Bug 284246 – AX: Crash in AtspiObject->textAttributesWithUTF8Offset

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: Accessibility

[Mike Gorse]

Steps to reproduce:
1. Enable screen reader. I'm using Orca 47.2; I'm guessing that anything >= 47 will work.
2. Start evolution.
3. Set up a gmail/google account. Start the oauth flow.
4. Press tab a few times to focus the next button.

#3  0x00007f48f662891a in __GI_abort () at abort.c:79
79            raise (SIGABRT);
#4  0x00007f48fdf77454 in WTF::CrashOnOverflow::crash () at /home/mgorse/src/WebKit/t/WTF/Headers/wtf/CheckedArithmetic.h:109
109             CRASH();
#5  0x00007f48fdf7744b in WTF::CrashOnOverflow::overflowed () at /home/mgorse/src/WebKit/t/WTF/Headers/wtf/CheckedArithmetic.h:102
102             crash();
#6  0x00007f490244f82d in WTF::Vector<unsigned int, 128ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>::at (this=0x7ffd82b2a0d0, i=4) at /home/mgorse/src/WebKit/t/WTF/Headers/wtf/Vector.h:847
847                 OverflowHandler::overflowed();
#7  0x00007f490244ed23 in WTF::Vector<unsigned int, 128ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>::operator[] (this=0x7ffd82b2a0d0, i=4) at /home/mgorse/src/WebKit/t/WTF/Headers/wtf/Vector.h:852
852         const T& operator[](size_t i) const { return at(i);
}
#8  0x00007f4902449323 in WebCore::UTF16OffsetToUTF8 (mapping=WTF::Vector of length 2, capacity 128 = {...}, offset=4) at /home/mgorse/src/WebKit/Source/WebCore/accessibility/atspi/AccessibilityObjectTextAtspi.cp
p:256
256         return mapping.isEmpty() ? offset : mapping[offset];
#9  0x00007f490244e0e6 in WebCore::AccessibilityObjectAtspi::textAttributesWithUTF8Offset (this=0x7f48e9d35080, offset=std::optional = {...}, includeDefault=true)
    at /home/mgorse/src/WebKit/Source/WebCore/accessibility/atspi/AccessibilityObjectTextAtspi.cpp:935
935             attributes.startOffset = UTF16OffsetToUTF8(mapping, attributes.startOffset);
(gdb)
#10 0x00007f490244820a in operator() (__closure=0x0, methodName=0x7f48d4007470 "GetAttributeRun", parameters=0x7f48d4008310, invocation=0x7f48d40050c0, userData=0x7f48e9d35080)
    at /home/mgorse/src/WebKit/Source/WebCore/accessibility/atspi/AccessibilityObjectTextAtspi.cpp:139
139                 auto attributes = atspiObject->textAttributesWithUTF8Offset(offset, includeDefaults);

[Radar WebKit Bug Importer]

<rdar://problem/141119347>

[Mike Gorse]

The object triggering this contains one U+fffc character. The code in AccessibilityObjectAtspi::TextAttributes looks like it can recurse into an object's children, while the caller has a UTF16 -> UTF8 mapping for the text in the object itself, so just the U+fffc character.

[Mike Gorse]

AccessibilityObjectAtspi::TextAttributes() has this:
    auto firstValidPosition = firstPositionInOrBeforeNode(m_coreObject->node()->firstDescendant());
...
    auto startPosition = firstPositionInOrBeforeNode(startRenderer->node());
    for (RenderObject* r = childRenderer->previousInPreOrder(); r && startPosition > firstValidPosition; r = r->previousInPreOrder()) {
...
    auto startOffset = adjustOutputOffset(m_coreObject->indexForVisiblePosition(startPosition), m_hasListMarkerAtStart);

startOffset is set to 4, and the code in the loop never executes because
startPosition == firstValidPosition. I think that the accessible is
encapsulating a button labeled "next", which might be where the 4 is coming
from, but the accessible's text contains the object replacement character,
rather than "next".

[Mike Gorse]

Okay, my guess in my last comment was wrong. I tried changing the language on the page to Spanish, which changed the label on the button to "Siguiente," and the returned attribute offset is still 4. The "create account" button on the same page also triggers the crash for me, and 2 is returned there for the start offset.

[Mike Gorse]

Marking this as a dup; making the change described in bug 270354 would likely fix this.

*** This bug has been marked as a duplicate of bug 270354 ***