[Dnsmasq-discuss] dnsmasq sending truncated DHCPv6 packets
Simon Kelley
simon at thekelleys.org.uk
Tue Dec 3 18:21:55 GMT 2019
On 03/12/2019 18:16, Simon Kelley wrote:
> Ignore previous suggestions, I think I see the problem.
>
> The code to send a packet is
>
> while (retry_send(sendto(daemon->dhcp6fd, daemon->outpacket.iov_base,
> save_counter(0), 0, (struct sockaddr *)&from,
> sizeof(from))));
>
>
> where the length to send comes from the call to save_counter(0), which
> does two things: 1) it returns the length of the packet in the buffer,
> and 2) it zeros the length of the packet in the packet buffer.
>
> 99% of the time, the while() loop will only execute once, and this will
> be fine. If the syscall gets interrupted, the while loop executes a
> second time and a zero-length packet gets sent.
>
> The patch to fix this is trivial: change the save_counter() call to
>
> save_counter(-1)
>
> I just checked, and this mistake only occurs here, and has been there
> since forever.
>
> Good spot.
>
> Simon.
>
Patch committed:
http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=f73f7397d7e99f8412b7dc465061d20f642cdc85
Simon.
More information about the Dnsmasq-discuss
mailing list