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lib/raster3d: fix int overflow in Rast3d_copy_values byte offset - #7970
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… offset. eltLength, offsSrc and offsDst are all int, so the byte offset is multiplied in 32-bit arithmetic. G_incr_void_ptr() (lib/gis/alloc.c:182) already takes a size_t, but the product has overflowed before it gets there. In our crash, the element offset was 681 M, which fits in an int. Multiplied by 4 bytes for FCELL it becomes 2.7 G, which overflows, goes negative, and memcpy writes before the buffer. The minimal fix: widen the multiplication to size_t: 67 src = G_incr_void_ptr(src, (size_t)eltLength * offsSrc); 68 dst = G_incr_void_ptr(dst, (size_t)eltLength * offsDst); That fixes our case: blocks of up to 2³¹ − 1 cells, which is 8 GiB of FCELL. Line 70 already casts the memcpy length the same way ((size_t)nElts * eltLength), so the fix makes lines 67–68 consistent with the line just below them. A complete fix for blocks over 2³¹ cells would also need two more changes. Both alter the public API, so they suit a separate PR: - lib/raster3d/getblock.c:66–67 computes the destination offset (z + dz) * nx * ny + (y + dy) * nx + (x + dx) in int. - Rast3d_copy_values() takes its offsets as int (the prototype is at include/grass/defs/raster3d.h:173). Both would have to become size_t.
nilason
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nilason
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Sep 29, 2026
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… offset.
eltLength, offsSrc and offsDst are all int, so the byte offset is multiplied in 32-bit arithmetic. G_incr_void_ptr() (lib/gis/alloc.c:182) already takes a size_t, but the product has overflowed before it gets there. In our crash, the element offset was 681 M, which fits in an int. Multiplied by 4 bytes for FCELL it becomes 2.7 G, which overflows, goes negative, and memcpy writes before the buffer.
The minimal fix: widen the multiplication to size_t:
67 src = G_incr_void_ptr(src, (size_t)eltLength * offsSrc);
68 dst = G_incr_void_ptr(dst, (size_t)eltLength * offsDst);
That fixes our case: blocks of up to 2³¹ − 1 cells, which is 8 GiB of FCELL. Line 70 already casts the memcpy length the same way ((size_t)nElts * eltLength), so the fix makes lines 67–68 consistent with the line just below them. A complete fix for blocks over 2³¹ cells would also need two more changes. Both alter the public API, so they suit a separate PR: