KITFORMA · EDITORIAL GUIDE
How do I prevent count-times-size overflow before malloc?
KitForma editorial guide. An allocation can be too small even when malloc succeeds if the byte-count calculation wrapped before the call. Subsequent element writes then exceed the allocation.
Step-by-step guidance
An allocation can be too small even when malloc succeeds if the byte-count calculation wrapped before the call. Subsequent element writes then exceed the allocation.
Before computing
count * sizeof *items, require count <= SIZE_MAX / sizeof *items, with the appropriate standard headers. Also enforce a realistic application limit, because a representable allocation can still exhaust memory. Define the zero-count case explicitly and check allocation failure.
Test boundary counts through a calculation-only helper rather than actually requesting huge memory. Sanitizers can reveal downstream corruption, but prevention belongs before allocation. Never assume a 64-bit build makes attacker-controlled size arithmetic safe.Sources and verification
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