Simon Kelley 7d5fbe7da3 Fix failure to add client MAC address to queries in TCP mode. ...

The options which cause dnsmasq to decorate a DNS query with the MAC
address on the originating client can fail when the query is sent
using TCP.

In TCP mode, dnsmasq spawns a new process to handle each TCP connection.
These child processes do not have an open netlink socket, which is
needed to read the kernel ARP table, so the process of adding the
client's MAC address as an EDNS0 option silently fails.

This is fixed by this patch by updating dnsmasq's ARP cache in the
main process just before forking the TCP-handler child process.
This ensures that the copy of the ARP cache inherited by the
TCP-handler contains the information required without the need to
read the kernel ARP table.

Thanks to Bruno Ravara for spotting and characterising this bug.

2025-11-26 21:54:59 +00:00

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