h         | 2 +-
+ wpa_supplicant/config_file.c    | 5 +++--
+ wpa_supplicant/config_none.c    | 2 +-
+ wpa_supplicant/config_ssid.h    | 2 ++
+ wpa_supplicant/wpa_supplicant.c | 8 ++++----
+ 5 files changed, 11 insertions(+), 8 deletions(-)
+
+diff --git a/wpa_supplicant/config.h b/wpa_supplicant/config.h
+index 6a297ecfe..adaf4d398 100644
+--- a/wpa_supplicant/config.h
++++ b/wpa_supplicant/config.h
+@@ -1614,7 +1614,7 @@ const char * wpa_config_get_global_field_name(unsigned int i, int *no_var);
+  *
+  * Each configuration backend needs to implement this function.
+  */
+-struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp);
++struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp, int ro);
+ 
+ /**
+  * wpa_config_write - Write or update configuration data
+diff --git a/wpa_supplicant/config_file.c b/wpa_supplicant/config_file.c
+index 77c326df5..d5ed051b9 100644
+--- a/wpa_supplicant/config_file.c
++++ b/wpa_supplicant/config_file.c
+@@ -373,7 +373,7 @@ static int wpa_config_process_blob(struct wpa_config *config, FILE *f,
+ #endif /* CONFIG_NO_CONFIG_BLOBS */
+ 
+ 
+-struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp)
++struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp, int ro)
+ {
+ 	FILE *f;
+ 	char buf[512], *pos;
+@@ -415,6 +415,7 @@ struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp)
+ 	while (wpa_config_get_line(buf, sizeof(buf), f, &line, &pos)) {
+ 		if (os_strcmp(pos, "network={") == 0) {
+ 			ssid = wpa_config_read_network(f, &line, id++);
++			ssid->ro = ro;
+ 			if (ssid == NULL) {
+ 				wpa_printf(MSG_ERROR, "Line %d: failed to "
+ 					   "parse network block.", line);
+@@ -1591,7 +1592,7 @@ int wpa_config_write(const char *name, struct wpa_config *config)
+ 	}
+ 
+ 	for (ssid = config->ssid; ssid; ssid = ssid->next) {
+-		if (ssid->key_mgmt == WPA_KEY_MGMT_WPS || ssid->temporary)
++		if (ssid->key_mgmt == WPA_KEY_MGMT_WPS || ssid->temporary || ssid->ro == 1)
+ 			continue; /* do not save temporary networks */
+ 		if (wpa_key_mgmt_wpa_psk(ssid->key_mgmt) && !ssid->psk_set &&
+ 		    !ssid->passphrase)
+diff --git a/wpa_supplicant/config_none.c b/wpa_supplicant/config_none.c
+index 2aac28fa3..02191b425 100644
+--- a/wpa_supplicant/config_none.c
++++ b/wpa_supplicant/config_none.c
+@@ -17,7 +17,7 @@
+ #include "base64.h"
+ 
+ 
+-struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp)
++struct wpa_config * wpa_config_read(const char *name, struct wpa_config *cfgp, int ro)
+ {
+ 	struct wpa_config *config;
+ 
+diff --git a/wpa_supplicant/config_ssid.h b/wpa_supplicant/config_ssid.h
+index d5c5c00a9..fd80c079c 100644
+--- a/wpa_supplicant/config_ssid.h
++++ b/wpa_supplicant/config_ssid.h
+@@ -93,6 +93,8 @@ struct wpa_ssid {
+ 	 */
+ 	int id;
+ 
++	int ro;
++
+ 	/**
+ 	 * priority - Priority group
+ 	 *
+diff --git a/wpa_supplicant/wpa_supplicant.c b/wpa_supplicant/wpa_supplicant.c
+index 911d79d17..cb0cb99b1 100644
+--- a/wpa_supplicant/wpa_supplicant.c
++++ b/wpa_supplicant/wpa_supplicant.c
+@@ -1052,14 +1052,14 @@ int wpa_supplicant_reload_configuration(struct wpa_supplicant *wpa_s)
+ 
+ 	if (wpa_s->confname == NULL)
+ 		return -1;
+-	conf = wpa_config_read(wpa_s->confname, NULL);
++	conf = wpa_config_read(wpa_s->confname, NULL, 0);
+ 	if (conf == NULL) {
+ 		wpa_msg(wpa_s, MSG_ERROR, "Failed to parse the configuration "
+ 			"file '%s' - exiting", wpa_s->confname);
+ 		return -1;
+ 	}
+ 	if (wpa_s->confanother &&
+-	    !wpa_config_read(wpa_s->confanother, conf)) {
++	    !wpa_config_read(wpa_s->confanother, conf, 1)) {
+ 		wpa_msg(wpa_s, MSG_ERROR,
+ 			"Failed to parse the configuration file '%s' - exiting",
+ 			wpa_s->confanother);
+@@ -5638,7 +5638,7 @@ static int wpa_supplicant_init_iface(struct wpa_supplicant *wpa_s,
+ #else /* CONFIG_BACKEND_FILE */
+ 		wpa_s->confname = os_strdup(iface->confname);
+ #endif /* CONFIG_BACKEND_FILE */
+-		wpa_s->conf = wpa_config_read(wpa_s->confname, NULL);
++		wpa_s->conf = wpa_config_read(wpa_s->confname, NULL, 0);
+ 		if (wpa_s->conf == NULL) {
+ 			wpa_printf(MSG_ERROR, "Failed to read or parse "
+ 				   "configuration '%s'.", wpa_s->confname);
+@@ -5646,7 +5646,7 @@ static int wpa_supplicant_init_iface(struct wpa_supplicant *wpa_s,
+ 		}
+ 		wpa_s->confanother = os_rel2abs_path(iface->confanother);
+ 		if (wpa_s->confanother &&
+-		    !wpa_config_read(wpa_s->confanother, wpa_s->conf)) {
++		    !wpa_config_read(wpa_s->confanother, wpa_s->conf, 1)) {
+ 			wpa_printf(MSG_ERROR,
+ 				   "Failed to read or parse configuration '%s'.",
+ 				   wpa_s->confanother);
+-- 
+2.29.2
+

pkgs/os-specific/linux/wpa_supplicant/default.nix

@@ -43,6 +43,8 @@ stdenv.mkDerivation rec {
       url = "https://w1.fi/cgit/hostap/patch/?id=a0541334a6394f8237a4393b7372693cd7e96f15";
       sha256 = "1gbhlz41x1ar1hppnb76pqxj6vimiypy7c4kq6h658637s4am3xg";
     })
+    # Allow read-only networks
+    ./0001-Implement-read-only-mode-for-ssids.patch
   ];
 
   # TODO: Patch epoll so that the dbus actually responds