Add a feature for mapping a host unix socket to a guest tcp socket

This patch adds the ability to map a host unix socket to a guest tcp socket when
using the slirp backend. This feature was added in libslirp version 4.7.0.

A new syntax for unix socket: -hostfwd=unix:hostpath-[guestaddr]:guestport

Signed-off-by: Viktor Kurilko <murlockkinght@gmail.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-ID: <20250808143904.363907-1-murlockkinght@gmail.com>

docs/system/devices/net.rst

@@ -79,7 +79,7 @@ those sockets. To allow ping for GID 100 (usually users group)::
 
 When using the built-in TFTP server, the router is also the TFTP server.
 
-When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP
+When using the ``'-netdev user,hostfwd=...'`` option, TCP, UDP or UNIX
 connections can be redirected from the host to the guest. It allows for
 example to redirect X11, telnet or SSH connections.
 

hmp-commands.hx

@@ -1357,8 +1357,8 @@ ERST
     {
         .name       = "hostfwd_add",
         .args_type  = "arg1:s,arg2:s?",
-        .params     = "[netdev_id] [tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport",
-        .help       = "redirect TCP or UDP connections from host to guest (requires -net user)",
+        .params     = "[netdev_id] [tcp|udp|unix]:[[hostaddr]:hostport|hostpath]-[guestaddr]:guestport",
+        .help       = "redirect TCP, UDP or UNIX connections from host to guest (requires -net user)",
         .cmd        = hmp_hostfwd_add,
     },
 #endif

net/slirp.c

@@ -732,6 +732,7 @@ static SlirpState *slirp_lookup(Monitor *mon, const char *id)
 
 void hmp_hostfwd_remove(Monitor *mon, const QDict *qdict)
 {
+    /* TODO: support removing unix fwd */
     struct sockaddr_in host_addr = {
         .sin_family = AF_INET,
         .sin_addr = {
@@ -800,12 +801,13 @@ void hmp_hostfwd_remove(Monitor *mon, const QDict *qdict)
 
 static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
 {
-    struct sockaddr_in host_addr = {
-        .sin_family = AF_INET,
-        .sin_addr = {
-            .s_addr = INADDR_ANY,
-        },
-    };
+    union {
+        struct sockaddr_in in;
+#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
+        struct sockaddr_un un;
+#endif
+    } host_addr = {0};
+
     struct sockaddr_in guest_addr = {
         .sin_family = AF_INET,
         .sin_addr = {
@@ -816,9 +818,13 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
     int host_port, guest_port;
     const char *p;
     char buf[256];
-    int is_udp;
+    int is_udp = 0;
+#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
+    int is_unix = 0;
+#endif
     const char *end;
     const char *fail_reason = "Unknown reason";
+    socklen_t host_addr_size;
 
     p = redir_str;
     if (!p || get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
@@ -829,30 +835,83 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
         is_udp = 0;
     } else if (!strcmp(buf, "udp")) {
         is_udp = 1;
-    } else {
+    }
+#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
+    else if (!strcmp(buf, "unix")) {
+        is_unix = 1;
+    }
+#endif
+    else {
         fail_reason = "Bad protocol name";
         goto fail_syntax;
     }
 
-    if (get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
-        fail_reason = "Missing : separator";
-        goto fail_syntax;
-    }
-    if (buf[0] != '\0' && !inet_aton(buf, &host_addr.sin_addr)) {
-        fail_reason = "Bad host address";
-        goto fail_syntax;
-    }
+#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
+    if (is_unix) {
+        if (get_str_sep(buf, sizeof(buf), &p, '-') < 0) {
+            fail_reason = "Missing - separator";
+            goto fail_syntax;
+        }
+        if (buf[0] == '\0') {
+            fail_reason = "Missing unix socket path";
+            goto fail_syntax;
+        }
+        if (buf[0] != '/') {
+            fail_reason = "unix socket path must be absolute";
+            goto fail_syntax;
+        }
 
-    if (get_str_sep(buf, sizeof(buf), &p, '-') < 0) {
-        fail_reason = "Bad host port separator";
-        goto fail_syntax;
+        size_t path_len = strlen(buf);
+        if (path_len > sizeof(host_addr.un.sun_path) - 1) {
+            fail_reason = "Unix socket path is too long";
+            goto fail_syntax;
+        }
+
+        struct stat st;
+        if (stat(buf, &st) == 0) {
+            if (!S_ISSOCK(st.st_mode)) {
+                fail_reason = "file exists and it's not unix socket";
+                goto fail_syntax;
+            }
+
+            if (unlink(buf) < 0) {
+                error_setg_errno(errp, errno, "Failed to unlink '%s'", buf);
+                goto fail_syntax;
+            }
+        }
+        host_addr.un.sun_family = AF_UNIX;
+        memcpy(host_addr.un.sun_path, buf, path_len);
+        host_addr_size = sizeof(host_addr.un);
+    } else
+#endif
+    {
+        host_addr.in.sin_family = AF_INET;
+        host_addr.in.sin_addr.s_addr = INADDR_ANY;
+
+        if (get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
+            fail_reason = "Missing : separator";
+            goto fail_syntax;
+        }
+
+        if (buf[0] != '\0' && !inet_aton(buf, &host_addr.in.sin_addr)) {
+            fail_reason = "Bad host address";
+            goto fail_syntax;
+        }
+
+        if (get_str_sep(buf, sizeof(buf), &p, '-') < 0) {
+            fail_reason = "Bad host port separator";
+            goto fail_syntax;
+        }
+
+        err = qemu_strtoi(buf, &end, 0, &host_port);
+        if (err || host_port < 0 || host_port > 65535) {
+            fail_reason = "Bad host port";
+            goto fail_syntax;
+        }
+
+        host_addr.in.sin_port = htons(host_port);
+        host_addr_size = sizeof(host_addr.in);
     }
-    err = qemu_strtoi(buf, &end, 0, &host_port);
-    if (err || host_port < 0 || host_port > 65535) {
-        fail_reason = "Bad host port";
-        goto fail_syntax;
-    }
-    host_addr.sin_port = htons(host_port);
 
     if (get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
         fail_reason = "Missing guest address";
@@ -872,12 +931,13 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
 
 #if SLIRP_CHECK_VERSION(4, 5, 0)
     err = slirp_add_hostxfwd(s->slirp,
-            (struct sockaddr *) &host_addr, sizeof(host_addr),
+            (struct sockaddr *) &host_addr, host_addr_size,
             (struct sockaddr *) &guest_addr, sizeof(guest_addr),
             is_udp ? SLIRP_HOSTFWD_UDP : 0);
 #else
+    (void) host_addr_size;
     err = slirp_add_hostfwd(s->slirp, is_udp,
-            host_addr.sin_addr, host_port,
+            host_addr.in.sin_addr, host_port,
             guest_addr.sin_addr, guest_port);
 #endif
 

qapi/net.json

@@ -281,7 +281,7 @@
 #
 # @smbserver: IP address of the built-in SMB server
 #
-# @hostfwd: redirect incoming TCP or UDP host connections to guest
+# @hostfwd: redirect incoming TCP, UDP or UNIX host connections to guest
 #     endpoints
 #
 # @guestfwd: forward guest TCP connections

qemu-options.hx

@@ -3324,8 +3324,8 @@ SRST
 
         Note that a SAMBA server must be installed on the host OS.
 
-    ``hostfwd=[tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport``
-        Redirect incoming TCP or UDP connections to the host port
+    ``hostfwd=[tcp|udp|unix]:[[hostaddr]:hostport|hostpath]-[guestaddr]:guestport``
+        Redirect incoming TCP, UDP or UNIX connections to the host port
         hostport to the guest IP address guestaddr on guest port
         guestport. If guestaddr is not specified, its value is x.x.x.15
         (default first address given by the built-in DHCP server). By
@@ -3355,6 +3355,13 @@ SRST
         Then when you use on the host ``telnet localhost 5555``, you
         connect to the guest telnet server.
 
+        To redirect host unix socket /tmp/vm to guest tcp socket 23 use
+        following:
+
+        .. parsed-literal::
+            # on the host
+            |qemu_system| -nic user,hostfwd=unix:/tmp/vm-:23
+
     ``guestfwd=[tcp]:server:port-dev``; \ ``guestfwd=[tcp]:server:port-cmd:command``
         Forward guest TCP connections to the IP address server on port
         port to the character device dev or to a program executed by