README: add some useful links for leak checks

without -Werror=implicit-function-declaration our test for GNU-style
getservbyname_r silently succeeds on NetBSD 10
(because the function exists, so the testcase links successfully).

however NetBSD's version has a completely different signature which
leads to crashes at runtime:

    Program terminated with signal SIGSEGV, Segmentation fault.
    #0  0x0000f1707faa2b78 in free () from /usr/lib/libc.so.12
    [Current thread is 1 (process 25072)]
    (gdb) backtrace
    #0  0x0000f1707faa2b78 in free () from /usr/lib/libc.so.12
    #1  0x0000f1707fac58b0 in _servent_open () from /usr/lib/libc.so.12
    #2  0x0000f1707fac5a60 in setservent_r () from /usr/lib/libc.so.12
    #3  0x0000f1707fac4490 in getservbyname_r () from /usr/lib/libc.so.12
    #4  0x0000f17080235788 in mygetservbyname_r (name=0xf1707f847ab0 "80", proto=0x0, result_buf=0xffffffe29738, buf=0xffffffe29338 "", buflen=1024, result=0xffffffe29758) at src/core.c:917
    #5  0x0000f17080235aa8 in proxy_getaddrinfo (node=0xf1707f847ba0 "4get.nadeko.net", service=0xf1707f847ab0 "80", hints=0xffffffe29978, res=0xffffffe29968) at src/core.c:1004
    #6  0x0000f17080238a94 in getaddrinfo (node=0xf1707f847ba0 "4get.nadeko.net", service=0xf1707f847ab0 "80", hints=0xffffffe29978, res=0xffffffe29968) at src/libproxychains.c:795

netbsd's signature is:
struct servent *
getservbyname_r(const char *name, const char *proto, struct servent *sp,
    struct servent_data *sd)

and basically the first thing it does is to free existing members of the
sd struct, which obviously crashes when the thing passed as 4th argument
isn't actually that kind of struct.

README

@@ -263,6 +263,15 @@ Known Problems:
   there are unconfirmed reports that it works as root though.
   musl libc is unaffected from the bug.
 
+Useful links
+------------
+the following sites may prove useful to check for leaks:
+https://ipfighter.com/
+https://browserleaks.com/webrtc
+https://dnsleaktest.com
+http://check.torproject.org - tor specific
+http://ifconfig.me - can be used via curl
+http://ifconfig.io/
 
 Community:
 ----------

configure

@@ -182,6 +182,7 @@ ishaiku() {
 check_compile 'whether C compiler works' '' 'int main() {return 0;}' || fail 'error: install a C compiler and library'
 check_compile 'whether libc headers are complete' '' '#include <netdb.h>\nint main() {return 0;}' || fail 'error: necessary libc headers are not installed'
 check_compile 'whether C compiler understands -Wno-unknown-pragmas' '-Wno-unknown-pragmas' 'int main() {return 0;}'
+check_compile 'whether C compiler understands -Werror=implicit-function-declaration' '-Werror=implicit-function-declaration' 'int main() {return 0;}'
 
 if ! check_compile 'whether getnameinfo() servlen argument is POSIX compliant (socklen_t)' "-DGN_NODELEN_T=socklen_t -DGN_SERVLEN_T=socklen_t -DGN_FLAGS_T=int" \
 '#define _GNU_SOURCE\n#include <netdb.h>\nint getnameinfo(const struct sockaddr *, socklen_t, char *, socklen_t, char *, socklen_t, int);int main() {\nreturn 0;}' ; then
@@ -220,6 +221,7 @@ check_define __APPLE__ && {
 	fi
 }
 check_define __FreeBSD__ && bsd_detected=true
+check_define __NetBSD__ && bsd_detected=true
 check_define __OpenBSD__ && {
 bsd_detected=true
 echo "CFLAGS+=-DIS_OPENBSD">>config.mak
@@ -249,7 +251,7 @@ check_link "whether we can use -Wl,--no-as-needed" "-Wl,--no-as-needed" \
 LD_SONAME_FLAG=
 printf "checking what's the option to use in linker to set library name ... "
 for o in --soname -h -soname -install_name; do
-	check_link_silent "-shared -Wl,$o,libconftest.so" "void test_func(int a) {}" && LD_SONAME_FLAG=$o && break
+	check_link_silent "-shared -Wl,$o,libconftest.so" "void test_func(void) {}" && LD_SONAME_FLAG=$o && break
 done
 if [ -z "$LD_SONAME_FLAG" ]; then
 	printf '\ncannot find an option to set library name\n'

src/core.c

@@ -999,7 +999,7 @@ err_nn:
 	} else if(!node && !(hints->ai_flags & AI_PASSIVE)) {
 		af = ((struct sockaddr_in *) &space->sockaddr_space)->sin_family = AF_INET;
 		memcpy(&((struct sockaddr_in *) &space->sockaddr_space)->sin_addr,
-		       (char[]){127,0,0,1}, 4);
+		       "\177\0\0\1", 4);
 	}
 	if(service) mygetservbyname_r(service, NULL, &se_buf, buf, sizeof(buf), &se);
 

src/daemon/daemon.c

@@ -5,6 +5,7 @@
 
 */
 
+#undef _GNU_SOURCE
 #define _GNU_SOURCE
 #include <unistd.h>
 #define _POSIX_C_SOURCE 200809L

src/libproxychains.c

@@ -241,7 +241,7 @@ static int proxy_from_string(const char *proxystring,
 		ul = p-u;
 		p++;
 		pl = at-p;
-		if(proxytype == RS_PT_SOCKS5 && (ul > 255 || pl > 255))
+		if(ul > 255 || pl > 255)
 			return 0;
 		memcpy(user_buf, u, ul);
 		user_buf[ul]=0;
@@ -767,7 +767,7 @@ HOOKFUNC(int, connect, int sock, const struct sockaddr *addr, unsigned int len)
 }
 
 #ifdef IS_SOLARIS
-HOOKFUNC(int, __xnet_connect, int sock, const struct sockaddr *addr, unsigned int len)
+HOOKFUNC(int, __xnet_connect, int sock, const struct sockaddr *addr, unsigned int len) {
 	return connect(sock, addr, len);
 }
 #endif