Rework trusted proxies (#5549)

* Rework trusted proxies
Fix https://github.com/FreshRSS/FreshRSS/issues/5502
Follow-up of https://github.com/FreshRSS/FreshRSS/pull/3226

New environment variable `TRUSTED_PROXY`: set to 0 to disable, or to a list of trusted IP ranges compatible with https://httpd.apache.org/docs/current/mod/mod_remoteip.html#remoteiptrustedproxy

New internal environment variable `CONN_REMOTE_ADDR` to remember the true IP address of the connection (e.g. last proxy), even when using mod_remoteip.

Current working setups should not observe any significant change.

* Minor whitespace

* Safer trusted sources during install
Rework of https://github.com/FreshRSS/FreshRSS/pull/5358
https://github.com/FreshRSS/FreshRSS/issues/5357

* Minor readme

1 files changed, 31 insertions, 9 deletions

diff --git a/lib/lib_rss.php b/lib/lib_rss.php
index ec00513e2..9d995c6d6 100644
--- a/lib/lib_rss.php
+++ b/lib/lib_rss.php
@@ -653,21 +653,43 @@ function checkCIDR(string $ip, string $range): bool {
 }
 
 /**
- * Check if the client is allowed to send unsafe headers
- * This uses the REMOTE_ADDR header to determine the sender’s IP
- * and the configuration option "trusted_sources" to get an array of the authorized ranges
- *
+ * Use CONN_REMOTE_ADDR (if available, to be robust even when using Apache mod_remoteip) or REMOTE_ADDR environment variable to determine the connection IP.
+ */
+function connectionRemoteAddress(): string {
+	$remoteIp = $_SERVER['CONN_REMOTE_ADDR'] ?? '';
+	if ($remoteIp == '') {
+		$remoteIp = $_SERVER['REMOTE_ADDR'] ?? '';
+	}
+	if ($remoteIp == 0) {
+		$remoteIp = '';
+	}
+	return $remoteIp;
+}
+
+/**
+ * Check if the client (e.g. last proxy) is allowed to send unsafe headers.
+ * This uses the `TRUSTED_PROXY` environment variable or the `trusted_sources` configuration option to get an array of the authorized ranges,
+ * The connection IP is obtained from the `CONN_REMOTE_ADDR` (if available, to be robust even when using Apache mod_remoteip) or `REMOTE_ADDR` environment variables.
  * @return bool, true if the sender’s IP is in one of the ranges defined in the configuration, else false
  */
 function checkTrustedIP(): bool {
 	if (FreshRSS_Context::$system_conf === null) {
 		return false;
 	}
-	if (!empty($_SERVER['REMOTE_ADDR'])) {
-		foreach (FreshRSS_Context::$system_conf->trusted_sources as $cidr) {
-			if (checkCIDR($_SERVER['REMOTE_ADDR'], $cidr)) {
-				return true;
-			}
+	$remoteIp = connectionRemoteAddress();
+	if ($remoteIp === '') {
+		return false;
+	}
+	$trusted = getenv('TRUSTED_PROXY');
+	if ($trusted != 0 && is_string($trusted)) {
+		$trusted = preg_split('/\s+/', $trusted, -1, PREG_SPLIT_NO_EMPTY);
+	}
+	if (empty($trusted)) {
+		$trusted = FreshRSS_Context::$system_conf->trusted_sources;
+	}
+	foreach (FreshRSS_Context::$system_conf->trusted_sources as $cidr) {
+		if (checkCIDR($remoteIp, $cidr)) {
+			return true;
 		}
 	}
 	return false;