WebContent process crashed when resolving UiMonospace

[bourdeau]

Summary

Ladybird crashes when trying to resolve the UiMonospace font. The WebContent process fails with:

VERIFICATION FAILED: m_default_font at /build/source/Libraries/LibWebView/Plugins/FontPlugin.cpp:47

My system's default monospace font (according to fc-match monospace) is JetBrainsMono Nerd Font. The crash occurs at:

auto default_fixed_width_font_name = generic_font_name(Web::Platform::GenericFont::UiMonospace);

It seems that generic_font_name(UiMonospace) may be returning an invalid or empty font name, causing the crash.

Operating system

Linux

Steps to reproduce

1.Install and run Ladybird on NixOS (https://github.com/NixOS/nixpkgs/blob/nixos-24.11/pkgs/applications/networking/browsers/ladybird/default.nix#L155)
2. Ensure that the system’s default monospace font is JetBrainsMono Nerd Font (check with fc-match monospace).
3. Open Ladybird and navigate to any page (or just about:newtab).
4. Observe that the WebContent process crashes.

Expected behavior

No crash

Actual behavior

Crashes

URL for a reduced test case

N/A

HTML/SVG/etc. source for a reduced test case

N/A

Log output and (if possible) backtrace

3249.845 Ladybird(18272): WebContent process crashed! Last page loaded: about:newtab
3249.845 Ladybird(18272): Consider raising an issue at https://github.com/LadybirdBrowser/ladybird/issues/new/choose
3249.845 Ladybird(18272): WebContent has crashed 5 times in quick succession! Not restarting...
VERIFICATION FAILED: m_default_font at /build/source/Libraries/LibWebView/Plugins/FontPlugin.cpp:47
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/../lib/liblagom-ak.so.0(ak_verification_failed+0x83) [0x7f011d3a15f3]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/../lib/liblagom-webview.so.0 WebView::FontPlugin::FontPlugin(bool, Gfx::SystemFontProvider*) 0x3f4) [0x7f011fafd9a4]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent() [0x42ae9f]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent(main+0xf2) [0x429632]
/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6(+0x2a27e) [0x7f011ce3127e]
/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6(__libc_start_main+0x89) [0x7f011ce31339]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent() [0x429765]
3281.600 Ladybird(18272): WebContent process crashed! Last page loaded: about:newtab
3281.600 Ladybird(18272): Consider raising an issue at https://github.com/LadybirdBrowser/ladybird/issues/new/choose
VERIFICATION FAILED: m_default_font at /build/source/Libraries/LibWebView/Plugins/FontPlugin.cpp:47
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/../lib/liblagom-ak.so.0(ak_verification_failed+0x83) [0x7f54b21a15f3]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/../lib/liblagom-webview.so.0 WebView::FontPlugin::FontPlugin(bool, Gfx::SystemFontProvider*) 0x3f4) [0x7f54b48fd9a4]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent() [0x42ae9f]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent(main+0xf2) [0x429632]
/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6(+0x2a27e) [0x7f54b1c3127e]
/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6(__libc_start_main+0x89) [0x7f54b1c31339]
/nix/store/2dg8q88zp8dd8an2722q0d21b54f6c4z-ladybird-0-unstable-2024-11-21/libexec/WebContent() [0x429765]
3281.708 Ladybird(18272): WebContent process crashed! Last page loaded: about:newtab

Screenshots or screen recordings

No response

Build flags or config settings

No response

Contribute a patch?

• I’ll contribute a patch for this myself.

[AtkinsSJ]

That nix package installs a version from November last year. That VERIFY that triggers no longer appears in the code, see 0b8b690#diff-b4193d5184c5c7b5cc1e3c15e919e0798bdd4e648644a485fc3435e6eb50a4f5L47 - can you try building from the master branch and seeing if you still get issues?