Bug 38263 – [Gtk] DNS prefetching trying to resolve empty host names, spamming syslog

• Status: RESOLVED
• Resolution: FIXED
• Component: Page Loading

[Michael Gratton]

WebKitGTK+ v1.2.0 (Ubuntu lucid libwebkit-1.0-2 1.2.0-1)

Webkit is causing programs that embed it to spam syslog with this sort of thing:

> Apr 29 00:17:01 localhost epiphany-browser: gethostby*.getanswer: asked for "", got "."
> Apr 29 00:18:07 localhost epiphany-browser: last message repeated 527 times
> Apr 29 00:19:08 localhost epiphany-browser: last message repeated 1178 times
> Apr 29 00:20:09 localhost epiphany-browser: last message repeated 1300 times
> Apr 29 00:21:18 localhost epiphany-browser: last message repeated 1341 times
> Apr 29 00:22:27 localhost epiphany-browser: last message repeated 715 times
> Apr 29 00:23:27 localhost epiphany-browser: last message repeated 1307 times
> Apr 29 00:24:27 localhost epiphany-browser: last message repeated 863 times
> Apr 29 00:25:27 localhost epiphany-browser: last message repeated 989 times
> Apr 29 00:26:27 localhost epiphany-browser: last message repeated 534 times

It looks like the DNS prefetching code is causing null/empty host names to be resolved, which explains the syslog entry. A typical stack trace is below. Note the call to g_resolver_lookup_by_name_async at the top with an empty hostname param.

I'm not sure where the best place to guard against this is, perhaps both GIO and Soup should be ignoring/erroring when invoked to resolve an empty host name, but libwebkitgtk probably shouldn't be attempting to prefetch links without a valid URI host part anyway.

#0  IA__g_resolver_lookup_by_name_async (resolver=0x20ef780, 
    hostname=0x39cace0 "", cancellable=0x0, callback=0x7fac17c2a2a0, 
    user_data=0x3516450) at /build/buildd/glib2.0-2.24.0/gio/gresolver.c:299
#1  0x00007fac17c2a18d in soup_address_resolve_async ()
   from /usr/lib/libsoup-2.4.so.1
#2  0x00007fac1904ee49 in WebCore::prefetchDNS (hostname=<value optimised out>)
    at ../WebCore/platform/network/soup/DNSSoup.cpp:44
#3  0x00007fac18d11670 in WebCore::Chrome::mouseDidMoveOverElement (
    this=0x7fabfd8e63c0, result=..., modifierFlags=27303232)
    at ../WebCore/page/Chrome.cpp:340
#4  0x00007fac18d2bd46 in WebCore::EventHandler::mouseMoved (
    this=<value optimised out>, event=...)
    at ../WebCore/page/EventHandler.cpp:1332
#5  0x00007fac19084055 in webkit_web_view_motion_event (
    widget=<value optimised out>, event=0x7fabe5c9a350)
    at ../WebKit/gtk/webkit/webkitwebview.cpp:654
#6  0x00007fac17fab0b8 in _gtk_marshal_BOOLEAN__BOXED (closure=0x1a09d40, 
    return_value=0x7fffad3488b0, n_param_values=<value optimised out>, 
    param_values=0x429a320, invocation_hint=<value optimised out>, 
    marshal_data=0x7fac19083ff0)
    at /build/buildd/gtk+2.0-2.20.0/gtk/gtkmarshalers.c:84
#7  0x00007fac16d925de in IA__g_closure_invoke (closure=0x1a09d40, 
    return_value=0x7fffad3488b0, n_param_values=2, param_values=0x429a320, 
---Type <return> to continue, or q <return> to quit---
    invocation_hint=0x7fffad348870)
    at /build/buildd/glib2.0-2.24.0/gobject/gclosure.c:767
#8  0x00007fac16da61dd in signal_emit_unlocked_R (node=0x1a09db0, 
    detail=<value optimised out>, instance=<value optimised out>, 
    emission_return=<value optimised out>, 
    instance_and_params=<value optimised out>)
    at /build/buildd/glib2.0-2.24.0/gobject/gsignal.c:3286
#9  0x00007fac16da78b9 in IA__g_signal_emit_valist (instance=0x7fabe5e2c810, 
    signal_id=<value optimised out>, detail=0, var_args=0x7fffad348a60)
    at /build/buildd/glib2.0-2.24.0/gobject/gsignal.c:2991
#10 0x00007fac16da8033 in IA__g_signal_emit (instance=0x20ef780, 
    signal_id=60599520, detail=0)
    at /build/buildd/glib2.0-2.24.0/gobject/gsignal.c:3038
#11 0x00007fac180c1e9f in gtk_widget_event_internal (widget=0x7fabe5e2c810, 
    event=0x7fabe5c9a350) at /build/buildd/gtk+2.0-2.20.0/gtk/gtkwidget.c:4951
#12 0x00007fac17fa3583 in IA__gtk_propagate_event (widget=0x7fabe5e2c810, 
    event=0x7fabe5c9a350) at /build/buildd/gtk+2.0-2.20.0/gtk/gtkmain.c:2447
#13 0x00007fac17fa465b in IA__gtk_main_do_event (event=0x7fabe5c9a350)
    at /build/buildd/gtk+2.0-2.20.0/gtk/gtkmain.c:1647
#14 0x00007fac179c580c in gdk_event_dispatch (source=<value optimised out>, 
    callback=<value optimised out>, user_data=<value optimised out>)
    at /build/buildd/gtk+2.0-2.20.0/gdk/x11/gdkevents-x11.c:2372
#15 0x00007fac166dd8c2 in g_main_dispatch (context=0x1a06310)
---Type <return> to continue, or q <return> to quit---
    at /build/buildd/glib2.0-2.24.0/glib/gmain.c:1960
#16 IA__g_main_context_dispatch (context=0x1a06310)
    at /build/buildd/glib2.0-2.24.0/glib/gmain.c:2513
#17 0x00007fac166e1748 in g_main_context_iterate (context=0x1a06310, 
    block=<value optimised out>, dispatch=<value optimised out>, 
    self=<value optimised out>)
    at /build/buildd/glib2.0-2.24.0/glib/gmain.c:2591
#18 0x00007fac166e1c55 in IA__g_main_loop_run (loop=0x1ab9fb0)
    at /build/buildd/glib2.0-2.24.0/glib/gmain.c:2799
#19 0x00007fac17fa4af7 in IA__gtk_main ()
    at /build/buildd/gtk+2.0-2.20.0/gtk/gtkmain.c:1219
#20 0x0000000000435423 in main (argc=1, argv=0x7fffad349fd8)
    at /build/buildd/epiphany-browser-2.30.2/src/ephy-main.c:741

[Alexey Proskuryakov]

We have the following in DNSCFNet.cpp (used in CFNetwork-based ports):

    if (hostname.isEmpty())
        return;

[Michael Gratton]

Created attachment 54769 [details]
Check hostname is non-empty before DNS prefetch

Per Alexey's suggestion, this adds an empty check on the hostname string before calling Soup to prefetch.

This patch fixes the problem for me.

[Sergio Villar Senin]

(In reply to comment #2)
> Created an attachment (id=54769) [details]
> Check hostname is non-empty before DNS prefetch
> 
> Per Alexey's suggestion, this adds an empty check on the hostname string before calling Soup to prefetch.
> 
> This patch fixes the problem for me.

Michael could you please include the proper changelog to the patch? There is some infor here http://webkit.org/coding/contributing.html. And do not forget to set the review flag to "?".

Adding Xan to the Cc BTW

[Gustavo Noronha (kov)]

Is this now obsolete? After 56128 the way this is done is completely different for the GTK+ port, and I was unable to identify at a glance if we would still be able to suffer from the same problem. Can the URL passed to prepareForURL lack a host?

[Michael Gratton]

I'm not getting the syslog spam any more with webkit 1.4, soup 2.34 and glib  2.28, but I guess that's not to say the problem isn't still there.

Gustavo, bug #56128 doesn't seem relevant?

[Gustavo Noronha (kov)]

(In reply to comment #5)
> Gustavo, bug #56128 doesn't seem relevant?

I meant revision 56128: http://trac.webkit.org/changeset/56128

[Michael Gratton]

(In reply to comment #6)
> 
> I meant revision 56128: http://trac.webkit.org/changeset/56128

Oh, of course, thanks.

Well, that revision uses soup_session_prepare_for_uri() for the DNS prefetching, and that function (in libsoup git master anyway) does a null check on the host, so this can probably be resolved as invalid or wontfix now.

[Michael Gratton]

One note, possibly for another bug: Since HTMLAnchorElement::parseMappedAttribute calls ResourceHandle::prepareForURL, whenever an anchor element's href attribute is changed (which I assume also happens when the element is first parsed), loading a page will cause every anchor's href to be prefetched.

This doesn't strike me as being very desirable, but I guess that is a WebKit issue in general.

[Gustavo Noronha (kov)]

Well, fixed, just by a different patch, then =)