[kernel] Perform sbrk address wrap check #2134
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Yet another fix - signed arithmetic address wrap check is now performed in the kernel. This check was previously in v7malloc but not in standard malloc.
Address wrap could occur in malloc/sbrk when the heap break is at a high address, and a large allocation request occurs that overflows the 16-bit process heap break address when calculating the new break address. This was previously not checked for an would result in the break set to a low address, corrupting data.
A message "SBRK FAIL, OUT OF HEAP (address wrap)" is now displayed, and the allocation denied, which will end up with malloc safely returning NULL.