Fix auto_redirect fallback rule

docs/changelog.md

@@ -4,8 +4,16 @@ icon: material/alert-decagram
 
 #### 1.12.18
 
+* Add fallback routing rule for `auto_redirect` **1**
 * Fixes and improvements
 
+**1**:
+
+Adds a fallback iproute2 rule checked after system default rules (32766: main, 32767: default),
+ensuring traffic is routed to the sing-box table when no route is found in system tables.
+
+The rule index can be customized via `auto_redirect_iproute2_fallback_rule_index` (default: 32768).
+
 #### 1.12.17
 
 * Update uTLS to v1.8.2 **1**

docs/configuration/inbound/tun.md

@@ -2,6 +2,10 @@
 icon: material/new-box
 ---
 
+!!! quote "Changes in sing-box 1.12.18"
+
+    :material-plus: [auto_redirect_iproute2_fallback_rule_index](#auto_redirect_iproute2_fallback_rule_index)
+
 !!! quote "Changes in sing-box 1.12.0"
 
     :material-plus: [loopback_address](#loopback_address)
@@ -63,6 +67,7 @@ icon: material/new-box
   "auto_redirect": true,
   "auto_redirect_input_mark": "0x2023",
   "auto_redirect_output_mark": "0x2024",
+  "auto_redirect_iproute2_fallback_rule_index": 32768,
   "loopback_address": [
     "10.7.0.1"
   ],
@@ -278,6 +283,17 @@ Connection output mark used by `auto_redirect`.
 
 `0x2024` is used by default.
 
+#### auto_redirect_iproute2_fallback_rule_index
+
+!!! question "Since sing-box 1.12.18"
+
+Linux iproute2 fallback rule index generated by `auto_redirect`.
+
+This rule is checked after system default rules (32766: main, 32767: default),
+routing traffic to the sing-box table only when no route is found in system tables.
+
+`32768` is used by default.
+
 #### loopback_address
 
 !!! question "Since sing-box 1.12.0"

docs/configuration/inbound/tun.zh.md

@@ -2,6 +2,10 @@
 icon: material/new-box
 ---
 
+!!! quote "sing-box 1.12.18 中的更改"
+
+    :material-plus: [auto_redirect_iproute2_fallback_rule_index](#auto_redirect_iproute2_fallback_rule_index)
+
 !!! quote "sing-box 1.12.0 中的更改"
 
     :material-plus: [loopback_address](#loopback_address)
@@ -63,6 +67,7 @@ icon: material/new-box
   "auto_redirect": true,
   "auto_redirect_input_mark": "0x2023",
   "auto_redirect_output_mark": "0x2024",
+  "auto_redirect_iproute2_fallback_rule_index": 32768,
   "loopback_address": [
     "10.7.0.1"
   ],
@@ -277,6 +282,17 @@ tun 接口的 IPv6 前缀。
 
 默认使用 `0x2024`。
 
+#### auto_redirect_iproute2_fallback_rule_index
+
+!!! question "自 sing-box 1.12.18 起"
+
+`auto_redirect` 生成的 iproute2 回退规则索引。
+
+此规则在系统默认规则（32766: main，32767: default）之后检查，
+仅当系统路由表中未找到路由时才将流量路由到 sing-box 路由表。
+
+默认使用 `32768`。
+
 #### loopback_address
 
 !!! question "自 sing-box 1.12.0 起"

go.mod

@@ -33,7 +33,7 @@ require (
 	github.com/sagernet/sing-shadowsocks v0.2.8
 	github.com/sagernet/sing-shadowsocks2 v0.2.1
 	github.com/sagernet/sing-shadowtls v0.2.1-0.20250503051639-fcd445d33c11
-	github.com/sagernet/sing-tun v0.7.8
+	github.com/sagernet/sing-tun v0.7.9
 	github.com/sagernet/sing-vmess v0.2.7
 	github.com/sagernet/smux v1.5.50-sing-box-mod.1
 	github.com/sagernet/tailscale v1.80.3-sing-box-1.12-mod.2

go.sum

@@ -177,8 +177,8 @@ github.com/sagernet/sing-shadowsocks2 v0.2.1 h1:dWV9OXCeFPuYGHb6IRqlSptVnSzOelnq
 github.com/sagernet/sing-shadowsocks2 v0.2.1/go.mod h1:RnXS0lExcDAovvDeniJ4IKa2IuChrdipolPYWBv9hWQ=
 github.com/sagernet/sing-shadowtls v0.2.1-0.20250503051639-fcd445d33c11 h1:tK+75l64tm9WvEFrYRE1t0YxoFdWQqw/h7Uhzj0vJ+w=
 github.com/sagernet/sing-shadowtls v0.2.1-0.20250503051639-fcd445d33c11/go.mod h1:sWqKnGlMipCHaGsw1sTTlimyUpgzP4WP3pjhCsYt9oA=
-github.com/sagernet/sing-tun v0.7.8 h1:v9GYPL6V1ZiViqdoRYOy1MPE9b2E6SP0YYWCIGV5fGc=
+github.com/sagernet/sing-tun v0.7.9 h1:kcEFA0Xa+OVcrBGnlIl33+SrW/vuB3jtOw0HQNOSJzc=
-github.com/sagernet/sing-tun v0.7.8/go.mod h1:pUEjh9YHQ2gJT6Lk0TYDklh3WJy7lz+848vleGM3JPM=
+github.com/sagernet/sing-tun v0.7.9/go.mod h1:pUEjh9YHQ2gJT6Lk0TYDklh3WJy7lz+848vleGM3JPM=
 github.com/sagernet/sing-vmess v0.2.7 h1:2ee+9kO0xW5P4mfe6TYVWf9VtY8k1JhNysBqsiYj0sk=
 github.com/sagernet/sing-vmess v0.2.7/go.mod h1:5aYoOtYksAyS0NXDm0qKeTYW1yoE1bJVcv+XLcVoyJs=
 github.com/sagernet/smux v1.5.50-sing-box-mod.1 h1:XkJcivBC9V4wBjiGXIXZ229aZCU1hzcbp6kSkkyQ478=

option/tun.go

@@ -20,6 +20,7 @@ type TunInboundOptions struct {
 	AutoRedirect                          bool                             `json:"auto_redirect,omitempty"`
 	AutoRedirectInputMark                 FwMark                           `json:"auto_redirect_input_mark,omitempty"`
 	AutoRedirectOutputMark                FwMark                           `json:"auto_redirect_output_mark,omitempty"`
+	AutoRedirectIPRoute2FallbackRuleIndex int                              `json:"auto_redirect_iproute2_fallback_rule_index,omitempty"`
 	LoopbackAddress                       badoption.Listable[netip.Addr]   `json:"loopback_address,omitempty"`
 	StrictRoute                           bool                             `json:"strict_route,omitempty"`
 	RouteAddress                          badoption.Listable[netip.Prefix] `json:"route_address,omitempty"`

protocol/tun/inbound.go

@@ -174,6 +174,10 @@ func NewInbound(ctx context.Context, router adapter.Router, logger log.ContextLo
 	if ruleIndex == 0 {
 		ruleIndex = tun.DefaultIPRoute2RuleIndex
 	}
+	autoRedirectFallbackRuleIndex := options.AutoRedirectIPRoute2FallbackRuleIndex
+	if autoRedirectFallbackRuleIndex == 0 {
+		autoRedirectFallbackRuleIndex = tun.DefaultIPRoute2AutoRedirectFallbackRuleIndex
+	}
 	inputMark := uint32(options.AutoRedirectInputMark)
 	if inputMark == 0 {
 		inputMark = tun.DefaultAutoRedirectInputMark
@@ -200,6 +204,7 @@ func NewInbound(ctx context.Context, router adapter.Router, logger log.ContextLo
 			AutoRoute:                             options.AutoRoute,
 			IPRoute2TableIndex:                    tableIndex,
 			IPRoute2RuleIndex:                     ruleIndex,
+			IPRoute2AutoRedirectFallbackRuleIndex: autoRedirectFallbackRuleIndex,
 			AutoRedirectInputMark:                 inputMark,
 			AutoRedirectOutputMark:                outputMark,
 			Inet4LoopbackAddress:                  common.Filter(options.LoopbackAddress, netip.Addr.Is4),