[03/11] env: add support for whitelisting variables from secondary environments

diff --git a/env/Kconfig b/env/Kconfig
index 1952463..d57594d 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -438,4 +438,21 @@  config ENV_UBI_VOLUME
 
 endif
 
+config ENV_VAR_WHITELIST
+	bool "Enable overriding some variables from secondary environments"
+	help
+	  This allows overriding some variables from secondary environments.
+	  After the first valid environment is loaded, a secondary environment
+	  is pre-loaded and its variables that are present in the whitelist will
+	  be added to the current environment or will override existing
+	  variables.
+
+config ENV_VAR_WHITELIST_LIST
+	depends on ENV_VAR_WHITELIST
+	string "Whitelist of variables from secondary environments"
+	help
+	  This defines the variables that are allowed to be overriden by
+	  ones from secondary environments.
+	  This is a list of environment variables that are space-separated.
+
 endmenu
diff --git a/env/common.c b/env/common.c
index 9d97541..00c454d 100644
--- a/env/common.c
+++ b/env/common.c
@@ -177,8 +177,15 @@  int env_import(const char *buf, int check)
 		return ret;
 	}
 
+#ifdef CONFIG_ENV_VAR_WHITELIST
+	if (himport_r(&env_htab, (char *)ep->data, ENV_SIZE, '\0',
+		      whitelisting ? H_NOCLEAR : 0, 0,
+		      whitelisting ? whitelist_nvars : 0,
+		      whitelisting ? whitelist : NULL, whitelisting)) {
+#else
 	if (himport_r(&env_htab, (char *)ep->data, ENV_SIZE, '\0', 0, 0,
 			0, NULL, false)) {
+#endif
 		gd->flags |= GD_FLG_ENV_READY;
 		return 1;
 	}
diff --git a/env/env.c b/env/env.c
index 5e70ddf..43a62b8 100644
--- a/env/env.c
+++ b/env/env.c
@@ -7,9 +7,18 @@ 
 
 #include <common.h>
 #include <environment.h>
+#ifdef CONFIG_ENV_VAR_WHITELIST
+# include <malloc.h>
+#endif
 
 DECLARE_GLOBAL_DATA_PTR;
 
+#ifdef CONFIG_ENV_VAR_WHITELIST
+char *const *whitelist;
+bool whitelisting;
+unsigned int whitelist_nvars;
+#endif
+
 static struct env_driver *_env_driver_lookup(enum env_location loc)
 {
 	struct env_driver *drv;
@@ -62,6 +71,31 @@  static enum env_location env_locations[] = {
 
 static enum env_location env_load_location;
 
+#ifdef CONFIG_ENV_VAR_WHITELIST
+void env_create_whitelist(void)
+{
+	char **wl_vars;
+	char *wl = strchr(CONFIG_ENV_VAR_WHITELIST_LIST, ' ');
+	unsigned int nvars = 0;
+
+	while(wl) {
+		nvars++;
+		wl = strchr(wl + 1, ' ');
+	}
+
+	whitelist_nvars = nvars + 1;
+
+	wl_vars = malloc(sizeof(char *) * (nvars + 1));
+
+	wl_vars[nvars] = strtok(CONFIG_ENV_VAR_WHITELIST_LIST, " ");
+	while (nvars) {
+		wl_vars[--nvars] = strtok(NULL, " ");
+	}
+
+	whitelist = wl_vars;
+}
+#endif
+
 __weak enum env_location env_get_location(enum env_operation op, int prio)
 {
 	switch (op) {
@@ -74,7 +108,11 @@  __weak enum env_location env_get_location(enum env_operation op, int prio)
 		return env_load_location = env_locations[prio];
 
 	case ENVO_SAVE:
+#ifdef CONFIG_ENV_VAR_WHITELIST
+		return env_locations[prio];
+#else
 		return env_load_location;
+#endif
 	}
 
 	return ENVL_UNKNOWN;
@@ -130,10 +168,12 @@  int env_load(void)
 {
 	struct env_driver *drv;
 	int prio;
+	int ret = 1;
+#ifdef CONFIG_ENV_VAR_WHITELIST
+	bool found = false;
+#endif
 
 	for (prio = 0; (drv = env_driver_lookup(ENVO_LOAD, prio)); prio++) {
-		int ret;
-
 		if (!drv->load)
 			continue;
 
@@ -144,16 +184,52 @@  int env_load(void)
 		ret = drv->load();
 		printf("%s\n", ret ? "Failed" : "OK");
 		if (!ret)
-			return 0;
+			break;
 	}
 
-	return -ENODEV;
+	if (ret)
+		return -ENODEV;
+
+#ifdef CONFIG_ENV_VAR_WHITELIST
+	env_create_whitelist();
+
+	whitelisting = true;
+	/* When whitelisting, env from prio x+n will override env from prio x */
+	for (prio++; prio < ARRAY_SIZE(env_locations); prio++) {
+		drv = env_driver_lookup(ENVO_LOAD, prio);
+		if (!drv)
+			continue;
+
+		if (!drv->load)
+			continue;
+
+		printf("Overriding env variables with ones from %s env...",
+		      __func__, drv->name);
+		ret = drv->load();
+		printf("%s\n", ret ? "Failed" : "OK");
+		if (!ret) {
+			found = true;
+			continue;
+		}
+	}
+
+out:
+	if (!found)
+		debug("%s: Couldn't find other valid env for whitelisting\n",
+		      __func__);
+
+	whitelisting = false;
+#endif
+	return 0;
 }
 
 int env_save(void)
 {
 	struct env_driver *drv;
 	int prio;
+#ifdef CONFIG_ENV_VAR_WHITELIST
+	bool saved = false;
+#endif
 
 	for (prio = 0; (drv = env_driver_lookup(ENVO_SAVE, prio)); prio++) {
 		int ret;
@@ -167,13 +243,23 @@  int env_save(void)
 		printf("Saving Environment to %s... ", drv->name);
 		ret = drv->save();
 		printf("%s\n", ret ? "Failed" : "OK");
+#ifdef CONFIG_ENV_VAR_WHITELIST
+		/* When whitelisting, we want to save to all media available */
+		if (!ret) {
+			saved = true;
+			continue;
+		}
+#else
 		if (!ret)
 			return 0;
-
-		debug("%s: Environment %s failed to save (err=%d)\n", __func__,
-		      drv->name, ret);
+#endif
 	}
 
+#ifdef CONFIG_ENV_VAR_WHITELIST
+	if (saved)
+		return 0;
+#endif
+
 	return -ENODEV;
 }
 
diff --git a/include/environment.h b/include/environment.h
index 7fa8b98..33e47ba 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -267,6 +267,12 @@  struct env_driver {
 	int (*init)(void);
 };
 
+#ifdef CONFIG_ENV_VAR_WHITELIST
+extern char *const *whitelist;
+extern unsigned int whitelist_nvars;
+extern bool whitelisting;
+#endif
+
 /* Declare a new environment location driver */
 #define U_BOOT_ENV_LOCATION(__name)					\
 	ll_entry_declare(struct env_driver, __name, env_driver)