env: Add support for access control to .flags

Add support for read-only, write-once, and change-default.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

tools/env/fw_env.c

@@ -181,6 +181,32 @@ char *fw_getenv (char *name)
 	return NULL;
 }
 
+/*
+ * Search the default environment for a variable.
+ * Return the value, if found, or NULL, if not found.
+ */
+char *fw_getdefenv(char *name)
+{
+	char *env, *nxt;
+
+	for (env = default_environment; *env; env = nxt + 1) {
+		char *val;
+
+		for (nxt = env; *nxt; ++nxt) {
+			if (nxt >= &default_environment[ENV_SIZE]) {
+				fprintf(stderr, "## Error: "
+					"default environment not terminated\n");
+				return NULL;
+			}
+		}
+		val = envmatch(name, env);
+		if (!val)
+			continue;
+		return val;
+	}
+	return NULL;
+}
+
 /*
  * Print the current definition of one, or more, or all
  * environment variables
@@ -282,6 +308,7 @@ int fw_env_write(char *name, char *value)
 	int len;
 	char *env, *nxt;
 	char *oldval = NULL;
+	int deleting, creating, overwriting;
 
 	/*
 	 * search if variable with this name already exists
@@ -299,10 +326,49 @@ int fw_env_write(char *name, char *value)
 			break;
 	}
 
-	/*
-	 * Delete any existing definition
-	 */
-	if (oldval) {
+	deleting = (oldval && !(value && strlen(value)));
+	creating = (!oldval && (value && strlen(value)));
+	overwriting = (oldval && (value && strlen(value)));
+
+	/* check for permission */
+	if (deleting) {
+		if (env_flags_validate_varaccess(name,
+		    ENV_FLAGS_VARACCESS_PREVENT_DELETE)) {
+			printf("Can't delete \"%s\"\n", name);
+			errno = EROFS;
+			return -1;
+		}
+	} else if (overwriting) {
+		if (env_flags_validate_varaccess(name,
+		    ENV_FLAGS_VARACCESS_PREVENT_OVERWR)) {
+			printf("Can't overwrite \"%s\"\n", name);
+			errno = EROFS;
+			return -1;
+		} else if (env_flags_validate_varaccess(name,
+		    ENV_FLAGS_VARACCESS_PREVENT_NONDEF_OVERWR)) {
+			const char *defval = fw_getdefenv(name);
+
+			if (defval == NULL)
+				defval = "";
+			if (strcmp(oldval, defval)
+			    != 0) {
+				printf("Can't overwrite \"%s\"\n", name);
+				errno = EROFS;
+				return -1;
+			}
+		}
+	} else if (creating) {
+		if (env_flags_validate_varaccess(name,
+		    ENV_FLAGS_VARACCESS_PREVENT_CREATE)) {
+			printf("Can't create \"%s\"\n", name);
+			errno = EROFS;
+			return -1;
+		}
+	} else
+		/* Nothing to do */
+		return 0;
+
+	if (deleting || overwriting) {
 #ifndef CONFIG_ENV_OVERWRITE
 		/*
 		 * Ethernet Address and serial# can be set only once