fix(codec): return InvalidVarint instead of panic on excess continuation bytes#3271
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erenyegit wants to merge 1 commit intocommonwarexyz:mainfrom
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fix(codec): return InvalidVarint instead of panic on excess continuation bytes#3271erenyegit wants to merge 1 commit intocommonwarexyz:mainfrom
erenyegit wants to merge 1 commit intocommonwarexyz:mainfrom
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…ion bytes Decoder::feed could panic when fed more continuation bytes than fit in the target type (e.g. 6+ bytes for u32). Replaced unwrap() with proper Error::InvalidVarint return for malformed or adversarial input.
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| } | ||
| let err = decoder.feed(0x80).unwrap_err(); | ||
| assert!(matches!(err, Error::InvalidVarint(4))); | ||
| } |
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Test doesn't exercise the new checked_sub code path
Low Severity
The test decoder_rejects_excess_continuation_bytes never exercises the new checked_sub → ok_or guard. Because feed returns an error before incrementing bits_read (line 155 is unreached on error), bits_read stays at 28 after the 5th feed. The 6th feed still computes remaining_bits = 4 via a successful checked_sub, and the error comes from the existing overflow check at lines 140–144, not the new guard. The new defensive code has no test coverage.
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Problem
varint::Decoder::feedcould panic when the decoder received more continuation bytes than fit in the target type. For example, forDecoder::<u32>(max 5 bytes), feeding a 6th byte with the continuation bit set causedmax_bits.checked_sub(self.bits_read)to returnNone, and.unwrap()panicked.This is a robustness issue: malformed or adversarial input could crash the process instead of returning an error.
Solution
Replace the
.unwrap()with.ok_or(Error::InvalidVarint(U::SIZE))?, so excess continuation bytes produce a properError::InvalidVarintinstead of a panic. The decoder already uses this error variant for other invalid varint cases.Testing
decoder_rejects_excess_continuation_bytesthat feeds 6 continuation bytes toDecoder::<u32>and asserts anInvalidVarint(4)error is returned.cargo test -p commonware-codecpasses (110 tests + doc tests).