svn commit: r230230 - head/sys/dev/random

[Andrey Chernov]

On Fri, Jan 20, 2012 at 03:12:53PM +0000, Mark Murray wrote:
> Andrey Chernov writes:
> > > Look at the function random_yarrow_unblock(). Thats where yopu want to
> > > be doing this. This function is where the random device is unblocked
> > > once safely seeded.
> > 
> > Thanx for your hint, but I fear one moment using random_yarrow_unblock().
> > It is called under mtx_lock(&random_reseed_mtx) in reseed().
> > And when arc4rand() seeding is called, it uses read_random(), so I see 
> > possible deadlock can happens.
> 
> The usual way round this is with a flag. Set a static, volatile flag, defaulting
> "off", and set it to "on" when the seeding has happened. Then arc4random() can
> do the right thing, depending on this flag.

Ok, what about this version, is it right? libkern/arc4rand.c is not 
a module but always present in the kernel, so "arc4rand_iniseed_state" will be 
always accessible.

--- dev/random/randomdev_soft.c.old	2011-09-26 07:35:48.000000000 +0400
+++ dev/random/randomdev_soft.c	2012-01-21 01:41:37.000000000 +0400
@@ -55,6 +55,8 @@ __FBSDID("$FreeBSD: src/sys/dev/random/r
 
 #define RANDOM_FIFO_MAX	256	/* How many events to queue up */
 
+extern int arc4rand_iniseed_state;
+
 static void random_kthread(void *);
 static void
 random_harvest_internal(u_int64_t, const void *, u_int,
@@ -361,6 +363,8 @@ random_yarrow_write(void *buf, int count
 void
 random_yarrow_unblock(void)
 {
+	if (arc4rand_iniseed_state == 0)
+		arc4rand_iniseed_state = 1;
 	if (!random_systat.seeded) {
 		random_systat.seeded = 1;
 		selwakeuppri(&random_systat.rsel, PUSER);
--- libkern/arc4random.c.old	2011-09-26 07:37:23.000000000 +0400
+++ libkern/arc4random.c	2012-01-21 01:46:53.000000000 +0400
@@ -24,6 +24,8 @@ __FBSDID("$FreeBSD: src/sys/libkern/arc4
 #define	ARC4_RESEED_SECONDS 300
 #define	ARC4_KEYBYTES (256 / 8)
 
+int arc4rand_iniseed_state = 0;
+
 static u_int8_t arc4_i, arc4_j;
 static int arc4_numruns = 0;
 static u_int8_t arc4_sbox[256];
@@ -130,10 +132,13 @@ arc4rand(void *ptr, u_int len, int resee
 	struct timeval tv;
 
 	getmicrouptime(&tv);
-	if (reseed || 
+	if (reseed || arc4rand_iniseed_state == 1 ||
 	   (arc4_numruns > ARC4_RESEED_BYTES) ||
-	   (tv.tv_sec > arc4_t_reseed))
+	   (tv.tv_sec > arc4_t_reseed)) {
+		if (arc4rand_iniseed_state == 1)
+			arc4rand_iniseed_state = -1;
 		arc4_randomstir();
+	}
 
 	mtx_lock(&arc4_mtx);
 	arc4_numruns += len;

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