From 5c1ea1fcd01c9be610c82e8f554edbc2456493e1 Mon Sep 17 00:00:00 2001
From: Ed Maste <emaste@FreeBSD.org>
Date: Mon, 3 Oct 2016 13:12:44 +0000
Subject: [PATCH] libc arc4_stir: use only kern.arandom sysctl

The sysctl cannot fail. If it does fail on some FreeBSD derivative or
after some future change, just abort() so that the problem will be found
and fixed.

It's preferable to provide an arc4random() function that cannot fail and
cannot return poor quality random data. While abort() is not normally
suitable for a library, it makes sense here.

Reviewed by:	ed, jonathan, markm
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D8077
---
 lib/libc/gen/arc4random.c | 28 +++++-----------------------
 1 file changed, 5 insertions(+), 23 deletions(-)

diff --git a/lib/libc/gen/arc4random.c b/lib/libc/gen/arc4random.c
index a22e290006f5..0fa3dff75cc9 100644
--- a/lib/libc/gen/arc4random.c
+++ b/lib/libc/gen/arc4random.c
@@ -137,35 +137,17 @@ arc4_sysctl(u_char *buf, size_t size)
 static void
 arc4_stir(void)
 {
-	int done, fd, i;
-	struct {
-		struct timeval	tv;
-		pid_t		pid;
-		u_char	 	rnd[KEYSIZE];
-	} rdat;
+	u_char rdat[KEYSIZE];
+	int i;
 
 	if (!rs_initialized) {
 		arc4_init();
 		rs_initialized = 1;
 	}
-	done = 0;
-	if (arc4_sysctl((u_char *)&rdat, KEYSIZE) == KEYSIZE)
-		done = 1;
-	if (!done) {
-		fd = _open(RANDOMDEV, O_RDONLY | O_CLOEXEC, 0);
-		if (fd >= 0) {
-			if (_read(fd, &rdat, KEYSIZE) == KEYSIZE)
-				done = 1;
-			(void)_close(fd);
-		}
-	}
-	if (!done) {
-		(void)gettimeofday(&rdat.tv, NULL);
-		rdat.pid = getpid();
-		/* We'll just take whatever was on the stack too... */
-	}
+	if (arc4_sysctl(rdat, KEYSIZE) != KEYSIZE)
+		abort(); /* Random sysctl cannot fail. */
 
-	arc4_addrandom((u_char *)&rdat, KEYSIZE);
+	arc4_addrandom(rdat, KEYSIZE);
 
 	/*
 	 * Discard early keystream, as per recommendations in: