[PATCH 3/3] net: bootp: add config option BOOTP_RANDOM_XID

[seanedmond@linux.microsoft.com]

From: Sean Edmond <seanedmond@microsoft.com>

The new config option BOOTP_RANDOM_XID will randomize the transaction ID
for each new BOOT/DHCPv4 exchange.

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
---
 cmd/Kconfig |  7 +++++++
 net/bootp.c | 31 +++++++++++++++++--------------
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 25c1efc41e..4be5be8724 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1829,6 +1829,13 @@ config BOOTP_VCI_STRING
 	default "U-Boot.arm" if ARM
 	default "U-Boot"
 
+config BOOTP_RANDOM_XID
+	bool "Send random transaction ID to BOOTP/DHCP server"
+	depends on CMD_BOOTP
+	help
+	  Selecting this will allow for a random transaction ID to get
+	  selected for each BOOTP/DHCPv4 exchange.
+
 if CMD_DHCP6
 
 config DHCP6_PXE_CLIENTARCH
diff --git a/net/bootp.c b/net/bootp.c
index 7248536cc4..5053a1b870 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -832,22 +832,25 @@ void bootp_request(void)
 
 	/* Only generate a new transaction ID for each new BOOTP request */
 	if (bootp_try == 1) {
-		/*
-		 *	Bootp ID is the lower 4 bytes of our ethernet address
-		 *	plus the current time in ms.
-		 */
-		bootp_id = ((u32)net_ethaddr[2] << 24)
-			| ((u32)net_ethaddr[3] << 16)
-			| ((u32)net_ethaddr[4] << 8)
-			| (u32)net_ethaddr[5];
-		bootp_id += get_timer(0);
-		bootp_id = htonl(bootp_id);
-		bootp_add_id(bootp_id);
-		net_copy_u32(&bp->bp_id, &bootp_id);
-	} else {
-		net_copy_u32(&bp->bp_id, &bootp_id);
+		if (IS_ENABLED(CONFIG_BOOTP_RANDOM_XID)) {
+			srand(get_ticks() + rand());
+			bootp_id = rand();
+		} else {
+			/*
+			 *	Bootp ID is the lower 4 bytes of our ethernet address
+			 *	plus the current time in ms.
+			 */
+			bootp_id = ((u32)net_ethaddr[2] << 24)
+				| ((u32)net_ethaddr[3] << 16)
+				| ((u32)net_ethaddr[4] << 8)
+				| (u32)net_ethaddr[5];
+			bootp_id += get_timer(0);
+			bootp_id = htonl(bootp_id);
+		}
 	}
 
+	bootp_add_id(bootp_id);
+	net_copy_u32(&bp->bp_id, &bootp_id);
 	/*
 	 * Calculate proper packet lengths taking into account the
 	 * variable size of the options field
-- 
2.40.0