[OpenSIPS-Devel] [OpenSIPS/opensips] 17558c: mk_proxy(): Improve robustness

[Liviu Chircu]

  Branch: refs/heads/master
  Home:   https://github.com/OpenSIPS/opensips
  Commit: 17558c5bdac952899aee705a654725c786c6348f
      https://github.com/OpenSIPS/opensips/commit/17558c5bdac952899aee705a654725c786c6348f
  Author: Liviu Chircu <liviu at opensips.org>
  Date:   2019-08-17 (Sat, 17 Aug 2019)

  Changed paths:
    M proxy.c

  Log Message:
  -----------
  mk_proxy(): Improve robustness

A lot of code which calls mk_proxy() for DNS resolution assumes that
the "proxy->host->h_addr_list" array contains at least one value, e.g.:

modules/drouting/routing.c +611:
    hostent2ip_addr(&pgw->ips[0], &proxy->host, proxy->addr_idx);

modules/dispatcher/dispatch.c +281:
    hostent2ip_addr( &dp->ips[0], &proxy->host, proxy->addr_idx);

This would cause a segfault immediately if h_addr_list contains 0
results (i.e. first value is a NULL pointer).  As the overall intention
is to resolve the hostname into at least 1 IP address, this patch
changes mk_proxy() to return NULL on a successful query with 0 results.

Credits to Jonathan Hulme for the report