Add FIPS mode detection

On FIPS-based systems, DES3 is not used at all, and the default
session type is UDS-based Xvnc rather than TCP-based Xvnc.

common/os_calls.c

@@ -4282,6 +4282,29 @@ g_no_new_privs(void)
 #endif
 }
 
+
+/*****************************************************************************/
+int
+g_fips_mode_enabled(void)
+{
+    int rv = 0;
+#if defined (__linux)
+    char buff[16];
+    int fd = open("/proc/sys/crypto/fips_enabled", O_RDONLY);
+
+    if (fd >= 0)
+    {
+        if (read(fd, buff, sizeof(buff)) > 0)
+        {
+            rv = (buff[0] != '0');
+        }
+
+        close(fd);
+    }
+#endif
+    return rv;
+}
+
 /*****************************************************************************/
 void
 g_qsort(void *base, size_t nitems, size_t size,

common/os_calls.h

@@ -428,6 +428,14 @@ int      g_tcp4_bind_address(int sck, const char *port, const char *address);
 int      g_tcp6_socket(void);
 int      g_tcp6_bind_address(int sck, const char *port, const char *address);
 int      g_no_new_privs(void);
+/**
+ * Query whether FIPS mode is enabled
+ *
+ * In FIPS mode, some cryptographic algorithms are disabled
+ *
+ * @return 1 -> FIPS mode enabled, 0 -> FIPS mode disabled or unknown
+ */
+int      g_fips_mode_enabled(void);
 void
 g_qsort(void *base, size_t nitems, size_t size,
         int (*compar)(const void *, const void *));
@@ -461,7 +469,7 @@ g_malloc_nofail(size_t size);
 
 /** Allocate memory with error-checking
  *
- * @param Number of elementst to allocate
+ * @param Number of elements to allocate
  * @param size Size of each element
  * @return Allocated memory
  *