[Bug 1295229] Re: With 'hosts: mdns4' in nsswitch.conf, getaddrinfo() returns -5 (EAI_NODATA) when network interface is down

[Trent Lloyd]

Did a quick test with the originally attached test file, this only
happens if 'mdns4' is last on the nsswitch.conf line.  I don't think
this is the default we ship anymore, we currently ship:

hosts:          files mdns4_minimal [NOTFOUND=return] dns

TJ: Do you have the exact nsswitch.conf line the user was using?


With regards to the multi second timeouts.. this should only happen if the user is looking up a .local hostname or reverse DNS specifically for 169.254.x.x.. I'd also wonder if they had a interface with a 169.254 link-local address assigned.  Do you also happen to have the output of "ip addr" and "ip -6 addr"

Alternative I am lathiat on IRC, maybe you can put me in contact with
the user?

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Title:
  With 'hosts: mdns4' in nsswitch.conf, getaddrinfo() returns -5
  (EAI_NODATA) when network interface is down

Status in nss-mdns package in Ubuntu:
  Confirmed

Bug description:
  When  the "hosts:" line in nsswitch.conf includes `mdns4` or
  `mdns4_minimal` last and the network interface is taken down,
  getaddrinfo() returns -5 (EAI_NODATA — "No address associated with
  hostname") instead of something more appropriate such as -4 (EAI_FAIL
  — "Non-recoverable failure in name resolution").

  $ dpkg -l libc6
  [...]
  ii libc6:amd64 2.17-93ubuntu4 amd64

  $ grep hosts /etc/nsswitch.conf
  hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4

  $ sudo su
  # ifconfig eth0 down
  # ./a.out
  Making resolv.conf empty
  Results of looking up www.google.com: status = -5, errno = 110
  Results of looking up a bogus name: status = -5, errno = 110
  Writing correct nameserver option to resolv.conf
  Results of looking up www.google.com: status = -5, errno = 110
  Results of looking up a bogus name: status = -5, errno = 110
  Writing incorrect nameserver option to resolv.conf
  Results of looking up www.google.com: status = -5, errno = 110
  Results of looking up a bogus name: status = -5, errno = 110

  # cat x.c
  #include <sys/types.h>
  #include <sys/socket.h>
  #include <netdb.h>
  #include <errno.h>
  #include <stdio.h>

  struct addrinfo *res;

  void check_google()
  {
      int status;
      status = getaddrinfo("www.google.com", NULL, NULL, &res);
      printf("Results of looking up www.google.com: status = %d, errno = %d\n", status, errno);
      status = getaddrinfo("sjfkdsjfswfloo0f02938sjf28398sd.com", NULL, NULL, &res);
      printf("Results of looking up a bogus name: status = %d, errno = %d\n", status, errno);
  }

  int main()
  {
      FILE *fp;

      printf("Making resolv.conf empty\n");
      fp = fopen("/etc/resolv.conf", "w+"); fclose(fp);
      sleep(1);
      check_google();

      printf("Writing nameserver option to resolv.conf\n");
      fp = fopen("/etc/resolv.conf", "w+"); fprintf(fp, "nameserver 193.67.79.39\n"); fclose(fp);
      sleep(1);
      check_google();

      printf("Writing incorrect nameserver option to resolv.conf\n");
      fp = fopen("/etc/resolv.conf", "w+"); fprintf(fp, "nameserver 192.168.5.4\n"); fclose(fp);
      sleep(1);
      check_google();
  }

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