[PATCH 09/18] net: use secure random for random MAC address

[Stephen Hemminger <stephen@networkplumber.org>]

rte_eth_random_addr() returned 48 bits of raw rte_rand() output on
every call. That both makes the generated address predictable and
leaks enough generator output to help recover the internal state.

Use rte_random_bytes() instead. The function cannot report an error
to its callers, so fall back to rte_rand() if the system random
generator is unavailable, which is no worse than the previous
behaviour.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/net/rte_ether.c | 13 ++++++++++---
 lib/net/rte_ether.h |  5 +++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/lib/net/rte_ether.c b/lib/net/rte_ether.c
index 6703145fc5..4b2932c00b 100644
--- a/lib/net/rte_ether.c
+++ b/lib/net/rte_ether.c
@@ -3,6 +3,7 @@
  */
 
 #include <stdbool.h>
+#include <string.h>
 
 #include <eal_export.h>
 #include <rte_ether.h>
@@ -12,10 +13,16 @@ RTE_EXPORT_SYMBOL(rte_eth_random_addr)
 void
 rte_eth_random_addr(uint8_t *addr)
 {
-	uint64_t rand = rte_rand();
-	uint8_t *p = (uint8_t *)&rand;
+	/* Prefer the system random generator so that the address can not
+	 * be predicted from other random values. Fall back to rte_rand()
+	 * if it is unavailable, which is what was always used before.
+	 */
+	if (rte_random_bytes(addr, RTE_ETHER_ADDR_LEN) != 0) {
+		uint64_t rand = rte_rand();
+
+		memcpy(addr, &rand, RTE_ETHER_ADDR_LEN);
+	}
 
-	rte_memcpy(addr, p, RTE_ETHER_ADDR_LEN);
 	addr[0] &= (uint8_t)~RTE_ETHER_GROUP_ADDR;	/* clear multicast bit */
 	addr[0] |= RTE_ETHER_LOCAL_ADMIN_ADDR;	/* set local assignment bit */
 }
diff --git a/lib/net/rte_ether.h b/lib/net/rte_ether.h
index c9a0b536c3..b0dc227362 100644
--- a/lib/net/rte_ether.h
+++ b/lib/net/rte_ether.h
@@ -221,6 +221,11 @@ static inline int rte_is_valid_assigned_ether_addr(const struct rte_ether_addr *
 /**
  * Generate a random Ethernet address that is locally administered
  * and not multicast.
+ *
+ * The address is taken from the random source of the operating system
+ * so that it cannot be predicted from other random values. If that
+ * source is unavailable it falls back to the pseudo-random rte_rand().
+ *
  * @param addr
  *   A pointer to Ethernet address.
  */
-- 
2.53.0