netdev - Re: [net-next PATCH V2] etherdevice.h: random_ether

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Date:	Fri, 11 Sep 2009 13:44:22 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Miller <davem@...emloft.net>
Cc:	shemminger@...tta.com, jeffrey.t.kirsher@...el.com,
	netdev@...r.kernel.org, gospo@...hat.com, gregory.v.rose@...el.com,
	donald.c.skidmore@...el.com
Subject: Re: [net-next PATCH V2] etherdevice.h: random_ether_addr update

Perhaps this is slightly better, it doesn't call
random32 for each octet and makes sure the leading
octet is >= 0x04.

random_ether_address should assign a leading octet >= "0x04"

Does not use get_random_bytes to avoid drawing down entropy pool.

Signed-off-by: Joe Perches <joe@...ches.com>

diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
index 3d7a668..fddcabf 100644
--- a/include/linux/etherdevice.h
+++ b/include/linux/etherdevice.h
@@ -121,9 +121,26 @@ static inline int is_valid_ether_addr(const u8 *addr)
  */
 static inline void random_ether_addr(u8 *addr)
 {
-	get_random_bytes (addr, ETH_ALEN);
-	addr [0] &= 0xfe;	/* clear multicast bit */
-	addr [0] |= 0x02;	/* set local assignment bit (IEEE802) */
+	u32 val;
+
+	/* not calling get_random_bytes to avoid using entropy */
+	do {
+		val = random32();
+		addr[0] = val;
+	} while (addr[0] < 4);
+	addr[0] &= 0xfe;	/* clear multicast bit */
+	addr[0] |= 0x02;	/* set local assignment bit (IEEE802) */
+
+	val >>= 8;
+	addr[1] = val;
+	val >>= 8;
+	addr[2] = val;
+	val >>= 8;
+	addr[3] = val;
+	val = random32();
+	addr[4] = val;
+	val >>= 8;
+	addr[5] = val;
 }
 
 /**


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