PROXY UDP

[bAndie91]

would it work for UDP?

tested with netcat -u, and it made the client send the PROXY header corretly, but not the server.
obviously, because there is no accept() for udp.
i started to override recv*() family, but don´t know how coprehensive would it be.

my use-case is to make powerDNS authoritative server know the real source when curveDNS being the frontend for DNS requests and it forwards to powerDNS.

[msantos]

Hi @bAndie91 ! Thanks for opening an issue!

UDP is currently not supported:

libproxyproto/libproxyproto.c

Line 317 in f86c7ad

case 0x11: /* TCPv4 */

The protocol bytes are 0x12 for UDPv4 and 0x22 for UDPv6.

nc -u works because netcat uses a connected UDP socket. Intercepting sendto(2) and recvfrom(2) should cover most UDP usage.

A PR is welcome, otherwise I will look at adding support!

[bAndie91]

hi @msantos, thanks picking up the line.
if i understand well, need to patch these places:

• read_evt() - PROXYv2
  the respective address lengths are the same as for TCP so the structs for TCPv4 (((struct sockaddr_in *)from)->sin_addr.s_addr) and TCPv6 are good for UDP as well. maybe a case fall-through would be enough here?
• read_evt() - PROXYv1
  it fills in the same structs, so a pair of strcmp(token, "UDP4") and strcmp(token, "UDP6") would make it?
• implement recvfrom()
  as first glance, the problem is that it does not know how much is read from the socket. do we need to somehow note whether or not PROXY header is read from the socket?
• implement sendto()

[bAndie91]

i started to implement it here
https://github.com/msantos/libproxyproto/compare/master...bAndie91:libproxyproto:proxy-udp?expand=1
currently it does not seem to intercept recvfrom()…

[bAndie91]

it reads using recvmsg(). [EDIT] source address is in struct msghdr in msg_name field.

[bAndie91]

now it seems intercepting recvmsg is not enough, because the program understandably wants to reply to the faked (proxy) address. thinking about maintaining yet an other list of real↔proxy address pairs...