C++: Fix CWE-119 memcpy tests #20876
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sizeof(pointer) only gives the pointer size, not the buffer size, so use explicit 10/20 lengths in tests.cpp and update OverflowBuffer.expected to accept the resulting memcpy diagnostics. Signed-off-by: Mingjie Shen <[email protected]>
jketema
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Nov 21, 2025
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Thanks for noticing this. We would like to be a bit more explicit, see below. Otherwise this looks fine.
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| memcpy(bigbuffer, smallbuffer, 10); // GOOD | ||
| memcpy(bigbuffer, smallbuffer, 20); // BAD: over-read | ||
| memcpy(smallbuffer, bigbuffer, 10); // GOOD | ||
| memcpy(smallbuffer, bigbuffer, 20); // BAD: over-write |
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We would prefer the following here:
Suggested change
| memcpy(bigbuffer, smallbuffer, 10); // GOOD | |
| memcpy(bigbuffer, smallbuffer, 20); // BAD: over-read | |
| memcpy(smallbuffer, bigbuffer, 10); // GOOD | |
| memcpy(smallbuffer, bigbuffer, 20); // BAD: over-write | |
| memcpy(bigbuffer, smallbuffer, sizeof(char) * 10); // GOOD | |
| memcpy(bigbuffer, smallbuffer, sizeof(char) * 20); // BAD: over-read | |
| memcpy(smallbuffer, bigbuffer, sizeof(char) * 10); // GOOD | |
| memcpy(smallbuffer, bigbuffer, sizeof(char) * 20); // BAD: over-write |
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| memcpy(bigbuffer, smallbuffer, 10); // GOOD | ||
| memcpy(bigbuffer, smallbuffer, 20); // BAD: over-read | ||
| memcpy(smallbuffer, bigbuffer, 10); // GOOD | ||
| memcpy(smallbuffer, bigbuffer, 20); // BAD: over-write |
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We would prefer the following:
Suggested change
| memcpy(bigbuffer, smallbuffer, 10); // GOOD | |
| memcpy(bigbuffer, smallbuffer, 20); // BAD: over-read | |
| memcpy(smallbuffer, bigbuffer, 10); // GOOD | |
| memcpy(smallbuffer, bigbuffer, 20); // BAD: over-write | |
| memcpy(bigbuffer, smallbuffer, sizeof(char[10])); // GOOD | |
| memcpy(bigbuffer, smallbuffer, sizeof(char[20])); // BAD: over-read | |
| memcpy(smallbuffer, bigbuffer, sizeof(char[10])); // GOOD | |
| memcpy(smallbuffer, bigbuffer, sizeof(char[20])); // BAD: over-write |
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sizeof(pointer) only gives the pointer size, not the buffer size, so use explicit 10/20 lengths in tests.cpp and update OverflowBuffer.expected to accept the resulting memcpy diagnostics.