Overlapping Encoder Slices

ID

go.overlapping_encode_slices

Severity

high

Remediation Complexity

simple

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Go

Tags

correctness, reliability

Description

Reports an encoder call Encode(dst, src) where dst and src are the same expression, so the destination and source share memory. Applies to the encoders in encoding/hex, encoding/ascii85, encoding/base32 and encoding/base64.

Rationale

These encoders write more than one output byte per input byte. When the destination and source reference the same memory, the encoder overwrites source bytes before it has finished reading them, producing corrupted output. The destination must be a distinct buffer.

func fn() {
    a := make([]byte, 8)
    hex.Encode(a, a) // FLAW — overlapping dst and src corrupts the output
}

Remediation

Pass a separate destination buffer, sized for the encoded length, instead of reusing the source slice.

References