Added option res-nsaddr

CHANGES

@@ -140,6 +140,9 @@ Features:
 	number of times to retransmit.
 	Disable them and the old res-* opts with: ./configure --disable-resolve
 
+	Added option res-nsaddr that overrides /etc/resolv.conf nameserver
+	address based on an undocumented resolver feature.
+
 Corrections:
 	When a sub process (EXEC, SYSTEM) terminated with exit code other than
 	0, its last sent data might have been lost depending on timing of read/

VERSION

@@ -1 +1 @@
-"1.7.4.5+"
+"1.7.4.5+20230721"

config.h.in

@@ -680,6 +680,7 @@
 
 #undef HAVE_RES_RETRANS
 #undef HAVE_RES_RETRY
+#undef HAVE_RES_NSADDR_LIST
 
 #undef HAVE_SETGRENT
 #undef HAVE_GETGRENT

configure.ac

@@ -2156,6 +2156,12 @@ AC_TRY_COMPILE([#include <resolv.h>],
 [AC_MSG_RESULT(yes);
  AC_DEFINE(HAVE_RES_RETRY, 1)],
  [AC_MSG_RESULT(no)])
+AC_MSG_CHECKING(for _res.nsaddr_list)
+AC_TRY_COMPILE([#include <resolv.h>],
+[_res.nsaddr_list[0].sin_family == 0],
+[AC_MSG_RESULT(yes);
+ AC_DEFINE(HAVE_RES_NSADDR_LIST, 1)],
+ [AC_MSG_RESULT(no)])
 
 
 dnl "tcpd" "tcpwrappers"

doc/socat.yo

@@ -2397,23 +2397,39 @@ label(OPTOIN_IP_TRANSPARENT)
 dit(bf(tt(ip-transparent)))
    Sets the IP_TRANSPARENT socket option.
    This option might require root privilege.
+enddit()
+
+startdit()enddit()nl()
+
+label(OPTIONS_RESOLVER)em(bf(Resolver options))
+
+These options temporarily change the behaviour of hostname resolution. The
+options of form code(ai-*) affect behaviour of the code(getaddrinfo()) function that
+includes code(/etc/hosts) and NIS based lookups.
+
+The addresses of form code(res-*) only affect DNS lookups, and only when the
+result is not cached in code(nscd). These options might not work on all
+operating systems or libc implementations.
+
+startdit()
 label(OPTION_AI_ADDRCONFIG)
-dit(bf(tt(ai-addrconfig[=0|1]))), dit(bf(tt(addrconfig[=0|1])))
+dit(bf(tt(ai-addrconfig[=0|1]))) dit(bf(tt(addrconfig[=0|1])))
    Sets or unsets the AI_ADDRCONFIG flag to prevent name resolution to address
    families that are not available on the computer (e.g. IPv6). Default value
    is 1 in case the resolver does not get an address family hint from Socat
    address or defaults.
 label(OPTION_AI_PASSIVE)
-dit(bf(tt(ai-passive[=0|1]))), dit(bf(tt(passive[=0|1])))
+dit(bf(tt(ai-passive[=0|1]))) dit(bf(tt(passive[=0|1])))
-   Sets of unsets the AI_ADDRCONFIG flag for code(getaddrinfo()) calls.
+   Sets of unsets the AI_PASSIVE flag for code(getaddrinfo()) calls.
    Default is 1 for LISTEN, RECV, and RECVFROM type addresses, and with
    link(bind)(OPTION_BIND) option. 
 label(OPTION_AI_V4MAPPED)
-dit(bf(tt(ai-v4mapped[=0|1]))), dit(bf(tt(v4mapped[=0|1])))
+dit(bf(tt(ai-v4mapped[=0|1]))) dit(bf(tt(v4mapped[=0|1])))
    Sets or unsets the AI_V4MAPPED flag for code(getaddrinfo()). With socat()
    addresses requiring IPv6 addresses, this resolves IPv4 addresses to the
    approriate IPv6 address [::ffff:*:*]. For IPv6 Socat addresses, the default
    is 1.
+
 label(OPTION_RES_DEBUG)dit(bf(tt(res-debug)))
 label(OPTION_RES_AAONLY)dit(bf(tt(res-aaonly)))
 label(OPTION_RES_USEVC)dit(bf(tt(res-usevc)))
@@ -2437,6 +2453,12 @@ label(OPTION_RES_RETRANS)dit(bf(tt(res-retrans=<int>)))
 label(OPTION_RES_RETRY)dit(bf(tt(res-retry=<int>)))
    Sets the number of retransmits of the DNS resolver (based on an undocumented
    feature).
+label(OPTION_RES_NSADDR)dit(bf(tt(res-nsaddr=<ipaddr>[:<port>])))
+   Tries to overwrite nameserver settings loaded from /etc/resolv.conf by
+   writing the given IPv4 address into the undocumented
+   code(_res:nsaddr_list[0]) field.
+   code(/etc/hosts) is still checked by resolver. Please note that glibc's
+   code(nscd) is always queried first when it is running!
 enddit()
 
 startdit()enddit()nl()
@@ -2707,6 +2729,7 @@ label(OPTION_ACCEPT_TIMEOUT)dit(bf(tt(accept-timeout=<seconds>)))
    End waiting for a connection after <seconds> [link(timeval)(TYPE_TIMEVAL)]
    with error status.
 enddit()
+
 startdit()enddit()nl()
 
 
@@ -2826,6 +2849,7 @@ label(GROUP_SHELL)
 
 Options for link(address SHELL)(ADDRESS_SHELL)
 
+startdit()
 label(OPTION_SHELL)dit(bf(tt(shell=<filename>)))
    Overwrites use the default shell with the named executable, e.g.
    tt(/bin/dash). Also sets the tt(SHELL) environment variable.
@@ -3217,6 +3241,7 @@ measures are required to get the VLAN information, see NOEXPAND(packet(7)) PACKE
 and to optionally insert the tag into the packet again, use option
 link(retrieve-vlan)(OPTION_RETRIEVE_VLAN) when you need this.
 
+startdit()
 label(OPTION_RETRIEVE_VLAN)dit(bf(tt(retrieve-vlan)))
    On packets incoming on raw sockets, retrieve the VLAN information and insert
    it into the packets for further processing (Linux)

test.sh

@@ -17287,6 +17287,80 @@ esac
 N=$((N+1))
 
 
+# Test the res-nsaddr (resolver, dns) option
+NAME=RES_NSADDR
+case "$TESTS" in
+*%$N%*|*%functions%*|*%resolv%*|*%ip4%*|*%tcp4%*|*%socket%*|*%$NAME%*)
+TEST="$NAME: test the res-nsaddr option"
+# Start a supplementary Socat instance that will receive the DNS query.
+# Run main Socat process, opening an IPv4 socket with option res-nsaddr
+# directed to the aux process.
+# When the supplementary Socat instance received the query the test succeeded.
+if ! eval $NUMCOND; then :;
+elif ! F=$(testfeats STDIO IP4 UDP TCP); then
+    $PRINTF "test $F_n $TEST... ${YELLOW}Feature $F not configured in $SOCAT${NORMAL}\n" $N
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+elif ! A=$(testaddrs STDIO TCP4 UDP-RECVFROM); then
+    $PRINTF "test $F_n $TEST... ${YELLOW}Address $A not available in $SOCAT${NORMAL}\n" $N
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+elif ! o=$(testoptions res-nsaddr) >/dev/null; then
+    $PRINTF "test $F_n $TEST... ${YELLOW}Option $o not available in $SOCAT${NORMAL}\n" $N
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+elif ! runsip4 >/dev/null; then
+    $PRINTF "test $F_n $TEST... ${YELLOW}IPv4 not available on host${NORMAL}\n" $N
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+else
+tf="$td/test$N.stdout"
+te="$td/test$N.stderr"
+tdiff="$td/test$N.diff"
+da="$(echo test$N $(date) $RANDOM |tr ' :' '-')"
+echo "$da" >"$td/test$N.da"
+newport udp4 	# or whatever proto, or drop this line
+CMD0="$TRACE $SOCAT $opts -u UDP-RECVFROM:$PORT -"
+CMD1="$TRACE $SOCAT $opts - TCP4:$da:0,res-nsaddr=$LOCALHOST:$PORT"
+printf "test $F_n $TEST... " $N
+$CMD0 >/dev/null 2>"${te}0" >"${tf}0" &
+pid0=$!
+waitudp4port $PORT 1
+$CMD1 >"${tf}1" 2>"${te}1"
+rc1=$?
+kill $pid0 2>/dev/null; wait
+if grep "$da" "${tf}0" >/dev/null; then
+    $PRINTF "$OK\n"
+    if [ "$VERBOSE" ]; then echo "$CMD0 &"; fi
+    if [ "$DEBUG" ];   then cat "${te}0" >&2; fi
+    if [ "$VERBOSE" ]; then echo "$CMD1"; fi
+    if [ "$DEBUG" ];   then cat "${te}1" >&2; fi
+    numOK=$((numOK+1))
+elif pgrep -u root nscd >/dev/null 2>&1; then
+    $PRINTF "${YELLOW}FAILED (due to nscd?)${NORMAL}\n"
+    if [ "$VERBOSE" ]; then echo "$CMD0 &"; fi
+    if [ "$DEBUG" ];   then cat "${te}0" >&2; fi
+    if [ "$VERBOSE" ]; then echo "$CMD1"; fi
+    if [ "$DEBUG" ];   then cat "${te}1" >&2; fi
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+    namesCAnT="$namesCANT $NAME"
+else
+    $PRINTF "$FAILED (query not received)\n"
+    echo "$CMD0 &"
+    cat "${te}0" >&2
+    echo "$CMD1"
+    cat "${te}1" >&2
+    numFAIL=$((numFAIL+1))
+    listFAIL="$listFAIL $N"
+    namesFAIL="$namesFAIL $NAME"
+fi
+fi # NUMCOND
+ ;;
+esac
+N=$((N+1))
+
+
 # end of common tests
 
 ##################################################################################
@@ -17502,6 +17576,7 @@ elif [ ??? ]; then
     if [ "$DEBUG" ];   then cat "${te}1" >&2; fi
     numCANT=$((numCANT+1))
     listCANT="$listCANT $N"
+    namesCANT="$namesCANT $NAME"
 else
     $PRINTF "$OK\n"
     if [ "$VERBOSE" ]; then echo "$CMD0 &"; fi

xio-ip.c

@@ -116,6 +116,9 @@ const struct optdesc opt_res_retrans  = { "res-retrans",  "retrans",  OPT_RES_RE
 #if HAVE_RES_RETRY
 const struct optdesc opt_res_retry    = { "res-retry",    NULL,       OPT_RES_RETRY,    GROUP_SOCK_IP, PH_OFFSET, TYPE_INT,  OFUNC_OFFSET,       XIO_OFFSETOF(para.socket.ip.res.retry),   XIO_SIZEOF(para.socket.ip.res.retry),   RES_MAXRETRY };
 #endif
+#if HAVE_RES_NSADDR_LIST
+const struct optdesc opt_res_nsaddr   = { "res-nsaddr",   "dns",      OPT_RES_NSADDR,   GROUP_SOCK_IP, PH_OFFSET, TYPE_IP4SOCK, OFUNC_OFFSET,    XIO_OFFSETOF(para.socket.ip.res.nsaddr),  XIO_SIZEOF(para.socket.ip.res.retry),   RES_MAXRETRY };
+#endif
 #endif /* HAVE_RESOLV_H */
 #endif /* WITH_RESOLVE */
 #endif /* WITH_IP4 || WITH_IP6 */
@@ -139,7 +142,9 @@ int xioinit_ip(
 	return 0;
 }
 
+
 #if HAVE_RESOLV_H
+
 int Res_init(void) {
    int result;
    Debug("res_init()");
@@ -147,13 +152,9 @@ int Res_init(void) {
    Debug1("res_init() -> %d", result);
    return result;
 }
+
 #endif /* HAVE_RESOLV_H */
 
-#if HAVE_RESOLV_H
-unsigned long res_opts() {
-   return _res.options;
-}
-#endif /* HAVE_RESOLV_H */
 
 /* the ultimate(?) socat resolver function
  node: the address to be resolved; supported forms:
@@ -1015,7 +1016,18 @@ int xio_res_init(
 	struct __res_state *save_res)
 {
 	if (sfd->para.socket.ip.res.opts[0] ||
-	    sfd->para.socket.ip.res.opts[1]) {
+	    sfd->para.socket.ip.res.opts[1] ||
+#if HAVE_RES_RETRANS
+	    sfd->para.socket.ip.res.retrans >= 0 ||
+#endif
+#if HAVE_RES_RETRY
+	    sfd->para.socket.ip.res.retry >= 0 ||
+#endif
+#if HAVE_RES_NSADDR_LIST
+	    sfd->para.socket.ip.res.nsaddr.sin_family != PF_UNSPEC ||
+#endif
+	    0 	/* for canonical reasons */
+		) {
 		if (!(_res.options & RES_INIT)) {
 			if (Res_init() < 0) {
 				Error("res_init() failed");
@@ -1027,8 +1039,44 @@ int xio_res_init(
 		_res.options &= ~sfd->para.socket.ip.res.opts[1];
 		Debug2("changed _res.options from 0x%lx to 0x%lx",
 		       save_res->options, _res.options);
+
+#if HAVE_RES_RETRANS
+		if (sfd->para.socket.ip.res.retrans >= 0) {
+			_res.retrans = sfd->para.socket.ip.res.retrans;
+			Debug2("changed _res.retrans from 0x%x to 0x%x",
+			       save_res->retrans, _res.retrans);
+		}
+#endif
+#if HAVE_RES_RETRY
+		if (sfd->para.socket.ip.res.retry >= 0) {
+			_res.retry = sfd->para.socket.ip.res.retry;
+			Debug2("changed _res.retry from 0x%x to 0x%x",
+			       save_res->retry, _res.retry);
+		}
+#endif
+#if HAVE_RES_NSADDR_LIST
+		if (sfd->para.socket.ip.res.nsaddr.sin_family == PF_INET) {
+			_res.nscount = 1;
+			_res.nsaddr_list[0] = sfd->para.socket.ip.res.nsaddr;
+			if (_res.nsaddr_list[0].sin_port == htons(0))
+				_res.nsaddr_list[0].sin_port = htons(53);
+			Debug10("changed _res.nsaddr_list[0] from %u.%u.%u.%u:%u to %u.%u.%u.%u:%u",
+				((unsigned char *)&save_res->nsaddr_list[0].sin_addr.s_addr)[0],
+				((unsigned char *)&save_res->nsaddr_list[0].sin_addr.s_addr)[1],
+				((unsigned char *)&save_res->nsaddr_list[0].sin_addr.s_addr)[2],
+				((unsigned char *)&save_res->nsaddr_list[0].sin_addr.s_addr)[3],
+				ntohs(save_res->nsaddr_list[0].sin_port),
+				((unsigned char *)&_res.nsaddr_list[0].sin_addr.s_addr)[0],
+				((unsigned char *)&_res.nsaddr_list[0].sin_addr.s_addr)[1],
+				((unsigned char *)&_res.nsaddr_list[0].sin_addr.s_addr)[2],
+				((unsigned char *)&_res.nsaddr_list[0].sin_addr.s_addr)[3],
+				ntohs(_res.nsaddr_list[0].sin_port));
+		}
+#endif /* HAVE_RES_NSADDR_LIST */
+
 		return 1;
 	}
+
 	return 0;
 }
 

xio-ip.h

@@ -44,6 +44,7 @@ extern const struct optdesc opt_res_stayopen;
 extern const struct optdesc opt_res_dnsrch;
 extern const struct optdesc opt_res_retrans;
 extern const struct optdesc opt_res_retry;
+extern const struct optdesc opt_res_nsaddr;
 
 extern int xioinit_ip(int *pf, char ipv);
 

xio.h

@@ -143,6 +143,10 @@ struct para_ip_res {
 #if HAVE_RES_RETRY
 	int	 retry;
 #endif
+#if HAVE_RES_NSADDR_LIST
+#	undef nsaddr 	/* resolv.h might define this, breaks debugger */
+	struct sockaddr_in nsaddr;
+#endif
 } ;
 #endif /* WITH_RESOLVE && HAVE_RESOLV_H */
 
@@ -423,6 +427,7 @@ union integral {
 #endif /* HAVE_STRUCT_TIMESPEC */
 #if WITH_IP4
    struct in_addr  u_ip4addr;
+   struct sockaddr_in  u_ip4sock;
 #endif
 } ;
 

xiohelp.c

@@ -22,7 +22,7 @@ static const char *optiontypenames[] = {
 	"OFF64_T",	"INT:INT",	"INT:INTP",	"INT:BIN",
 	"INT:STRING",	"INT:INT:INT",	"INT:INT:BIN",	"INT:INT:STRING",
 	"INT:INT:GENERIC",
-	"IP4NAME",
+	"IP4NAME",	"IP4SOCK",
 #if HAVE_STRUCT_LINGER
 			"STRUCT-LINGER",
 #endif

xioopts.c

@@ -430,6 +430,9 @@ const struct optname optionnames[] = {
 #ifdef VDISCARD
 	IF_TERMIOS("discard",	&opt_vdiscard)
 #endif
+#if HAVE_RES_NSADDR_LIST
+	IF_IP     ("dns",		&opt_res_nsaddr)
+#endif
 #if HAVE_RESOLV_H
 	IF_RESOLVE("dnsrch",		&opt_res_dnsrch)
 #endif /* HAVE_RESOLV_H */
@@ -1020,6 +1023,9 @@ const struct optname optionnames[] = {
 	IF_IP     ("multicast-ttl",	&opt_ip_multicast_ttl)
 	IF_IP     ("multicastloop",	&opt_ip_multicast_loop)
 	IF_IP     ("multicastttl",	&opt_ip_multicast_ttl)
+#if HAVE_RES_NSADDR_LIST
+	IF_IP     ("nameserver",	&opt_res_nsaddr)
+#endif
 #if defined(O_NDELAY) && (!defined(O_NONBLOCK) || O_NDELAY != O_NONBLOCK)
 	IF_ANY    ("ndelay",	&opt_o_ndelay)
 #else
@@ -1085,6 +1091,9 @@ const struct optname optionnames[] = {
 	IF_OPENSSL("nosni",		&opt_openssl_no_sni)
 #endif
 	IF_INTERFACE("notrailers",	&opt_iff_notrailers)
+#if HAVE_RES_NSADDR_LIST
+	IF_IP     ("nsaddr",		&opt_res_nsaddr)
+#endif
 #ifdef O_NSHARE
 	IF_OPEN   ("nshare",	&opt_o_nshare)
 #endif
@@ -1426,6 +1435,9 @@ const struct optname optionnames[] = {
 #  if HAVE_RES_RETRY
 	IF_RESOLVE("res-maxretry",	&opt_res_retry)
 #  endif
+#  if HAVE_RES_NSADDR_LIST
+	IF_IP     ("res-nsaddr",	&opt_res_nsaddr)
+#  endif
 #  if WITH_RES_PRIMARY
 	IF_RESOLVE("res-primary",	&opt_res_primary)
 #  endif
@@ -2630,6 +2642,7 @@ int parseopts_table(const char **a, groups_t groups, struct opt **opts,
 #if WITH_IP4
       case TYPE_IP4NAME:
 	 {
+	    /*! On a good day merge this with code in retropt_bind() */
 	    struct sockaddr_in sa;  socklen_t salen = sizeof(sa);
 	    const char *ends[] = { NULL };
 	    const char *nests[] = { "[","]", NULL };
@@ -2659,6 +2672,40 @@ int parseopts_table(const char **a, groups_t groups, struct opt **opts,
 	    opt->value.u_ip4addr = sa.sin_addr;
 	 }
 	 break;
+      case TYPE_IP4SOCK:
+	 {
+	    /*! On a good day merge this with code for TYPE_IP4NAME */
+	    struct sockaddr_in sa;  socklen_t salen = sizeof(sa);
+	    const char portsep[] = ":";
+	    const char *ends[] = { portsep, NULL };
+	    const char *nests[] = { "[","]", NULL };
+	    char hostname[512], *hostp = hostname, *portp = NULL;
+	    size_t hostlen = sizeof(hostname)-1;
+
+	    tokp = token;
+	    parsres =
+	    nestlex((const char **)&tokp, &hostp, &hostlen,
+		    ends, NULL, NULL, nests,
+		    true, false, false);
+	    if (parsres < 0) {
+	       Error1("option too long:  \"%s\"", *a);
+	       return -1;
+	    } else if (parsres > 0) {
+	       Error1("syntax error in \"%s\"", *a);
+	       return -1;
+	    }
+	    *hostp++ = '\0';
+	    if (!strncmp(tokp, portsep, strlen(portsep))) {
+	       portp = tokp + strlen(portsep);
+	    }
+	    if (xioresolve(hostname, portp, AF_INET, SOCK_DGRAM, IPPROTO_IP,
+			   (union sockaddr_union *)&sa, &salen, 0)
+		!= STAT_OK) {
+	       opt->desc = ODESC_ERROR; continue;
+	    }
+	    opt->value.u_ip4sock = sa;
+	 }
+	 break;
 #endif /* defined(WITH_IP4) */
 
 #if LATER
@@ -4132,6 +4179,15 @@ static int applyopt_offset(struct single *sfd, struct opt *opt) {
    case TYPE_CONST:
       *(int *)ptr = opt->desc->minor;
       break;
+   case TYPE_IP4NAME:
+      memset(ptr, 0, sizeof(struct sockaddr_in));
+      ((struct sockaddr_in *)ptr)->sin_addr   = opt->value.u_ip4addr;
+      ((struct sockaddr_in *)ptr)->sin_family = PF_INET;
+      break;
+   case TYPE_IP4SOCK:
+      memset(ptr, 0, sizeof(struct sockaddr_in));
+      *(struct sockaddr_in *)ptr = opt->value.u_ip4sock;
+      break;
    default:
       Error2("applyopt_offset(opt:%s): type %s not implemented",
 	     opt->desc->defname, xiohelp_opttypename(opt->desc->type));

xioopts.h

@@ -68,6 +68,7 @@ enum e_types {
    TYPE_INT_INT_GENERIC,	/* 3 params: first and second are int, 3rd is specified by value (dalan syntax) */
 
    TYPE_IP4NAME,	/* IPv4 hostname or address */
+   TYPE_IP4SOCK,	/* IPv4 hostname or address optionally with port */
 #if HAVE_STRUCT_LINGER
    TYPE_LINGER,		/* struct linger */
 #endif /* HAVE_STRUCT_LINGER */
@@ -628,6 +629,7 @@ enum e_optcode {
    OPT_RES_DEFNAMES,	/* resolver(3) */
    OPT_RES_DNSRCH,	/* resolver(3) */
    OPT_RES_IGNTC,	/* resolver(3) */
+   OPT_RES_NSADDR,	/* undocumented */
    OPT_RES_PRIMARY,	/* resolver(3) */
    OPT_RES_RECURSE,	/* resolver(3) */
    OPT_RES_RETRANS,	/* undocumented */