bug#43071: Enable WebKit sandboxing

bug#43071: Enable WebKit sandboxing

[Paul Eggert]

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Qiantan Hong suggested that Emacs should enable sandboxing in WebKit, for all 
the usual security reasons. (Thanks, Qiantan!)

Attached is a proposed patch to implement that suggestion; it's a bit fancier 
than what Qiantan originally proposed in 
<https://lists.gnu.org/r/emacs-devel/2020-08/msg00896.html> because it checks 
that WebKit 2.26 or later is in use, and it avoids a duplicate call to 
webkit_web_context_get_default. I'm cc'ing this to Qiantan and to other recent 
committers to xwidget.c, to get their opinions.

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From 1ca9d47923813e536753c18aa15194f15f39ab3d Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 27 Aug 2020 06:00:52 -0700
Subject: [PATCH] Use WebKit sandboxing

* src/xwidget.c (Fmake_xwidget): Enable sandboxing if WebKit 2.26
or later.  Do this early, as required for sandboxing.
Co-authored-by: Qiantan Hong <qhong@mit.edu>
Copyright-paperwork-exempt: yes
---
 src/xwidget.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/xwidget.c b/src/xwidget.c
index 154b3e9c82..851f96952c 100644
--- a/src/xwidget.c
+++ b/src/xwidget.c
@@ -114,6 +114,13 @@ DEFUN ("make-xwidget",
   if (EQ (xw->type, Qwebkit))
     {
       block_input ();
+      WebKitWebContext *webkit_context = webkit_web_context_get_default ();
+
+# if WEBKIT_CHECK_VERSION (2, 26, 0)
+      if (!webkit_web_context_get_sandbox_enabled (webkit_context))
+	webkit_web_context_set_sandbox_enabled (webkit_context, TRUE);
+# endif
+
       xw->widgetwindow_osr = gtk_offscreen_window_new ();
       gtk_window_resize (GTK_WINDOW (xw->widgetwindow_osr), xw->width,
                          xw->height);
@@ -152,7 +159,7 @@ DEFUN ("make-xwidget",
                             "load-changed",
                             G_CALLBACK (webkit_view_load_changed_cb), xw);
 
-          g_signal_connect (G_OBJECT (webkit_web_context_get_default ()),
+          g_signal_connect (G_OBJECT (webkit_context),
                             "download-started",
                             G_CALLBACK (webkit_download_cb), xw);
 
-- 
2.25.4

bug#43071: Enable WebKit sandboxing

[Stefan Kangas]

Paul Eggert <eggert@cs.ucla.edu> writes:

> Qiantan Hong suggested that Emacs should enable sandboxing in WebKit, for all
> the usual security reasons. (Thanks, Qiantan!)
>
> Attached is a proposed patch to implement that suggestion; it's a bit fancier
> than what Qiantan originally proposed in
> <https://lists.gnu.org/r/emacs-devel/2020-08/msg00896.html> because it checks
> that WebKit 2.26 or later is in use, and it avoids a duplicate call to
> webkit_web_context_get_default. I'm cc'ing this to Qiantan and to other recent
> committers to xwidget.c, to get their opinions.

Thanks Qiantan Hong and Paul Eggert.

Is this important enough to warrant backporting to emacs-26?

bug#43071: Enable WebKit sandboxing

[Jimmy Aguilar Mena]

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It looks fine for me.

Maybe it should be added as a security patch for the 27.* branch.

On Thu, 27 Aug 2020 at 15:14, Paul Eggert <eggert@cs.ucla.edu> wrote:

> Qiantan Hong suggested that Emacs should enable sandboxing in WebKit, for
> all
> the usual security reasons. (Thanks, Qiantan!)
>
> Attached is a proposed patch to implement that suggestion; it's a bit
> fancier
> than what Qiantan originally proposed in
> <https://lists.gnu.org/r/emacs-devel/2020-08/msg00896.html> because it
> checks
> that WebKit 2.26 or later is in use, and it avoids a duplicate call to
> webkit_web_context_get_default. I'm cc'ing this to Qiantan and to other
> recent
> committers to xwidget.c, to get their opinions.
>

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bug#43071: Enable WebKit sandboxing

[Paul Eggert]

On 8/27/20 6:41 AM, Stefan Kangas wrote:
> Is this important enough to warrant backporting to emacs-26?

I would think so, yes. It's security-relevant, and its effects should be limited 
to GNU/Linux distros that configure Emacs using --with-xwidgets.

bug#43071: Enable WebKit sandboxing

[Qiantan Hong]

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Just a follow up, what’s the status on this patch?

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bug#43071: Enable WebKit sandboxing

[Paul Eggert]

No further comment, so I installed the WebKit sandboxing patch into the emacs-27 
branch on Savannah 
<https://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-27&id=71661b287297f328c2c5ad67e180a760f80850cb>. 
After the next merge from emacs-27 to master, this patch should appear in the 
master branch. I am closing Bug#43071.

While testing the fix, I ran into a problem with xwidgets and filed Bug#44204 
"Emacs --with-xwidgets complains under Ubuntu 20.04" which you can see here:

https://bugs.gnu.org/44204

Has anyone had luck running Emacs --with-xwidgets under Ubuntu 20.04 or later? 
I'll cc. this to 44204@debbugs.gnu.org to try to move that part of the 
discussion there.