Support Unix sockets in hostfwd

QEMU has an issue open
(https://gitlab.com/qemu-project/qemu/-/issues/347) to forward a Unix
domain socket to guest TCP port. Both of these protocols support stream
modes of operation (and user-mode networking can only access the stream
anyway), so this patch enables Unix-to-TCP hostfwds.

Like with localhost hostfwds, the sotranslate_accept function will
translate a Unix domain socket connection to a TCP connection
originating from vhost_addr and a randomized ephemeral port.

Signed-off-by: Nicholas Ngai <nicholas@ngai.me>

4 files changed, 34 insertions, 14 deletions

diff --git a/src/libslirp.h b/src/libslirp.h
index 5760d53..afb6663 100644
--- a/src/libslirp.h
+++ b/src/libslirp.h
@@ -13,6 +13,7 @@
 #else
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <sys/un.h>
 #endif
 
 #include "libslirp-version.h"
diff --git a/src/socket.c b/src/socket.c
index 2c1b789..09ce6bf 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -769,18 +769,6 @@ struct socket *tcpx_listen(Slirp *slirp,
     socklen_t addrlen;
 
     DEBUG_CALL("tcpx_listen");
-    /* AF_INET6 addresses are bigger than AF_INET, so this is big enough. */
-    char addrstr[INET6_ADDRSTRLEN];
-    char portstr[6];
-    int ret;
-    ret = getnameinfo(haddr, haddrlen, addrstr, sizeof(addrstr), portstr, sizeof(portstr), NI_NUMERICHOST|NI_NUMERICSERV);
-    g_assert(ret == 0);
-    DEBUG_ARG("haddr = %s", addrstr);
-    DEBUG_ARG("hport = %s", portstr);
-    ret = getnameinfo(laddr, laddrlen, addrstr, sizeof(addrstr), portstr, sizeof(portstr), NI_NUMERICHOST|NI_NUMERICSERV);
-    g_assert(ret == 0);
-    DEBUG_ARG("laddr = %s", addrstr);
-    DEBUG_ARG("lport = %s", portstr);
     DEBUG_ARG("flags = %x", flags);
 
     /*
@@ -1041,6 +1029,13 @@ void sotranslate_accept(struct socket *so)
         }
         break;
 
+    case AF_UNIX:
+        /* Translate Unix socket to random ephemeral source port. */
+        so->so_ffamily = AF_INET;
+        so->so_faddr = slirp->vhost_addr;
+        so->so_fport = g_rand_int_range(slirp->grand, 49152, 65536);
+        break;
+
     default:
         break;
     }
diff --git a/src/socket.h b/src/socket.h
index a73175d..5f6242e 100644
--- a/src/socket.h
+++ b/src/socket.h
@@ -6,6 +6,8 @@
 #ifndef SLIRP_SOCKET_H
 #define SLIRP_SOCKET_H
 
+#include <string.h>
+
 #include "misc.h"
 #include "sbuf.h"
 
@@ -23,6 +25,16 @@ typedef union in4or6_addr in4or6_addr;
  * Our socket structure
  */
 
+union slirp_sockaddr_host {
+    struct sockaddr sa;
+    struct sockaddr_storage ss;
+    struct sockaddr_in sin;
+    struct sockaddr_in6 sin6;
+#ifndef _WIN32
+    struct sockaddr_un sun;
+#endif
+};
+
 union slirp_sockaddr {
     struct sockaddr sa;
     struct sockaddr_storage ss;
@@ -47,11 +59,12 @@ struct socket {
     struct tcpiphdr *so_ti; /* Pointer to the original ti within
                              * so_mconn, for non-blocking connections */
     uint32_t so_urgc;
-    union slirp_sockaddr fhost; /* Foreign host */
+    union slirp_sockaddr_host fhost; /* Foreign host */
 #define so_faddr fhost.sin.sin_addr
 #define so_fport fhost.sin.sin_port
 #define so_faddr6 fhost.sin6.sin6_addr
 #define so_fport6 fhost.sin6.sin6_port
+#define so_fpath fhost.sun.sun_path
 #define so_ffamily fhost.ss.ss_family
 
     union slirp_sockaddr lhost; /* Local host */
@@ -128,6 +141,13 @@ static inline int sockaddr_equal(const struct sockaddr_storage *a,
         return (in6_equal(&a6->sin6_addr, &b6->sin6_addr) &&
                 a6->sin6_port == b6->sin6_port);
     }
+#ifndef _WIN32
+    case AF_UNIX: {
+        const struct sockaddr_un *aun = (const struct sockaddr_un *)a;
+        const struct sockaddr_un *bun = (const struct sockaddr_un *)b;
+        return strncmp(aun->sun_path, bun->sun_path, sizeof(aun->sun_path)) == 0;
+    }
+#endif
     default:
         g_assert_not_reached();
     }
@@ -142,6 +162,10 @@ static inline socklen_t sockaddr_size(const struct sockaddr_storage *a)
         return sizeof(struct sockaddr_in);
     case AF_INET6:
         return sizeof(struct sockaddr_in6);
+#ifndef _WIN32
+    case AF_UNIX:
+        return sizeof(struct sockaddr_un);
+#endif
     default:
         g_assert_not_reached();
     }
diff --git a/src/state.c b/src/state.c
index 22af77b..181d338 100644
--- a/src/state.c
+++ b/src/state.c
@@ -273,7 +273,7 @@ static const VMStateDescription vmstate_slirp_socket = {
             VMSTATE_UINT16_TEST(so_lport, struct socket, slirp_older_than_v4),
             /* v4 and newer */
             VMSTATE_STRUCT(fhost, struct socket, 4, vmstate_slirp_socket_addr,
-                           union slirp_sockaddr),
+                           union slirp_sockaddr_host),
             VMSTATE_STRUCT(lhost, struct socket, 4, vmstate_slirp_socket_addr,
                            union slirp_sockaddr),