[PATCH] (4/4) use system get_random_bytes in hdlcdrv

[PATCH] (4/4) use system get_random_bytes in hdlcdrv

[Stephen Hemminger]

Real random numbers aren't important here, but having custom
random number generate seems silly when linux kernel has good
way to get random data.

diff -Nru a/drivers/net/hamradio/hdlcdrv.c b/drivers/net/hamradio/hdlcdrv.c
--- a/drivers/net/hamradio/hdlcdrv.c	Fri Sep 19 13:18:58 2003
+++ b/drivers/net/hamradio/hdlcdrv.c	Fri Sep 19 13:18:58 2003
@@ -52,6 +52,7 @@
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/init.h>
+#include <linux/random.h>
 #include <asm/bitops.h>
 #include <asm/uaccess.h>
 
@@ -434,18 +435,10 @@
 
 /* ---------------------------------------------------------------------- */
 
-static unsigned short random_seed;
-
-static inline unsigned short random_num(void)
-{
-	random_seed = 28629 * random_seed + 157;
-	return random_seed;
-}
-
-/* ---------------------------------------------------------------------- */
-
 void hdlcdrv_arbitrate(struct net_device *dev, struct hdlcdrv_state *s)
 {
+	u8 prand;
+
 	if (!s || s->magic != HDLCDRV_MAGIC || s->hdlctx.ptt || !s->skb) 
 		return;
 	if (s->ch_params.fulldup) {
@@ -459,7 +452,9 @@
 	if ((--s->hdlctx.slotcnt) > 0)
 		return;
 	s->hdlctx.slotcnt = s->ch_params.slottime;
-	if ((random_num() % 256) > s->ch_params.ppersist)
+
+	get_random_bytes(&prand, sizeof(prand));
+	if (prand > s->ch_params.ppersist)
 		return;
 	start_tx(dev, s);
 }

Re: [PATCH] (4/4) use system get_random_bytes in hdlcdrv

[Andi Kleen]

>  void hdlcdrv_arbitrate(struct net_device *dev, struct hdlcdrv_state *s)
>  {
> +	u8 prand;
> +
>  	if (!s || s->magic != HDLCDRV_MAGIC || s->hdlctx.ptt || !s->skb) 
>  		return;
>  	if (s->ch_params.fulldup) {
> @@ -459,7 +452,9 @@
>  	if ((--s->hdlctx.slotcnt) > 0)
>  		return;
>  	s->hdlctx.slotcnt = s->ch_params.slottime;
> -	if ((random_num() % 256) > s->ch_params.ppersist)
> +
> +	get_random_bytes(&prand, sizeof(prand));
> +	if (prand > s->ch_params.ppersist)

The "hard" random numbers generated by get_random_bytes
are a precious scarce resource (many systems don't generate them very often).
They should only be used as seed or when it is needed for security, otherwise
users who really need them risk blocking on /dev/random.
Especially if that function is called often it would be a bad idea.

-Andi

Re: [PATCH] (4/4) use system get_random_bytes in hdlcdrv

[Stephen Hemminger]

On Fri, 19 Sep 2003 23:46:42 +0200
Andi Kleen <ak@suse.de> wrote:

> >  void hdlcdrv_arbitrate(struct net_device *dev, struct hdlcdrv_state *s)
> >  {
> > +	u8 prand;
> > +
> >  	if (!s || s->magic != HDLCDRV_MAGIC || s->hdlctx.ptt || !s->skb) 
> >  		return;
> >  	if (s->ch_params.fulldup) {
> > @@ -459,7 +452,9 @@
> >  	if ((--s->hdlctx.slotcnt) > 0)
> >  		return;
> >  	s->hdlctx.slotcnt = s->ch_params.slottime;
> > -	if ((random_num() % 256) > s->ch_params.ppersist)
> > +
> > +	get_random_bytes(&prand, sizeof(prand));
> > +	if (prand > s->ch_params.ppersist)
> 
> The "hard" random numbers generated by get_random_bytes
> are a precious scarce resource (many systems don't generate them very often).
> They should only be used as seed or when it is needed for security, otherwise
> users who really need them risk blocking on /dev/random.
> Especially if that function is called often it would be a bad idea.

Well go ahead an leave it out.  It gets called once, and isn't important.