From 0a513555561d8ee4c1de930996ecc0cf73154378 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Sat, 5 Jun 2021 12:57:28 +0200
Subject: [PATCH] Revert "Revert "socketpair: fix potential hangs""

This reverts commit 3e70c3430a370a31eff2c1d8fea29edaca8f1127.

Thus brings back the change from #7144 as was originally landed in
c769d1eab4de8b

Closes #7144 (again)
---
 lib/socketpair.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/lib/socketpair.c b/lib/socketpair.c
index 2c580ad2d..26e1dc66d 100644
--- a/lib/socketpair.c
+++ b/lib/socketpair.c
@@ -48,6 +48,10 @@
 #endif /* !INADDR_LOOPBACK */
 #endif /* !WIN32 */
 
+#include "nonblock.h" /* for curlx_nonblock */
+#include "timeval.h"  /* needed before select.h */
+#include "select.h"   /* for Curl_poll */
+
 /* The last 3 #include files should be in this order */
 #include "curl_printf.h"
 #include "curl_memory.h"
@@ -59,12 +63,11 @@ int Curl_socketpair(int domain, int type, int protocol,
   union {
     struct sockaddr_in inaddr;
     struct sockaddr addr;
-  } a;
+  } a, a2;
   curl_socket_t listener;
   curl_socklen_t addrlen = sizeof(a.inaddr);
   int reuse = 1;
-  char data[2][12];
-  ssize_t dlen;
+  struct pollfd pfd[1];
   (void)domain;
   (void)type;
   (void)protocol;
@@ -85,7 +88,8 @@ int Curl_socketpair(int domain, int type, int protocol,
     goto error;
   if(bind(listener, &a.addr, sizeof(a.inaddr)) == -1)
     goto error;
-  if(getsockname(listener, &a.addr, &addrlen) == -1)
+  if(getsockname(listener, &a.addr, &addrlen) == -1 ||
+     addrlen < (int)sizeof(a.inaddr))
     goto error;
   if(listen(listener, 1) == -1)
     goto error;
@@ -94,18 +98,30 @@ int Curl_socketpair(int domain, int type, int protocol,
     goto error;
   if(connect(socks[0], &a.addr, sizeof(a.inaddr)) == -1)
     goto error;
+
+  /* use non-blocking accept to make sure we don't block forever */
+  if(curlx_nonblock(listener, TRUE) < 0)
+    goto error;
+  pfd[0].fd = listener;
+  pfd[0].events = POLLIN;
+  pfd[0].revents = 0;
+  (void)Curl_poll(pfd, 1, 10*1000); /* 10 seconds */
   socks[1] = accept(listener, NULL, NULL);
   if(socks[1] == CURL_SOCKET_BAD)
     goto error;
 
   /* verify that nothing else connected */
-  msnprintf(data[0], sizeof(data[0]), "%p", socks);
-  dlen = strlen(data[0]);
-  if(swrite(socks[0], data[0], dlen) != dlen)
+  addrlen = sizeof(a.inaddr);
+  if(getsockname(socks[0], &a.addr, &addrlen) == -1 ||
+     addrlen < (int)sizeof(a.inaddr))
     goto error;
-  if(sread(socks[1], data[1], sizeof(data[1])) != dlen)
+  addrlen = sizeof(a2.inaddr);
+  if(getpeername(socks[1], &a2.addr, &addrlen) == -1 ||
+     addrlen < (int)sizeof(a2.inaddr))
     goto error;
-  if(memcmp(data[0], data[1], dlen))
+  if(a.inaddr.sin_family != a2.inaddr.sin_family ||
+     a.inaddr.sin_addr.s_addr != a2.inaddr.sin_addr.s_addr ||
+     a.inaddr.sin_port != a2.inaddr.sin_port)
     goto error;
 
   sclose(listener);