[PATCH] net: Do not respond to ICMP_ECHO_REQUEST if we do not have an IP address

[Tom Rini]

On Sat, Nov 14, 2020 at 10:12:47PM -0500, David Rivshin wrote:

> From: David Rivshin <DRivshin at allworx.com>
> 
> While doing DHCP the interface IP is set to 0.0.0.0. This causes the
> check in net.c on dst_ip to be effectively skipped, and all IP datagrams
> are accepted up the IP stack. In the case of an ICMP_ECHO_REQUEST for the
> matching MAC address (regardless of destination IP), the result is that
> an ICMP_ECHO_REPLY is sent. The source address of the ICMP_ECHO_REPLY is
> 0.0.0.0, which is an illegal source address.
> 
> This can happen in common practice with the following sequence:
> DHCP (U-Boot or OS) acquires IP address 10.0.0.1
> System reboots
> U-Boot starts DHCP and send DHCP DISCOVER
> DHCP server decides to OFFER 10.0.0.1 again
>   (perhaps because of existing lease or manual configuration)
> DHCP server tries to PING 10.0.0.1 to see if anyone is squatting on it
> DHCP server still has our MAC address in its ARP table for 10.0.0.1
> U-Boot receives PING, and responds with an illegal source address
> This may further result in a the DHCP server seeing the response as
>   confirmation that someone is squatting on 10.0.0.1, and picking a
>   new IP address from the pool to try again
> 
> Signed-off-by: David Rivshin <drivshin at allworx.com>

Applied to u-boot/master, thanks!

-- 
Tom
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