Return NULL if we fail to create a BIO in the demos/quicserver

Strictly speaking the previous code was still correct since BIO_set_fd
is tolerant of a NULL BIO. But this way is more clear.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from #21950)

demos/guide/quic-client-block.c

@@ -89,10 +89,12 @@ static BIO *create_socket_bio(const char *hostname, const char *port,
     if (sock == -1)
         return NULL;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_datagram());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

demos/guide/quic-client-non-block.c

@@ -90,10 +90,12 @@ static BIO *create_socket_bio(const char *hostname, const char *port,
     if (sock == -1)
         return NULL;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_datagram());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

demos/guide/quic-multi-stream.c

@@ -90,11 +90,12 @@ static BIO *create_socket_bio(const char *hostname, const char *port,
     if (sock == -1)
         return NULL;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_datagram());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
-
+        return NULL;
+    }
     /*
      * Associate the newly created BIO with the underlying socket. By
      * passing BIO_CLOSE here the socket will be automatically closed when

demos/guide/tls-client-block.c

@@ -76,8 +76,10 @@ static BIO *create_socket_bio(const char *hostname, const char *port)
 
     /* Create a BIO to wrap the socket*/
     bio = BIO_new(BIO_s_socket());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

demos/guide/tls-client-non-block.c

@@ -81,10 +81,12 @@ static BIO *create_socket_bio(const char *hostname, const char *port)
     if (sock == -1)
         return NULL;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_socket());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

doc/man7/ossl-guide-quic-client-block.pod

@@ -165,10 +165,12 @@ associate it with a BIO object:
 
     BIO *bio;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_datagram());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

doc/man7/ossl-guide-tls-client-block.pod

@@ -222,10 +222,12 @@ BIO object:
 
     BIO *bio;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_socket());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By

util/quicserver.c

@@ -113,10 +113,12 @@ static BIO *create_dgram_bio(int family, const char *hostname, const char *port)
     if (sock == -1)
         return NULL;
 
-    /* Create a BIO to wrap the socket*/
+    /* Create a BIO to wrap the socket */
     bio = BIO_new(BIO_s_datagram());
-    if (bio == NULL)
+    if (bio == NULL) {
         BIO_closesocket(sock);
+        return NULL;
+    }
 
     /*
      * Associate the newly created BIO with the underlying socket. By