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-7.69.0/lib/file.c
===================================================================
--- curl-7.69.0.orig/lib/file.c
+++ curl-7.69.0/lib/file.c
@@ -192,7 +192,7 @@ static CURLcode file_connect(struct conn
     return CURLE_URL_MALFORMAT;
   }
 
-  fd = open_readonly(real_path, O_RDONLY);
+  fd = open_readonly(real_path, O_RDONLY|O_CLOEXEC);
   file->path = real_path;
 #endif
   file->freepath = real_path; /* free this when done */
@@ -285,7 +285,7 @@ static CURLcode file_upload(struct conne
   else
     mode = MODE_DEFAULT|O_TRUNC;
 
-  fd = open(file->path, mode, conn->data->set.new_file_perms);
+  fd = open(file->path, mode | O_CLOEXEC, conn->data->set.new_file_perms);
   if(fd < 0) {
     failf(data, "Can't open %s for writing", file->path);
     return CURLE_WRITE_ERROR;
Index: curl-7.69.0/lib/hostip6.c
===================================================================
--- curl-7.69.0.orig/lib/hostip6.c
+++ curl-7.69.0/lib/hostip6.c
@@ -44,7 +44,7 @@
 #ifdef HAVE_PROCESS_H
 #include <process.h>
 #endif
-
+#include <fcntl.h>
 #include "urldata.h"
 #include "sendf.h"
 #include "hostip.h"
@@ -76,7 +76,7 @@ bool Curl_ipv6works(struct connectdata *
   else {
     int ipv6_works = -1;
     /* probe to see if we have a working IPv6 stack */
-    curl_socket_t s = socket(PF_INET6, SOCK_DGRAM, 0);
+    curl_socket_t s = socket(PF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, 0);
     if(s == CURL_SOCKET_BAD)
       /* an IPv6 address was requested but we can't get/use one */
       ipv6_works = 0;
Index: curl-7.69.0/lib/if2ip.c
===================================================================
--- curl-7.69.0.orig/lib/if2ip.c
+++ curl-7.69.0/lib/if2ip.c
@@ -201,7 +201,7 @@ if2ip_result_t Curl_if2ip(int af, unsign
   if(len >= sizeof(req.ifr_name))
     return IF2IP_NOT_FOUND;
 
-  dummy = socket(AF_INET, SOCK_STREAM, 0);
+  dummy = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
   if(CURL_SOCKET_BAD == dummy)
     return IF2IP_NOT_FOUND;
 
Index: curl-7.69.0/lib/connect.c
===================================================================
--- curl-7.69.0.orig/lib/connect.c
+++ curl-7.69.0/lib/connect.c
@@ -1529,7 +1529,7 @@ CURLcode Curl_socket(struct connectdata
   }
   else
     /* opensocket callback not set, so simply create the socket now */
-    *sockfd = socket(addr->family, addr->socktype, addr->protocol);
+    *sockfd = socket(addr->family, addr->socktype | SOCK_CLOEXEC, addr->protocol);
 
   if(*sockfd == CURL_SOCKET_BAD)
     /* no socket, no connection */
Index: curl-7.69.0/configure.ac
===================================================================
--- curl-7.69.0.orig/configure.ac
+++ curl-7.69.0/configure.ac
@@ -196,6 +196,8 @@ AC_DEFINE_UNQUOTED(OS, "${host}", [cpu-m
 # 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