Include a NUL byte in the message returned by wasm_trap_message(). #1947
Conversation
nlewycky
requested review from
Hywan,
jubianchi and
MarkMcCaskey
as code owners
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wasm.h has this to say: so I'd guess that wasm_message_t should be NUL terminated but wasm_name_t may not be. In practice it came up in wasm-c-api/examples/start.cc which prints out a string by pointer: Since it's using a pointer with no length, operator<< calls strlen() to find the end of the string which in turn reads off the end. |
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That's good to know! I'd expect this to be a more widespread issue, affecting everywhere |
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bors r+ |
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👍 |
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This PR was actually incorrect. |
`wasm_trap_new` expects a `wasm_message_t`. It's a type alias to `wasm_name_t` with the exception that it represents a null-terminated string. When calling `wasm_trap_new`, no check was present to ensure the string was well-formed. That's a first issue. But in the best scenario, the string was correctly formed and was null-terminated. This string was transformed to a Rust `String` —with the null byte!— and passed to `RuntimeError`. Then in `wasm_trap_message`, another null byte was pushed at the end of the message. It's been introduced in wasmerio#1947. It results in a doubly-null-terminated string, which is incorrect. This patch does the following: 1. It checks that the string given to `wasm_trap_new` contains a null-terminated string or not, and will act accordingly. Note that it's possible to pass a non-null-terminated string, and it will still work because this detail is vicious. The idea is to get a well-formed `RuntimeError` in anycase. * If no null byte is found, the string is passed to `RuntimeError` as a valid Rust string, * If a null byte is found at the end of the string, a new string is passed to `RuntimeError` but without the final null byte, * If a null byte is found but not at the end, it's considered as an error, * If the string contains invalid UTF-8 bytes, it's considered as an error. 2. It updates `wasm_trap_message` to always add a null byte at the end of the returned owned string. 3. It adds test cases when passing a null-terminated or a non-null-terminated string to `wasm_trap_new` and to compare the results to `wasm_trap_message`.
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