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From: David Schultz <das@FreeBSD.org>
Date: Mon, 16 Jan 2012 20:18:10 +0000 (UTC)
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Subject: svn commit: r230230 - head/sys/dev/random
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Author: das
Date: Mon Jan 16 20:18:10 2012
New Revision: 230230
URL: http://svn.freebsd.org/changeset/base/230230

Log:
  Generate a warning if the kernel's arc4random() is seeded with bogus entropy.

Modified:
  head/sys/dev/random/harvest.c

Modified: head/sys/dev/random/harvest.c
==============================================================================
--- head/sys/dev/random/harvest.c	Mon Jan 16 20:17:51 2012	(r230229)
+++ head/sys/dev/random/harvest.c	Mon Jan 16 20:18:10 2012	(r230230)
@@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/queue.h>
 #include <sys/random.h>
 #include <sys/selinfo.h>
+#include <sys/syslog.h>
 #include <sys/systm.h>
 #include <sys/sysctl.h>
 
@@ -48,6 +49,7 @@ static int read_random_phony(void *, int
 
 /* Structure holding the desired entropy sources */
 struct harvest_select harvest = { 1, 1, 1, 0 };
+static int warned = 0;
 
 /* hold the address of the routine which is actually called if
  * the randomdev is loaded
@@ -71,6 +73,7 @@ random_yarrow_deinit_harvester(void)
 {
 	reap_func = NULL;
 	read_func = read_random_phony;
+	warned = 0;
 }
 
 /* Entropy harvesting routine. This is supposed to be fast; do
@@ -108,6 +111,11 @@ read_random_phony(void *buf, int count)
 	u_long randval;
 	int size, i;
 
+	if (!warned) {
+		log(LOG_WARNING, "random device not loaded; using insecure entropy\n");
+		warned = 1;
+	}
+
 	/* srandom() is called in kern/init_main.c:proc0_post() */
 
 	/* Fill buf[] with random(9) output */