From 02a9e046fdcda632cabe9c4fc3a658f2b3447f0c Mon Sep 17 00:00:00 2001
From: Lurker00 <Lurker00@users.noreply.github.com>
Date: Tue, 10 Sep 2024 21:10:11 +0300
Subject: [PATCH] Transparent proxy mode (#114)

* Transparent proxy

* Typo errors

* long long -> intmax_t for printing time_t

---------

Co-authored-by: vel21ripn <>
Co-authored-by: Konstantin Saliy <ksaliy@s-terra.ru>
---
 extend.c |  2 +-
 main.c   | 12 ++++++++++++
 params.h |  1 +
 proxy.c  | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
 4 files changed, 67 insertions(+), 6 deletions(-)

diff --git a/extend.c b/extend.c
index ee07b2c..a9395bb 100644
--- a/extend.c
+++ b/extend.c
@@ -85,7 +85,7 @@ int mode_add_get(struct sockaddr_ina *dst, int m)
     }
     time(&t);
     if (t > val->time + params.cache_ttl) {
-        LOG(LOG_S, "time=%ld, now=%ld, ignore\n", val->time, t);
+        LOG(LOG_S, "time=%jd, now=%jd, ignore\n", (intmax_t)val->time, (intmax_t)t);
         return 0;
     }
     return val->m;
diff --git a/main.c b/main.c
index 7e95145..a299b73 100644
--- a/main.c
+++ b/main.c
@@ -61,6 +61,9 @@ struct params params = {
 const char help_text[] = {
     "    -i, --ip, <ip>            Listening IP, default 0.0.0.0\n"
     "    -p, --port <num>          Listening port, default 1080\n"
+    #ifdef __linux__
+    "    -E, --transparent         Transparent proxy mode\n"
+    #endif
     "    -c, --max-conn <count>    Connection count limit, default 512\n"
     "    -N, --no-domain           Deny domain resolving\n"
     "    -U, --no-udp              Deny UDP association\n"
@@ -116,6 +119,9 @@ const struct option options[] = {
     {"version",       0, 0, 'v'},
     {"ip",            1, 0, 'i'},
     {"port",          1, 0, 'p'},
+    #ifdef __linux__
+    {"transparent",   0, 0, 'E'},
+    #endif
     {"conn-ip",       1, 0, 'I'},
     {"buf-size",      1, 0, 'b'},
     {"max-conn",      1, 0, 'c'},
@@ -492,6 +498,11 @@ int main(int argc, char **argv)
         case 'U':
             params.udp = 0;
             break;
+        #ifdef __linux__
+        case 'E':
+            params.transparent = 1;
+            break;
+        #endif
             
         case 'h':
             printf(help_text);
@@ -868,6 +879,7 @@ int main(int argc, char **argv)
         clear_params();
         return -1;
     }
+
     int status = run((struct sockaddr_ina *)&params.laddr);
     clear_params();
     return status;
diff --git a/params.h b/params.h
index d7b03e1..13a27fc 100644
--- a/params.h
+++ b/params.h
@@ -105,6 +105,7 @@ struct params {
     size_t bfsize;
     struct sockaddr_in6 baddr;
     struct sockaddr_in6 laddr;
+    char transparent;
     struct mphdr *mempool;
     
     char *protect_path;
diff --git a/proxy.c b/proxy.c
index d01e924..42a876d 100644
--- a/proxy.c
+++ b/proxy.c
@@ -32,9 +32,13 @@
     #if defined(__linux__) && defined(__GLIBC__)
         extern int accept4(int, struct sockaddr *__restrict, socklen_t *__restrict, int);
     #endif
+    #ifdef __linux__
+        /* For SO_ORIGINAL_DST only (which is 0x50) */
+        #include "linux/netfilter_ipv4.h"
+    #endif
 #endif
 
-    
+
 int NOT_EXIT = 1;
 
 static void on_cancel(int sig) {
@@ -197,6 +201,17 @@ int resp_error(int fd, int e, int flag)
         }
         return resp_s5_error(fd, e);
     }
+    #ifdef __linux__
+    if (params.transparent &&
+            (e == ECONNREFUSED || e == ETIMEDOUT)) {
+        struct linger l = { .l_onoff = 1 };
+        if (setsockopt(fd, 
+                SOL_SOCKET, SO_LINGER, &l, sizeof(l)) < 0) {
+            uniperror("setsockopt SO_LINGER");
+            return -1;
+        }
+    }
+    #endif
     return 0;
 }
 
@@ -242,7 +257,7 @@ int s5_get_addr(char *buffer, size_t n,
         struct sockaddr_ina *addr, int type) 
 {
     if (n < S_SIZE_MIN) {
-        LOG(LOG_E, "ss: request to small\n");
+        LOG(LOG_E, "ss: request too small\n");
         return -S_ER_GEN;
     }
     struct s5_req *r = (struct s5_req *)buffer;
@@ -519,6 +534,34 @@ int udp_associate(struct poolhd *pool,
     return 0;
 }
 
+#ifdef __linux__
+static inline int transp_conn(struct poolhd *pool, struct eval *val)
+{
+    struct sockaddr_ina remote, self;
+    socklen_t rlen = sizeof(remote), slen = sizeof(self);
+    if (getsockopt(val->fd,
+            IPPROTO_IP, SO_ORIGINAL_DST, &remote, &rlen) != 0) {
+        uniperror("getsockopt SO_ORIGINAL_DST");
+        return -1;
+    }
+    if (getsockname(val->fd, &self.sa, &slen) < 0) {
+        uniperror("getsockname");
+        return -1;
+    }
+    if (self.sa.sa_family == remote.sa.sa_family && 
+            self.in.sin_port == remote.in.sin_port && 
+                addr_equ(&self, &remote)) {
+        LOG(LOG_E, "connect to self, ignore\n");
+        return -1;
+    }
+    int error = connect_hook(pool, val, &remote, EV_CONNECT);
+    if (error) {
+        uniperror("connect_hook");
+        return -1;
+    }
+    return 0;
+}
+#endif
 
 static inline int on_accept(struct poolhd *pool, struct eval *val)
 {
@@ -565,6 +608,12 @@ static inline int on_accept(struct poolhd *pool, struct eval *val)
             continue;
         }
         rval->in6 = client.in6;
+        #ifdef __linux__
+        if (params.transparent && transp_conn(pool, rval) < 0) {
+            close(c);
+            continue;
+        }
+        #endif
     }
     return 0;
 }
@@ -753,7 +802,7 @@ static inline int on_request(struct poolhd *pool, struct eval *val,
             return 0;
         }
         if (n < S_SIZE_MIN) {
-            LOG(LOG_E, "ss: request to small (%zd)\n", n);
+            LOG(LOG_E, "ss: request too small (%zd)\n", n);
             return -1;
         }
         struct s5_req *r = (struct s5_req *)buffer;
@@ -844,7 +893,7 @@ void close_conn(struct poolhd *pool, struct eval *val)
 }
 
 
-int event_loop(int srvfd) 
+int event_loop(int srvfd)
 {
     size_t bfsize = params.bfsize;
     
@@ -982,4 +1031,3 @@ int run(struct sockaddr_ina *srv)
     }
     return event_loop(fd);
 }
-