When a DNS query is sent out, the ethernet packet can get directed to the MAC address of a server that was communicated to before. This is wrong when the previously stored MAC address corresponds to a different server's IP address, i.e. when the IP address of the previous and the current communication are different.

The error can get reproduced by running a sequence of e.g. a TFTP download and a DNS query, where the TFTP and DNS servers reside on individual machines.

The fix is to clear the server's MAC address that might be left from a previous operation, and to fetch the peer's MAC address in a new ARP lookup, before the DNS query is sent. This is the approach taken in other network services, like 8e52533d1095 ("net: tftpsrv: Get correct client MAC address").

Reported-by: Dirk Zimoch dirk.zimoch@psi.ch Signed-off-by: Gerhard Sittig gsi@denx.de ---

This patch suffers from a checkpatch warning about CamelCase, which cannot get resolved, as it is a consequence of established identifier names in the network part of the code base.

--- net/dns.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/net/dns.c b/net/dns.c index ff9ddffc9d0a..b667bdb528f7 100644 --- a/net/dns.c +++ b/net/dns.c @@ -199,8 +199,12 @@ DnsStart(void) { debug("%s\n", __func__);

+ /* Register handlers for incoming packets and timeouts. */ NetSetTimeout(DNS_TIMEOUT, DnsTimeout); net_set_udp_handler(DnsHandler);

+ /* Clear a previous MAC address, the server IP might have changed. */ + memset(NetServerEther, 0, sizeof(NetServerEther)); + DnsSend(); }