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: 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.

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

src/proxymain.c

@@ -7,6 +7,31 @@
 */
 
 #include "proxy.h"
+
+#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
+
 #ifdef __linux__
 #include <sched.h>
 #endif
@@ -84,7 +109,7 @@ 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;
@@ -687,7 +712,12 @@ int MODULEMAINFUNC (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
+	    )) {
 #ifndef STDMAIN
 		haveerror = 1;
 #endif
@@ -870,6 +900,9 @@ int MODULEMAINFUNC (int argc, char** argv){
 			return -3;
 		}
 	}
+#ifdef WITH_UN
+	unbound(&srv);
+#endif
  	if(!isudp){
 		if(srv.so._listen (srv.so.state, sock, srv.backlog?srv.backlog : 1+(srv.maxchild>>3))==-1) {
 			sprintf((char *)buf, "listen(): %s", strerror(errno));
@@ -1020,7 +1053,7 @@ int MODULEMAINFUNC (int argc, char** argv){
 					continue;
 				}
 
-				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);
 					new_sock = INVALID_SOCKET;
 					usleep(SLEEPTIME);
@@ -1320,7 +1353,7 @@ void srvfree(struct srvparam * srv){
  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

@@ -92,7 +92,6 @@ 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;
@@ -246,8 +245,7 @@ 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, NULL, 0);
-		res = param->srv->so._sendto(param->sostate, param->remsock, (char *)param->clibuf + param->clioffset, (int)MIN(inclientbuf, fromclient), 0, (struct sockaddr*)&param->sinsr, sasize);
 		if(res <= 0) {
 			TOSERVER = 0;
 			if(errno && errno != EAGAIN && errno != EINTR){
@@ -293,8 +291,7 @@ 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, NULL, 0);
-		res = param->srv->so._sendto(param->sostate, param->clisock, (char *)param->srvbuf + param->srvoffset, (int)MIN(inserverbuf,fromserver), 0, (struct sockaddr*)&param->sincr, sasize);
 		if(res <= 0) {
 			TOCLIENT = 0;
 			if(errno && errno != EAGAIN && errno != EINTR){
@@ -485,8 +482,7 @@ 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, NULL, NULL);
-			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);
 			if(res <= 0) {
 				FROMCLIENT = 0;
 				if(res == 0) {
@@ -518,8 +514,7 @@ 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, NULL, NULL);
-			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);
 			if(res <= 0) {
 				FROMSERVER = 0;
 				if(res == 0) {

src/socks.c

@@ -227,7 +227,7 @@ 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) {
@@ -246,7 +246,7 @@ fflush(stderr);
 		sin = param->sincl;
 		*SAPORT(&sin) = 0;
 		if(param->srv->so._bind(param->sostate, param->clisock,(struct sockaddr *)&sin,SASIZE(&sin))) {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

@@ -105,6 +105,7 @@ int
 
 #ifdef WITH_UN
 #include <sys/un.h>
+#include <stddef.h>
 #endif
 
 #define ALLOW		0
@@ -152,7 +153,9 @@ 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)
@@ -527,6 +530,8 @@ 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

@@ -136,7 +136,7 @@ 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;