Summary of why the last resort fallback font is chosen:

1. Skipping "RenderSandboxHostLinux::GetInstance()->Init()", in addition to crashing Chrome, means that the GetSandboxFD() is never initialized, despite being required by the font code if sandboxEnabled return true [1]. 

2. when zygote is disabled FontConfigIPC is never set to the SkFontConfigInterface [2] 

The first issue prevents font selection from working (IPC breaks so it uses an empty font description), and the second issue prevents font loading from working (It tries to load based off fontconfigInterfaceId instead of filename)

[1]
https://cs.chromium.org/chromium/src/content/child/child_process_sandbox_support_impl_linux.cc?rcl=86767028eea938a79b9b814ca3fe6f4396e38387&l=87
[2]
https://cs.chromium.org/chromium/src/content/zygote/zygote_main_linux.cc?rcl=dfc326b3c2dc9801898bba2d0f1cd2de52f83c9d&l=374

There is a TSan data race report if zygote is disabled, "RenderSandboxHostLinux::GetInstance()->Init()" is run, and the fontconfig sandbox code is enabled (RendererBlinkPlatformImpl::sandboxEnabled() returns true).

See attached.

Deleted: tsan_report.txt 4.0 KB

tsan_report.txt 4.0 KB View Download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9dc1413a9f8a803109530c02aeb4429a8856e525

commit 9dc1413a9f8a803109530c02aeb4429a8856e525
Author: zoeclifford <zoeclifford@chromium.org>
Date: Thu Apr 20 22:36:30 2017

Initialize RenderSandboxHostLinux in --no-zygote mode to not crash.

http://crrev.com/2384163002 skipped initializing RenderSandboxHostLinux
If the sandbox and zygote are both disabled. But the RendererSocket is
used even in this case by the Linux ChildProcessLauncherHelper, so it
lead to a crash.

Instead initialize the RenderSandboxHostLinux unconditionally. This
appears to be what some code expects in multi-process code.

Tested:
cr run chrome --no-zygote --no-sandbox http://www.google.com

BUG= 712779 

Review-Url: https://codereview.chromium.org/2827783003
Cr-Commit-Position: refs/heads/master@{#466168}

[modify] https://crrev.com/9dc1413a9f8a803109530c02aeb4429a8856e525/content/browser/browser_main_loop.cc
[modify] https://crrev.com/9dc1413a9f8a803109530c02aeb4429a8856e525/content/zygote/zygote_browsertest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/525974cdba654d1611d169a34397304334797175

commit 525974cdba654d1611d169a34397304334797175
Author: zoeclifford <zoeclifford@chromium.org>
Date: Wed May 17 20:31:06 2017

Initialize FontConfigIPC when zygote is disabled so font fallback works.

Normally FontConfigIPC is set from zygote_main_linux, but this can't
happen if zygote is disabled, either from the --no-zygote flag or the
--renderer-cmd-prefix flag.

This is a problem because the renderer's font code uses the linux
sandbox IPC logic even if --no-sandbox is set. This code mostly works
but fallback font loading fails because when FontConfigIPC isn't set,
SkFontConfigInterfaceDirect is used instead, and it doesn't know how
to deal with fontconfiginterfaceids. This causes the last resort
fallback font to always be chosen, even when a more appropriate font
is available.

To fix this, simply initialize FontConfigIPC even when zygote is
disabled. This lets the existing code work, and allows fallback fonts
to be loaded.

Manually tested with the test-case in  http://crbug.com/712779 

BUG= 712779 

Review-Url: https://codereview.chromium.org/2833973003
Cr-Commit-Position: refs/heads/master@{#472553}

[add] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/browser/linux_ipc_browsertest.cc
[modify] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/browser/renderer_host/sandbox_ipc_linux.cc
[modify] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/browser/renderer_host/sandbox_ipc_linux.h
[modify] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/renderer/renderer_main.cc
[modify] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/test/BUILD.gn
[add] https://crrev.com/525974cdba654d1611d169a34397304334797175/content/test/data/font/font_fallback.html