Open library file descriptors with O_CLOEXEC
This patch is non-portable, it needs linux 2.6.23 and glibc 2.7
or later, different combinations (old linux, new glibc and vice-versa)
will result in a crash.

To make it portable you have to test O_CLOEXEC support at *runtime*
compile time is not enough.


Index: curl-8.18.0/lib/file.c
===================================================================
--- curl-8.18.0.orig/lib/file.c
+++ curl-8.18.0/lib/file.c
@@ -258,7 +258,7 @@ static CURLcode file_connect(struct Curl
     }
   }
   #else
-  fd = curlx_open(real_path, O_RDONLY);
+  fd = curlx_open(real_path, O_RDONLY|O_CLOEXEC);
   file->path = real_path;
   #endif
 #endif
@@ -339,9 +339,9 @@ static CURLcode file_upload(struct Curl_
                   data->set.new_file_perms & (_S_IREAD | _S_IWRITE));
 #elif (defined(ANDROID) || defined(__ANDROID__)) && \
   (defined(__i386__) || defined(__arm__))
-  fd = curlx_open(file->path, mode, (mode_t)data->set.new_file_perms);
+  fd = curlx_open(file->path, mode|O_CLOEXEC, (mode_t)data->set.new_file_perms);
 #else
-  fd = curlx_open(file->path, mode, data->set.new_file_perms);
+  fd = curlx_open(file->path, mode|O_CLOEXEC, data->set.new_file_perms);
 #endif
   if(fd < 0) {
     failf(data, "cannot open %s for writing", file->path);
Index: curl-8.18.0/lib/if2ip.c
===================================================================
--- curl-8.18.0.orig/lib/if2ip.c
+++ curl-8.18.0/lib/if2ip.c
@@ -202,7 +202,7 @@ if2ip_result_t Curl_if2ip(int af,
   if(len >= sizeof(req.ifr_name))
     return IF2IP_NOT_FOUND;
 
-  dummy = CURL_SOCKET(AF_INET, SOCK_STREAM, 0);
+  dummy = CURL_SOCKET(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, 0);
   if(CURL_SOCKET_BAD == dummy)
     return IF2IP_NOT_FOUND;
 
Index: curl-8.18.0/configure.ac
===================================================================
--- curl-8.18.0.orig/configure.ac
+++ curl-8.18.0/configure.ac
@@ -504,6 +504,8 @@ AC_DEFINE_UNQUOTED(CURL_OS, "${host}", [
 # Silence warning: ar: 'u' modifier ignored since 'D' is the default
 AC_SUBST(AR_FLAGS, [cr])
 
+AC_USE_SYSTEM_EXTENSIONS
+
 dnl This defines _ALL_SOURCE for AIX
 CURL_CHECK_AIX_ALL_SOURCE
 
Index: curl-8.18.0/lib/hostip.c
===================================================================
--- curl-8.18.0.orig/lib/hostip.c
+++ curl-8.18.0/lib/hostip.c
@@ -43,6 +43,7 @@
 #include <setjmp.h>  /* for sigjmp_buf, sigsetjmp() */
 #include <signal.h>
 
+#include <fcntl.h>
 #include "urldata.h"
 #include "curl_trc.h"
 #include "connect.h"
@@ -689,7 +690,7 @@ bool Curl_ipv6works(struct Curl_easy *da
   else {
     int ipv6_works = -1;
     /* probe to see if we have a working IPv6 stack */
-    curl_socket_t s = CURL_SOCKET(PF_INET6, SOCK_DGRAM, 0);
+    curl_socket_t s = CURL_SOCKET(PF_INET6, SOCK_DGRAM|SOCK_CLOEXEC, 0);
     if(s == CURL_SOCKET_BAD)
       /* an IPv6 address was requested but we cannot get/use one */
       ipv6_works = 0;
Index: curl-8.18.0/lib/cf-socket.c
===================================================================
--- curl-8.18.0.orig/lib/cf-socket.c
+++ curl-8.18.0/lib/cf-socket.c
@@ -345,7 +345,8 @@ static CURLcode socket_open(struct Curl_
   }
   else {
     /* opensocket callback not set, so simply create the socket now */
-    *sockfd = CURL_SOCKET(addr->family, addr->socktype, addr->protocol);
+    *sockfd = CURL_SOCKET(addr->family, addr->socktype|SOCK_CLOEXEC,
+                          addr->protocol);
     if((*sockfd == CURL_SOCKET_BAD) && (SOCKERRNO == SOCKENOMEM))
       return CURLE_OUT_OF_MEMORY;
   }