GUACAMOLE-1910: Add locking around TLS socket

When TLS is turned on the file descriptor for the socket does not use
locking when writing to it. It results in corrupted guacamole
instructions being written to the stream when there are multiple
connected clients.

This adds a mutex in the same manner done in `socket-fd.c`.

src/libguac/guacamole/socket-ssl.h

@@ -31,6 +31,7 @@
 #include "socket-types.h"
 
 #include <openssl/ssl.h>
+#include <pthread.h>
 
 /**
  * SSL socket-specific data.
@@ -54,6 +55,12 @@ typedef struct guac_socket_ssl_data {
      */
     SSL* ssl;
 
+    /**
+     * Lock that is acquired when an instruction is being written, and released
+     * when the instruction is finished being written.
+     */
+    pthread_mutex_t socket_lock;
+
 } guac_socket_ssl_data;
 
 /**

src/libguac/socket-ssl.c

@@ -25,6 +25,7 @@
 #include "guacamole/socket.h"
 #include "wait-fd.h"
 
+#include <pthread.h>
 #include <stdlib.h>
 
 #include <openssl/ssl.h>
@@ -97,10 +98,42 @@ static int __guac_socket_ssl_free_handler(guac_socket* socket) {
     /* Close file descriptor */
     close(data->fd);
 
+    pthread_mutex_destroy(&(data->socket_lock));
+
     guac_mem_free(data);
     return 0;
 }
 
+/**
+ * Acquires exclusive access to the given socket.
+ *
+ * @param socket
+ *      The guac_socket to which exclusive access is requested.
+ */
+static void __guac_socket_ssl_lock_handler(guac_socket* socket) {
+
+    guac_socket_ssl_data* data = (guac_socket_ssl_data*) socket->data;
+
+    /* Acquire exclusive access to the socket */
+    pthread_mutex_lock(&(data->socket_lock));
+
+}
+
+/**
+ * Releases exclusive access to the given socket.
+ *
+ * @param socket
+ *      The guac_socket to which exclusive access is released.
+ */
+static void __guac_socket_ssl_unlock_handler(guac_socket* socket) {
+
+    guac_socket_ssl_data* data = (guac_socket_ssl_data*) socket->data;
+
+    /* Relinquish exclusive access to the socket */
+    pthread_mutex_unlock(&(data->socket_lock));
+
+}
+
 guac_socket* guac_socket_open_secure(SSL_CTX* context, int fd) {
 
     /* Create new SSL structure */
@@ -129,6 +162,11 @@ guac_socket* guac_socket_open_secure(SSL_CTX* context, int fd) {
         return NULL;
     }
 
+    pthread_mutexattr_t lock_attributes;
+    pthread_mutexattr_init(&lock_attributes);
+    pthread_mutexattr_setpshared(&lock_attributes, PTHREAD_PROCESS_SHARED);
+    pthread_mutex_init(&(data->socket_lock), &lock_attributes);
+
     /* Store file descriptor as socket data */
     data->fd = fd;
     socket->data = data;
@@ -138,6 +176,8 @@ guac_socket* guac_socket_open_secure(SSL_CTX* context, int fd) {
     socket->write_handler  = __guac_socket_ssl_write_handler;
     socket->select_handler = __guac_socket_ssl_select_handler;
     socket->free_handler   = __guac_socket_ssl_free_handler;
+    socket->lock_handler   = __guac_socket_ssl_lock_handler;
+    socket->unlock_handler = __guac_socket_ssl_unlock_handler;
 
     return socket;