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LibWeb: Clamp layout content sizes to a max value instead of crashing

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We've historically asserted that no "saturated" size values end up as
final metrics for boxes in layout. This always had a chance of producing
false positives, since you can trivially create extremely large boxes
with CSS.

The reason we had those assertions was to catch bugs in our own engine
code where we'd incorrectly end up with non-finite values in layout
algorithms. At this point, we've found and fixed all known bugs of that
nature, and what remains are a bunch of false positives on pages that
create very large scrollable areas, iframes etc.

So, let's change it! We now clamp content width and height of boxes to
17895700 pixels, apparently the same cap as Firefox uses.

There's also the issue of calc() being able to produce non-finite
values. Note that we don't clamp the result of calc() directly, but
instead just clamp values when assigning them to content sizes.

Fixes #645.
Fixes #1236.
Fixes #1249.
Fixes #1908.
Fixes #3057.
This commit is contained in:
Andreas Kling 2025-02-05 14:13:33 +01:00 • committed by Andreas Kling
commit 4f855286d7
Notes: github-actions[bot] 2025-02-05 17:46:43 +00:00
7 changed files with 40 additions and 50 deletions
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31
Libraries/LibWeb/Layout/LayoutState.cpp
View file

@ -535,13 +535,14 @@ void LayoutState::UsedValues::set_node(NodeWithStyle& node, UsedValues const* co
|| node.parent()->display().is_flow_inside())) {
if (containing_block_has_definite_size) {
CSSPixels available_width = containing_block_used_values->content_width();
resolved_definite_size = available_width
resolved_definite_size = clamp_to_max_dimension_value(
available_width
- margin_left
- margin_right
- padding_left
- padding_right
- border_left
- border_right;
- border_right);
return true;
}
return false;
@ -559,19 +560,19 @@ void LayoutState::UsedValues::set_node(NodeWithStyle& node, UsedValues const* co
auto containing_block_size_as_length = width ? containing_block_used_values->content_width() : containing_block_used_values->content_height();
context.percentage_basis = CSS::Length::make_px(containing_block_size_as_length);
}
resolved_definite_size = adjust_for_box_sizing(size.calculated().resolve_length(context)->to_px(node), size, width);
resolved_definite_size = clamp_to_max_dimension_value(adjust_for_box_sizing(size.calculated().resolve_length(context)->to_px(node), size, width));
return true;
}
if (size.is_length()) {
VERIFY(!size.is_auto()); // This should have been covered by the Size::is_auto() branch above.
resolved_definite_size = adjust_for_box_sizing(size.length().to_px(node), size, width);
resolved_definite_size = clamp_to_max_dimension_value(adjust_for_box_sizing(size.length().to_px(node), size, width));
return true;
}
if (size.is_percentage()) {
if (containing_block_has_definite_size) {
auto containing_block_size = width ? containing_block_used_values->content_width() : containing_block_used_values->content_height();
resolved_definite_size = adjust_for_box_sizing(containing_block_size.scaled(size.percentage().as_fraction()), size, width);
resolved_definite_size = clamp_to_max_dimension_value(adjust_for_box_sizing(containing_block_size.scaled(size.percentage().as_fraction()), size, width));
return true;
}
return false;
@ -600,10 +601,10 @@ void LayoutState::UsedValues::set_node(NodeWithStyle& node, UsedValues const* co
if (m_has_definite_width && m_has_definite_height) {
// Both width and height are definite.
} else if (m_has_definite_width) {
m_content_height = m_content_width / *aspect_ratio;
m_content_height = clamp_to_max_dimension_value(m_content_width / *aspect_ratio);
m_has_definite_height = true;
} else if (m_has_definite_height) {
m_content_width = m_content_height * *aspect_ratio;
m_content_width = clamp_to_max_dimension_value(m_content_height * *aspect_ratio);
m_has_definite_width = true;
}
}
@ -611,28 +612,27 @@ void LayoutState::UsedValues::set_node(NodeWithStyle& node, UsedValues const* co
if (m_has_definite_width) {
if (has_definite_min_width)
m_content_width = max(min_width, m_content_width);
m_content_width = clamp_to_max_dimension_value(max(min_width, m_content_width));
if (has_definite_max_width)
m_content_width = min(max_width, m_content_width);
m_content_width = clamp_to_max_dimension_value(min(max_width, m_content_width));
}
if (m_has_definite_height) {
if (has_definite_min_height)
m_content_height = max(min_height, m_content_height);
m_content_height = clamp_to_max_dimension_value(max(min_height, m_content_height));
if (has_definite_max_height)
m_content_height = min(max_height, m_content_height);
m_content_height = clamp_to_max_dimension_value(min(max_height, m_content_height));
}
}
void LayoutState::UsedValues::set_content_width(CSSPixels width)
{
VERIFY(!width.might_be_saturated());
if (width < 0) {
// Negative widths are not allowed in CSS. We have a bug somewhere! Clamp to 0 to avoid doing too much damage.
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Layout calculated a negative width for {}: {}", m_node->debug_description(), width);
width = 0;
}
m_content_width = width;
m_content_width = clamp_to_max_dimension_value(width);
// FIXME: We should not do this! Definiteness of widths should be determined early,
// and not changed later (except for some special cases in flex layout..)
m_has_definite_width = true;
@ -640,18 +640,17 @@ void LayoutState::UsedValues::set_content_width(CSSPixels width)
void LayoutState::UsedValues::set_content_height(CSSPixels height)
{
VERIFY(!height.might_be_saturated());
if (height < 0) {
// Negative heights are not allowed in CSS. We have a bug somewhere! Clamp to 0 to avoid doing too much damage.
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Layout calculated a negative height for {}: {}", m_node->debug_description(), height);
height = 0;
}
m_content_height = height;
m_content_height = clamp_to_max_dimension_value(height);
}
void LayoutState::UsedValues::set_temporary_content_width(CSSPixels width)
{
m_content_width = width;
m_content_width = clamp_to_max_dimension_value(width);
}
void LayoutState::UsedValues::set_temporary_content_height(CSSPixels height)