djbdns: fix crash due to data ulimit

This fixes: https://github.com/NixOS/nixpkgs/issues/119066.

When `djbdns` is repeatedly queried it will crash with:

```
mmap: tinydns (842): VmData 331776 exceed data ulimit 300000. Update limits or use boot option ignore_rlimit_data.
```

So we increase the softlimit from 300000 to 4500000 as suggested in
the issue.

The `tinydns` NixOS test has been extended with testing for the faulty
behaviour.

nixos/tests/tinydns.nix

@@ -21,6 +21,20 @@ import ./make-test-python.nix ({ lib, ...} : {
   testScript = ''
     nameserver.start()
     nameserver.wait_for_unit("tinydns.service")
-    nameserver.succeed("host bla.foo.bar 192.168.1.1 | grep '1\.2\.3\.4'")
+
+    # We query tinydns a few times to trigger the bug:
+    #
+    #   nameserver # [    6.105872] mmap: tinydns (842): VmData 331776 exceed data ulimit 300000. Update limits or use boot option ignore_rlimit_data.
+    #
+    # which was reported in https://github.com/NixOS/nixpkgs/issues/119066.
+    # Without the patch <nixpkgs/pkgs/tools/networking/djbdns/softlimit.patch>
+    # it fails on the 10th iteration.
+    nameserver.succeed(
+        """
+          for i in {1..15}; do
+            host bla.foo.bar 192.168.1.1 | grep '1\.2\.3\.4'
+          done
+        """
+    )
   '';
 })

pkgs/tools/networking/djbdns/default.nix

@@ -19,7 +19,14 @@ stdenv.mkDerivation {
     sha256 = "0j3baf92vkczr5fxww7rp1b7gmczxmmgrqc8w2dy7kgk09m85k9w";
   };
 
-  patches = [ ./hier.patch ./fix-nix-usernamespace-build.patch ];
+  patches = [
+    ./hier.patch
+    ./fix-nix-usernamespace-build.patch
+
+    # To fix https://github.com/NixOS/nixpkgs/issues/119066.
+    # Note that the NixOS test <nixpkgs/nixos/tests/tinydns.nix> tests for this.
+    ./softlimit.patch
+  ];
 
   postPatch = ''
     echo gcc -O2 -include ${glibc.dev}/include/errno.h > conf-cc

pkgs/tools/networking/djbdns/softlimit.patch

@@ -0,0 +1,12 @@
+diff -Naur a/tinydns-conf.c b/tinydns-conf.c
+--- a/tinydns-conf.c	2001-02-11 21:11:45.000000000 +0000
++++ b/tinydns-conf.c	2021-11-08 17:23:06.181385437 +0000
+@@ -46,7 +46,7 @@
+
+   start("run");
+   outs("#!/bin/sh\nexec 2>&1\nexec envuidgid "); outs(user);
+-  outs(" envdir ./env softlimit -d300000 ");
++  outs(" envdir ./env softlimit -d4500000 ");
+   outs(auto_home); outs("/bin/tinydns\n");
+   finish();
+   perm(0755);