(release/25.0) xkb: Fix off-by-one and NULL dereferences in _CheckSetOverlay()#2796
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Off-by-one in rowUnder validation: the bounds check uses '>' instead of '>=' when comparing rWire->rowUnder against section->num_rows. Since num_rows is a count and valid indices are 0 to num_rows-1, rowUnder == num_rows passes the check but is one past the valid range. XkbAddGeomOverlayRow() uses this as an array index, causing an out-of-bounds read on section->rows[]. And throw in two alloc checks while we're at it. Assisted-by: Claude:claude-claude-opus-4-6 Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2208>
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Off-by-one in rowUnder validation: the bounds check uses '>' instead
of '>=' when comparing rWire->rowUnder against section->num_rows.
Since num_rows is a count and valid indices are 0 to num_rows-1,
rowUnder == num_rows passes the check but is one past the valid range.
XkbAddGeomOverlayRow() uses this as an array index, causing an
out-of-bounds read on section->rows[].
And throw in two alloc checks while we're at it.
Assisted-by: Claude:claude-claude-opus-4-6
Part-of: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2208