read rng seed from random number source device

Linux and BSD system have random number source devices that can be used
as source for a unguessable seed source.

Other platforms fall back to generate the seed with gettime().

include/extern.h

@@ -925,7 +925,8 @@ E char *FDECL(strstri, (const char *, const char *));
 #endif
 E boolean
 FDECL(fuzzymatch, (const char *, const char *, const char *, BOOLEAN_P));
-E void NDECL(setrandom);
+E void NDECL(init_random);
+E void NDECL(reseed_random);
 E time_t NDECL(getnow);
 E int NDECL(getyear);
 #if 0

include/unixconf.h

@@ -408,5 +408,18 @@
 # define RUNTIME_PASTEBUF_SUPPORT
 #endif
 
+/*
+ * /dev/random is blocking on Linux, so there we default to /dev/urandom which
+ * should still be good enough.
+ * BSD systems usually have /dev/random that is supposed to be used.
+ */
+#ifdef LINUX
+# define DEV_RANDOM "/dev/urandom"
+#else
+# ifdef BSD
+#  define DEV_RANDOM "/dev/random"
+# endif
+#endif
+
 #endif /* UNIXCONF_H */
 #endif /* UNIX */

src/hacklib.c

@@ -848,10 +848,21 @@ extern struct tm *FDECL(localtime, (time_t *));
 #endif
 STATIC_DCL struct tm *NDECL(getlt);
 
-void
+/* Returns a number suitable as seed for the random number generator. */
-setrandom()
+static unsigned long
+get_random_seed()
 {
-    unsigned long seed = (unsigned long) getnow(); /* time((TIME_type) 0) */
+    unsigned long seed = 0;
+#ifdef DEV_RANDOM
+    FILE *fptr = NULL;
+
+    fptr = fopen(DEV_RANDOM, "r");
+    if (fptr) {
+        fread(&seed, sizeof(long), 1, fptr);
+    }
+    fclose(fptr);
+#else
+    seed = (unsigned long) getnow(); /* time((TIME_type) 0) */
 
 # if defined(UNIX) || defined(VMS)
     {
@@ -865,7 +876,14 @@ setrandom()
         }
     }
 # endif
+#endif
+    return seed;
+}
 
+/* Sets the seed for the random number generator */
+static void
+set_random(unsigned long seed)
+{
     /* the types are different enough here that sweeping the different
      * routine names into one via #defines is even more confusing
      */
@@ -888,6 +906,17 @@ setrandom()
 #endif
 }
 
+/*
+ * Initializes the random number generator.
+ * Only call once.
+ */
+void
+init_random()
+{
+    unsigned long seed = get_random_seed();
+    set_random(seed);
+}
+
 time_t
 getnow()
 {

src/options.c

@@ -692,7 +692,7 @@ initoptions_init()
     reset_commands(TRUE); /* init */
 
     /* initialize the random number generator */
-    setrandom();
+    init_random();
 
     /* for detection of configfile options specified multiple times */
     iflags.opt_booldup = iflags.opt_compdup = (int *) 0;