Unix sockets: no addresses on streams, abstract names, tcppm port 0

On Linux a proxy listening on a Unix socket relayed only the first
bytes of an answer (result 95): sockmap() read with recvfrom() into the
client's address, which for a Unix stream socket Linux fills with an
empty AF_UNIX one, and then sent with sendto() to that address, which a
connected Unix stream socket refuses. A TCP connection has no use for
addresses: sockmap() now sends and receives with NULL ones, and
connect-back sends its command with socksend() and reads the answer
with sockrecvfrom() without an address, which a NULL sin now allows.

An abstract socket name (-iunix:@NAME) was bound with the whole size of
struct sockaddr_un, padded with zeros, so a client naming it by its
bytes, as most do, reached another name. SASIZE() now gives an abstract
address its exact size; getsockname() calls that took SASIZE() of the
old contents as the buffer size take the buffer's size instead.

tcppm refused port 0 for a unix: target, though the manual gives
"tcppm 8080 unix:/var/run/app.sock 0" as the example: the port of a
Unix socket target is ignored, so 0 is allowed.

On a reload the new service bound the path anew and the old one,
closing after it, removed the file, the new service's by then, leaving
nothing to connect to. A service now notes the file it bound (device
and inode) and removes the path on closing only if it is still that
file.

A test case covers a proxy on a Unix socket and on an abstract one on
Linux, tcppm to a Unix socket, a parent reached through one, and a
listening Unix socket across reloads: its file kept and the proxy
answering, and the file removed once no service listens on it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/proxymain.c

@@ -84,7 +84,7 @@ void * threadfunc (void *p) {
 			continue;
 		}
 #endif
-		if(socksendto(param, param->remsock, (struct sockaddr*)&param->sinsr, (unsigned char *)"C", 1, CONNBACK_TO*1000) != 1){
+		if(socksend(param, param->remsock, (unsigned char *)"C", 1, CONNBACK_TO) != 1){
 			dolog(param, (unsigned char *)"Connect back sending command failed");
 			param->srv->so._closesocket(param->sostate, param->remsock);
 			param->remsock = INVALID_SOCKET;
@@ -705,7 +705,12 @@ static int srvprepare(struct srvstart *s, int argc, char **argv){
  else {
 #endif
 #ifndef NOPORTMAP
-	if (error || argc != i+3 || *argv[i]=='-'|| (*SAPORT(&srv->intsa) = htons((uint16_t)atoi(argv[i])))==0 || (srv->targetport = htons((uint16_t)atoi(argv[i+2])))==0) {
+	/* the port of a Unix socket target is ignored, 0 as the manual has it */
+	if (error || argc != i+3 || *argv[i]=='-'|| (*SAPORT(&srv->intsa) = htons((uint16_t)atoi(argv[i])))==0 || ((srv->targetport = htons((uint16_t)atoi(argv[i+2])))==0
+#ifdef WITH_UN
+	    && strncmp(argv[i+1], "unix:", 5)
+#endif
+	    )) {
 		fprintf(stderr, "%s of %s\n"
 			"Usage: %s options"
 			" [-e<external_ip>] <port_to_bind>"
@@ -761,6 +766,11 @@ static int srvprepare(struct srvstart *s, int argc, char **argv){
 
 /* The listening socket. A UDP one also receives the datagrams of new
    clients, so it is their client socket too. 0, or the code to exit with. */
+#ifdef WITH_UN
+static void unbound(struct srvparam *srv);
+static void ununlink(struct srvparam *srv);
+#endif
+
 static int srvlisten(struct srvstart *s){
  struct srvparam *srv = &s->srv;
  struct clientparam *defparam = &s->defparam;
@@ -815,6 +825,9 @@ static int srvlisten(struct srvstart *s){
 	sleeptime = (sleeptime<<1);
 	if(!sleeptime) return -3;
  }
+#ifdef WITH_UN
+ unbound(srv);
+#endif
 #ifndef NOTCPMAIN
  if(!s->isudp){
 	if(srv->so._listen (srv->so.state, sock, srv->backlog?srv->backlog : 1+(srv->maxchild>>3))==-1) {
@@ -909,7 +922,7 @@ static int tcpnext(struct srvstart *s, SOCKET *client, int *nlog){
 		return NEXT_RETRY;
 	}
 
-	if(sockrecvfrom(NULL, new_sock,(struct sockaddr*)&defparam->sincr,buf,1,60*1000) != 1 || *buf!='C') {
+	if(sockrecvfrom(NULL, new_sock, NULL, buf, 1, 60*1000) != 1 || *buf!='C') {
 		so._closesocket(so.state, new_sock);
 		usleep(SLEEPTIME);
 		return NEXT_RETRY;
@@ -1478,13 +1491,37 @@ void srvinit2(struct srvparam * srv, struct clientparam *param){
 	param->sinsr = srv->extsa;
 }
 
+#ifdef WITH_UN
+/* A service bound to a Unix socket path notes its file, as a service of a
+   newer configuration may bind the same path before this one closes: the
+   file is then the other's, which closing must not remove. */
+static void unbound(struct srvparam *srv){
+ struct stat st;
+
+ if(*SAFAMILY(&srv->intsa) == AF_UNIX && *SAADDR(&srv->intsa) &&
+    !stat((char *)SAADDR(&srv->intsa), &st)){
+	srv->undev = (uint64_t)st.st_dev;
+	srv->unino = (uint64_t)st.st_ino;
+ }
+}
+
+static void ununlink(struct srvparam *srv){
+ struct stat st;
+
+ if(*SAFAMILY(&srv->intsa) == AF_UNIX && *SAADDR(&srv->intsa) &&
+    !stat((char *)SAADDR(&srv->intsa), &st) &&
+    (uint64_t)st.st_dev == srv->undev && (uint64_t)st.st_ino == srv->unino)
+	unlink((char *)SAADDR(&srv->intsa));
+}
+#endif
+
 void srvfree(struct srvparam * srv){
  int i;
 
  if(srv->srvsock != INVALID_SOCKET) {
     so._closesocket(srv->so.state, srv->srvsock);
 #ifdef WITH_UN
-    if(*SAFAMILY(&srv->intsa) == AF_UNIX && *SAADDR(&srv->intsa))unlink((char *)SAADDR(&srv->intsa));
+    ununlink(srv);
 #endif
  }
  srv->srvsock = INVALID_SOCKET;

src/sockgetchar.c

@@ -64,8 +64,9 @@ int sockrecvfrom(struct clientparam *param, SOCKET sock, struct sockaddr * sin,
 	res = param?param->srv->so._poll(param->sostate, &fds, 1, to):so._poll(so.state, &fds, 1, to);
 	if (res<1) return 0;
 	sasize = sizeof(PROXYSOCKADDRTYPE);
+	/* sin NULL for a stream socket: nothing to learn the address into */
 	do {
-		res = param?param->srv->so._recvfrom(param->sostate, sock, (char *)buf, bufsize, 0, (struct sockaddr *)sin, &sasize):so._recvfrom(so.state, sock, (char *)buf, bufsize, 0, (struct sockaddr *)sin, &sasize);
+		res = param?param->srv->so._recvfrom(param->sostate, sock, (char *)buf, bufsize, 0, (struct sockaddr *)sin, sin? &sasize : NULL):so._recvfrom(so.state, sock, (char *)buf, bufsize, 0, (struct sockaddr *)sin, sin? &sasize : NULL);
 	} while (res < 0 && (errno == EAGAIN || errno == EINTR));
 	return res;
 }

src/sockmap.c

@@ -107,7 +107,6 @@ int sockmap(struct clientparam * param, int timeo, int usesplice){
  int sleeptime = 0;
  FILTER_ACTION action;
  int res = 0;
- SASIZETYPE sasize;
  int needaction = 0;
  int graceclinum=0, gracesrvnum=0, graceclitraf=0, gracesrvtraf=0;
  time_t gracetime = 0;
@@ -275,8 +274,9 @@ log("send to server from buf");
 			param->clioffset = param->cliinbuf = 0;
 			if(fromclient) TOCLIENTBUF = 1;
 		}
-		sasize = SASIZE(&param->sinsr);
-		res = param->srv->so._sendto(param->sostate, param->remsock, (char *)param->clibuf + param->clioffset, (int)MIN(inclientbuf, fromclient), 0, (struct sockaddr*)&param->sinsr, sasize);
+		/* a connected stream: no address, which a Unix socket on Linux
+		   would refuse */
+		res = param->srv->so._sendto(param->sostate, param->remsock, (char *)param->clibuf + param->clioffset, (int)MIN(inclientbuf, fromclient), 0, NULL, 0);
 		if(res <= 0) {
 			TOSERVER = 0;
 			if(errno && errno != EAGAIN && errno != EINTR){
@@ -322,8 +322,7 @@ log("send to client from buf");
 			if(fromserver) TOSERVERBUF = 1;
 			continue;
 		}
-		sasize = SASIZE(&param->sincr);
-		res = param->srv->so._sendto(param->sostate, param->clisock, (char *)param->srvbuf + param->srvoffset, (int)MIN(inserverbuf,fromserver), 0, (struct sockaddr*)&param->sincr, sasize);
+		res = param->srv->so._sendto(param->sostate, param->clisock, (char *)param->srvbuf + param->srvoffset, (int)MIN(inserverbuf,fromserver), 0, NULL, 0);
 		if(res <= 0) {
 			TOCLIENT = 0;
 			if(errno && errno != EAGAIN && errno != EINTR){
@@ -543,8 +542,9 @@ log("done read from server to pipe\n");
 #ifdef WITHLOG
 log("read from client to buf");
 #endif
-			sasize = sizeof(param->sincr);
-			res = param->srv->so._recvfrom(param->sostate, param->clisock, (char *)param->clibuf + param->cliinbuf, (int)MIN((uint64_t)param->clibufsize - param->cliinbuf, fromclient-inclientbuf), 0, (struct sockaddr *)&param->sincr, &sasize);
+			/* no address: it would overwrite the client's with what a
+			   stream socket gives, an empty one for a Unix socket */
+			res = param->srv->so._recvfrom(param->sostate, param->clisock, (char *)param->clibuf + param->cliinbuf, (int)MIN((uint64_t)param->clibufsize - param->cliinbuf, fromclient-inclientbuf), 0, NULL, NULL);
 			if(res <= 0) {
 				FROMCLIENT = 0;
 				if(res == 0) {
@@ -587,8 +587,7 @@ log("done read from client to buf");
 #ifdef WITHLOG
 log("read from server to buf");
 #endif
-			sasize = sizeof(param->sinsr);
-			res = param->srv->so._recvfrom(param->sostate, param->remsock, (char *)param->srvbuf + param->srvinbuf, (int)MIN((uint64_t)param->srvbufsize - param->srvinbuf, fromserver-inserverbuf), 0, (struct sockaddr *)&param->sinsr, &sasize);
+			res = param->srv->so._recvfrom(param->sostate, param->remsock, (char *)param->srvbuf + param->srvinbuf, (int)MIN((uint64_t)param->srvbufsize - param->srvinbuf, fromserver-inserverbuf), 0, NULL, NULL);
 			if(res <= 0) {
 				FROMSERVER = 0;
 				if(res == 0) {

src/socks.c

@@ -230,7 +230,7 @@ fprintf(stderr, "%hu bound to communicate with server\n", *SAPORT(&param->sinsl)
 fflush(stderr);
 #endif
 	}
-	sasize = SASIZE(&param->sinsl);
+	sasize = sizeof(param->sinsl);
 	param->srv->so._getsockname(param->sostate, param->remsock, (struct sockaddr *)&param->sinsl,  &sasize);
  }
  if(command == 3) {
@@ -250,7 +250,7 @@ fflush(stderr);
 		*SAPORT(&sin) = 0;
 		/* the port the client is told to send its datagrams to */
 		if(bindwithrange(param, param->clisock, &sin, param->intport)) {RETURN (12);}
-		sasize = SASIZE(&sin);
+		sasize = sizeof(sin);
 		param->srv->so._getsockname(param->sostate, param->clisock, (struct sockaddr *)&sin, &sasize);
 #if SOCKSTRACE > 0
 fprintf(stderr, "%hu binded to communicate with client\n",

src/structures.h

@@ -113,6 +113,7 @@ int
 
 #ifdef WITH_UN
 #include <sys/un.h>
+#include <stddef.h>
 #endif
 
 #define ALLOW		0
@@ -160,7 +161,9 @@ int
 #define	UN_SAADDR(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? (unsigned char *)((struct sockaddr_un *)sa)->sun_path :
 #define	UN_SAADDRLEN(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? (int)sizeof(((struct sockaddr_un *)sa)->sun_path) :
 #define	UN_SASOCK(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? PF_UNIX :
-#define	UN_SASIZE(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? sizeof(struct sockaddr_un) :
+/* an abstract name (Linux) is its bytes after the leading 0, no more:
+   padded with zeros it would be another name */
+#define	UN_SASIZE(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? (((struct sockaddr_un *)sa)->sun_path[0] || !((struct sockaddr_un *)sa)->sun_path[1]? sizeof(struct sockaddr_un) : offsetof(struct sockaddr_un, sun_path) + 1 + strlen(((struct sockaddr_un *)sa)->sun_path + 1)) :
 #define	UN_SAISNULL(sa) (((struct sockaddr_un *)sa)->sun_family == AF_UNIX)? (((struct sockaddr_un *)sa)->sun_path[0] == 0 && ((struct sockaddr_un *)sa)->sun_path[1] == 0) :
 #else
 #define UN_SAPORT(sa)
@@ -608,6 +611,8 @@ struct srvparam {
 	AUTHFUNC authfunc;
 	PROXYFUNC pf;
 	SOCKET srvsock, cbsock;
+	/* the file of a Unix socket bound to a path, to remove only it */
+	uint64_t undev, unino;
 	int childcount;
 	int maxchild;
 	int backlog;

src/udpsockmap.c

@@ -140,7 +140,7 @@ int udpbind(struct clientparam *param)
 			return 12;
 		}
 	}
-	sasize = SASIZE(&param->sinsl);
+	sasize = sizeof(param->sinsl);
 	param->srv->so._getsockname(param->sostate, param->remsock,
 			(struct sockaddr *)&param->sinsl, &sasize);
 	return 0;

tests/cases/unixsock.py

@@ -0,0 +1,139 @@
+"""Unix domain sockets: a service listening on one (-iunix:PATH, and on
+Linux an abstract -iunix:@NAME), tcppm forwarding to one (DSTADDR
+unix:PATH), a parent reached through one (parent ... unix:PATH), and a
+listening one across reloads: each reload's service binding it anew, its
+file kept while a service listens on it and removed once none does."""
+
+import os
+import socket
+import sys
+import time
+
+
+def unix_get(path, url, timeout=10):
+    """A GET for url sent to the proxy at the Unix socket path (a leading @
+    for an abstract one): (status, body length), or (None, error)."""
+    s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    s.settimeout(timeout)
+    try:
+        s.connect("\0" + path[1:] if path.startswith("@") else path)
+        s.sendall(f"GET {url} HTTP/1.0\r\nHost: unix\r\n\r\n".encode())
+        got = b""
+        while True:
+            b = s.recv(65536)
+            if not b:
+                break
+            got += b
+    except OSError as e:
+        return None, str(e)
+    finally:
+        s.close()
+    head, _, body = got.partition(b"\r\n\r\n")
+    try:
+        return int(head.split()[1]), len(body)
+    except (IndexError, ValueError):
+        return None, head[:80]
+
+
+def run(t):
+    if not hasattr(socket, "AF_UNIX") or sys.platform.startswith("win"):
+        t.skip("Unix domain sockets (not on this platform)")
+        return
+
+    origin = t.free_port()
+    mapped = t.free_port()
+    chained = t.free_port()
+    adm = t.free_port()
+    path = os.path.join(t.tmpdir, "px.sock")
+    abstract = f"@3proxy-test-{os.getpid()}" if sys.platform.startswith("linux") else None
+    url = f"http://127.0.0.1:{origin}/data?size=1000"
+
+    def config(unix=True):
+        services = f"""
+            flush
+            auth iponly
+            allow *
+            proxy -iunix:{path}
+        """ if unix else ""
+        if unix and abstract:
+            services += f"""
+            proxy -iunix:{abstract}
+        """
+        if unix:
+            services += f"""
+            flush
+            auth iponly
+            allow *
+            tcppm {mapped} unix:{path} 0
+
+            flush
+            auth iponly
+            allow *
+            parent 1000 http unix:{path} 0
+            proxy -p{chained}
+        """
+        return f"""
+            log
+            auth iponly
+            allow *
+            http data * /data
+            httpsrv -p{origin}
+            {services}
+            flush
+            auth iponly
+            allow *
+            admin -p{adm}
+        """
+
+    server = t.start("unixsock", config(), ports=[origin, mapped, chained, adm])
+    # a build without Unix sockets (NO_UN) never makes the file
+    deadline = time.time() + 5
+    while time.time() < deadline and not os.path.exists(path):
+        time.sleep(0.05)
+    if not os.path.exists(path):
+        t.skip("Unix domain sockets (not supported by this build)")
+        return
+
+    # --- a proxy listening on a Unix socket ---------------------------------
+    t.eq((200, 1000), unix_get(path, url), "a proxy listening on a Unix socket answers")
+    if abstract:
+        t.eq((200, 1000), unix_get(abstract, url),
+             "a proxy listening on an abstract Unix socket answers")
+
+    # --- tcppm forwarding to a Unix socket: the proxy behind it answers -----
+    r = t.http(url, proxy=f"127.0.0.1:{mapped}")
+    t.eq(200, r.status, "tcppm forwards a TCP port to a Unix socket")
+    t.eq(1000, r.length, "and the whole answer comes back through it")
+
+    # --- a parent reached through a Unix socket ------------------------------
+    r = t.http(url, proxy=f"127.0.0.1:{chained}")
+    t.eq(200, r.status, "a proxy chains to a parent on a Unix socket")
+    t.eq(1000, r.length, "and the whole answer comes back through the chain")
+
+    # --- reloads: each new service binds the path anew; the old one, closing
+    # after, must not remove the new one's file ----------------------------
+    for i in range(3):
+        before = server.output().count("Accepting connections")
+        t.write_config("unixsock", config())
+        t.http(f"http://127.0.0.1:{adm}/R")
+        deadline = time.time() + 10
+        while time.time() < deadline and server.output().count("Accepting connections") < before + 5:
+            time.sleep(0.05)
+    # the old services stop within a second of each reload
+    time.sleep(1.5)
+    t.ok("after three reloads the socket file is still there") if os.path.exists(path) else \
+        t.fail("after three reloads the socket file is still there", path, "missing")
+    t.eq((200, 1000), unix_get(path, url), "and the proxy answers on it")
+
+    # --- no service listens there any more: the file goes -------------------
+    t.write_config("unixsock", config(unix=False))
+    t.http(f"http://127.0.0.1:{adm}/R")
+    deadline = time.time() + 5
+    while time.time() < deadline and os.path.exists(path):
+        time.sleep(0.1)
+    t.ok("once no service listens on it the socket file is removed") \
+        if not os.path.exists(path) else \
+        t.fail("once no service listens on it the socket file is removed", "no file", path)
+    got = unix_get(path, url, timeout=2)
+    t.ok("and nothing answers there") if got[0] is None else \
+        t.fail("and nothing answers there", "no connection", got)