Bug#968888: vsftpd silently botches pasv_address setting if listen_ipv6 has been left to its default value

[Alain Knaff]

Package: vsftpd
Version: 3.0.3-12

Hi,

The pasv_address setting in vsftpd does not work if listen_ipv6 is set, 
with no clear error message anywhere in the log about what is going on.

This setting is used for ftp servers behind a reverse NAT.

If used while listen_ipv6=YES (as in default sample configuration 
shipped), the address specified in pasv_address is ignored, but instead 
0.0.0.0 is used, even if the client did indeed connect via IPV4.

Analysis:

at the top of function handle_pasv(), vsftpd does the following:

  int is_ipv6 = vsf_sysutil_sockaddr_is_ipv6(p_sess->p_local_addr);


... and then later:

  if (!is_ipv6)
  {
    str_append_text(&s_pasv_res_str, vsf_sysutil_inet_ntop(s_p_sockaddr));
  }
  else
  {
    const void* p_v4addr = vsf_sysutil_sockaddr_ipv6_v4(s_p_sockaddr);
    if (p_v4addr)
    {
      str_append_text(&s_pasv_res_str, vsf_sysutil_inet_ntoa(s_p_sockaddr));
    }
    else
    {
      str_append_text(&s_pasv_res_str, "0,0,0,0");
    }
  }

The first "if" goes into the second branch (address considered as IPv6).
The second "if" tests whether the s_p_sockaddr is indeed IPv6 (which it 
is not), and if not falls back to 0,0,0,0


Shouldn't this be a single test?

    const void* p_v4addr = vsf_sysutil_sockaddr_ipv6_v4(s_p_sockaddr);
    if (p_v4addr)
    {
      str_append_text(&s_pasv_res_str, vsf_sysutil_inet_ntoa(s_p_sockaddr));
    }
    else
    {
      vsf_sysutil_inet_ntop(s_p_sockaddr);
    }

... or something similar?

Or if for some reason this is not doable, at least loudly warn in the 
log file if this condition occurs (pasv_address used along with 
listen_ipv6=YES)

Thanks,

Alain