Guard surrounding_text against out-of-bounds cursor/anchor offsets#133
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Guard surrounding_text against out-of-bounds cursor/anchor offsets#133thereisnotime wants to merge 1 commit into
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The compositor's cursor and anchor byte offsets are passed straight into QString::fromUtf8 as lengths with no validation. A bogus offset larger than the text (KWin on Plasma 6 sends values like 6881396) makes fromUtf8 read past the end of the buffer and segfault, which is the frequent maliit-keyboard crash in maliit/keyboard#262. Clamp cursor and anchor to the text length before use.
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The Wayland input-method
surrounding_texthandler inconnection/waylandinputmethodconnection.cppuses the compositor-suppliedcursorandanchorbyte offsets directly asQString::fromUtf8lengths, with no bounds check:When a compositor sends an offset larger than the text (KWin on Plasma 6 sends values like 6881396),
fromUtf8reads past the end of the buffer and the process segfaults in_mm_loadu_si128. This is the frequent maliit-keyboard crash reported in maliit/keyboard#262 (and earlier in #86), and it makes the keyboard drop out constantly on Fedora 43 + Plasma 6 Wayland.This clamps
cursorandanchorto the actual UTF-8 length before they are used as offsets/lengths, which also keeps thebegin/endselection slice in bounds. It is purely defensive: valid offsets are unchanged.Refs maliit/keyboard#262.