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Chapter 4.3. - Calling strlen on NULL #46

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pixelshot91 opened this issue Feb 21, 2024 · 1 comment · May be fixed by #47
Open

Chapter 4.3. - Calling strlen on NULL #46

pixelshot91 opened this issue Feb 21, 2024 · 1 comment · May be fixed by #47

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@pixelshot91
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In the C code here https://highassurance.rs/chp4/attack_1.html#breaking-temporal-memory-safety-value-validity,

    char* greeting = get_greeting();
    size_t greeting_len = strlen(greeting); // Excludes null byte  <-- Calling `strlen` before checking that greeting is non null
    if (greeting != NULL) {

We call strlen before checking that greeting is non-null, resulting in Undefined Behavior
@tnballo
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tnballo commented Feb 21, 2024

Ah, awesome catch! Would you like to PR a fix (probably move the strlen call into the if body)?

We could also add a sentence or two to the text noting that the strlen call must happen after the NULL check to avoid UB. Feels worth calling out in retrospect!

@pixelshot91 pixelshot91 linked a pull request Feb 22, 2024 that will close this issue
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chap4: c_snippet: move strlen inside 'if' pixelshot91/high-assurance-rust
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@pixelshot91 @tnballo