Guard constructor argSize against codesize underflow#494
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axic
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Jun 24, 2026
| // (codesize() < programSize) would make sub() wrap to ~2^256, | ||
| // corrupting the free-memory pointer and codecopy length. | ||
| // TODO: use require with proper error | ||
| if lt(codesize(), programSize) { revert(0, 0) } |
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In the case a truncated bytecode is sent, the codeCopy below would try to write into infinitely large memory pointer, effectively causing and out-of-gas error.
There's no easy way to test this, as testrunner sends the entire code.
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Does make me wonder, this check probably should go into startBody before copy_arguments_for_constructor, so it is run even if no arguments.
In copy_arguments_for_constructor, argSize = sub(codesize(), programSize) underflows to ~2^256 when init-code is truncated (codesize() < programSize), corrupting the free-memory pointer and codecopy length. Add an explicit lt(codesize(), programSize) check that reverts before the subtraction. Co-Authored-By: Alex Beregszaszi <alex@rtfs.hu>
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In copy_arguments_for_constructor, argSize = sub(codesize(), programSize) underflows to ~2^256 when init-code is truncated (codesize() < programSize), corrupting the free-memory pointer and codecopy length. Add an explicit lt(codesize(), programSize) check that reverts before the subtraction.