[PATCH v2] Add a feature for mapping a host unix socket to a guest tcp socket

[PATCH v2] Add a feature for mapping a host unix socket to a guest tcp socket

[Viktor Kurilko]

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.

Signed-off-by: Viktor Kurilko <murlockkinght@gmail.com>
---
Fixed checking the path length.
Fixed copying the path.
Unnecessary access has been deleted.
Unlink is needed to delete the socket remaining from the previous vm.

 net/slirp.c | 61 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 13 deletions(-)

diff --git a/net/slirp.c b/net/slirp.c
index 9657e86a84..d096ee7ce6 100644
--- a/net/slirp.c
+++ b/net/slirp.c
@@ -795,12 +795,16 @@ 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};
+    host_addr.in.sin_family = AF_INET;
+    host_addr.in.sin_addr.s_addr = INADDR_ANY;
+    socklen_t host_addr_size = sizeof(host_addr.in);
+
     struct sockaddr_in guest_addr = {
         .sin_family = AF_INET,
         .sin_addr = {
@@ -833,7 +837,7 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
         fail_reason = "Missing : separator";
         goto fail_syntax;
     }
-    if (buf[0] != '\0' && !inet_aton(buf, &host_addr.sin_addr)) {
+    if (buf[0] != '\0' && !inet_aton(buf, &host_addr.in.sin_addr)) {
         fail_reason = "Bad host address";
         goto fail_syntax;
     }
@@ -842,12 +846,43 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
         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;
+#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
+    if (buf[0] == '/') {
+        if (is_udp) {
+            fail_reason = "Mapping unix to udp is not supported";
+            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
+    {
+        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.sin_port = htons(host_port);
 
     if (get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
         fail_reason = "Missing guest address";
@@ -867,7 +902,7 @@ 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
-- 
2.50.1

Re: [PATCH v2] Add a feature for mapping a host unix socket to a guest tcp socket

[Samuel Thibault]

Hello,

Thanks for working on this!

Viktor Kurilko, le dim. 03 août 2025 12:01:04 +0700, a ecrit:
> diff --git a/net/slirp.c b/net/slirp.c
> index 9657e86a84..d096ee7ce6 100644
> --- a/net/slirp.c
> +++ b/net/slirp.c
> @@ -795,12 +795,16 @@ 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};
> +    host_addr.in.sin_family = AF_INET;
> +    host_addr.in.sin_addr.s_addr = INADDR_ANY;
> +    socklen_t host_addr_size = sizeof(host_addr.in);
> +
>      struct sockaddr_in guest_addr = {
>          .sin_family = AF_INET,
>          .sin_addr = {
> @@ -833,7 +837,7 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
>          fail_reason = "Missing : separator";
>          goto fail_syntax;
>      }
> -    if (buf[0] != '\0' && !inet_aton(buf, &host_addr.sin_addr)) {
> +    if (buf[0] != '\0' && !inet_aton(buf, &host_addr.in.sin_addr)) {

Does that not behave oddly when given a path?

Also, it's a bit odd to set host_addr for AF_INET and overwrite for the
UNIX case. Perhaps better use:

#if ..
  if (buf[0] == '/') {
    ...
    handle UNIX case
    ...
    host_addr.in.sin_family = AF_UNIX;
    host_addr_size = sizeof(host_addr.un);
  } else
#endif
  {
    ...
    handle INET case
    ...
    host_addr.in.sin_family = AF_INET;
    host_addr_size = sizeof(host_addr.in);
  }

>          fail_reason = "Bad host address";
>          goto fail_syntax;
>      }
> @@ -842,12 +846,43 @@ static int slirp_hostfwd(SlirpState *s, const char *redir_str, Error **errp)
>          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;
> +#if !defined(WIN32) && SLIRP_CHECK_VERSION(4, 7, 0)
> +    if (buf[0] == '/') {
> +        if (is_udp) {
> +            fail_reason = "Mapping unix to udp is not supported";
> +            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
> +    {
> +        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.sin_port = htons(host_port);
>  
>      if (get_str_sep(buf, sizeof(buf), &p, ':') < 0) {
>          fail_reason = "Missing guest address";
> @@ -867,7 +902,7 @@ 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
> -- 
> 2.50.1