From 462b02de4107845ab235e1668f78a43a31eb11fc Mon Sep 17 00:00:00 2001
From: Ondrej Holy <oholy@redhat.com>
Date: Wed, 14 Jan 2026 13:38:42 +0100
Subject: [PATCH] [core,tcp] Fix PreferIPv6OverIPv4 fallback to IPv4 addresses

Backport of commit 0bdd8da0993231216a7bb4d5e6e33e47d817a944.

Co-Authored-By: Claude <noreply@anthropic.com>
---
 libfreerdp/core/tcp.c | 61 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 10 deletions(-)

diff --git a/libfreerdp/core/tcp.c b/libfreerdp/core/tcp.c
index 8a731f117..3cf24c160 100644
--- a/libfreerdp/core/tcp.c
+++ b/libfreerdp/core/tcp.c
@@ -1064,6 +1064,53 @@ static BOOL freerdp_tcp_set_keep_alive_mode(const rdpSettings* settings, int soc
 	return TRUE;
 }
 
+static struct addrinfo* reorder_addrinfo_by_preference(rdpContext* context, struct addrinfo* addr)
+{
+	WINPR_ASSERT(context);
+	WINPR_ASSERT(addr);
+
+	const BOOL preferIPv6 =
+	    freerdp_settings_get_bool(context->settings, FreeRDP_PreferIPv6OverIPv4);
+	if (!preferIPv6)
+		return addr;
+
+	struct addrinfo* ipv6Head = NULL;
+	struct addrinfo* ipv6Tail = NULL;
+	struct addrinfo* otherHead = NULL;
+	struct addrinfo* otherTail = NULL;
+
+	/* Partition the list into IPv6 and other addresses */
+	while (addr)
+	{
+		struct addrinfo* next = addr->ai_next;
+		addr->ai_next = NULL;
+
+		if (addr->ai_family == AF_INET6)
+		{
+			if (!ipv6Head)
+				ipv6Head = addr;
+			else
+				ipv6Tail->ai_next = addr;
+			ipv6Tail = addr;
+		}
+		else
+		{
+			if (!otherHead)
+				otherHead = addr;
+			else
+				otherTail->ai_next = addr;
+			otherTail = addr;
+		}
+		addr = next;
+	}
+
+	/* Concatenate the lists */
+	if (ipv6Tail)
+		ipv6Tail->ai_next = otherHead;
+
+	return ipv6Head ? ipv6Head : otherHead;
+}
+
 static int get_next_addrinfo(rdpContext* context, struct addrinfo* input, struct addrinfo** result,
                              UINT32 errorCode)
 {
@@ -1074,14 +1121,6 @@ static int get_next_addrinfo(rdpContext* context, struct addrinfo* input, struct
 	if (!addr)
 		goto fail;
 
-	if (freerdp_settings_get_bool(context->settings, FreeRDP_PreferIPv6OverIPv4))
-	{
-		while (addr && (addr->ai_family != AF_INET6))
-			addr = addr->ai_next;
-		if (!addr)
-			addr = input;
-	}
-
 	*result = addr;
 	return 0;
 
@@ -1161,9 +1200,11 @@ int freerdp_tcp_connect(rdpContext* context, rdpSettings* settings, const char*
 			freerdp_set_last_error_log(context, 0);
 
 			/*
-			 * If PreferIPv6OverIPv4 = TRUE we force to IPv6 if there
-			 * is such an address available, but fall back to first if not found
+			 * If PreferIPv6OverIPv4 = TRUE we reorder addresses by preference:
+			 * IPv6 addresses come first, then other addresses.
 			 */
+			result = reorder_addrinfo_by_preference(context, result);
+
 			const int rc =
 			    get_next_addrinfo(context, result, &addr, FREERDP_ERROR_DNS_NAME_NOT_FOUND);
 			if (rc < 0)
-- 
2.52.0