refactor: use secret.Do instead of memcall - #137
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Previously, ssh-tpm-agent would leak the buffer containing the passphrase as the buffer wrapper was dropped. This is hard to fix as the underlying tpm keyfile library expects a normal go byte slice as the passphrase, not an externally managed memory segment. This changes the signing module to wrap the passphrase fetching code so the buffer can also be returned, allowing it to be freed when present. It also leaves the option for the askpass machinery to provide similar buffers in the future.
Use the new (experimental) `secret.Do` in Go 1.26 instead of relying on memcall to protect the passphrase of the user. This requires a forced GC after signing to ensure all relevant buffers are removed from memory, or the passphrase can be trivially found in a coredump. But I don't believe this guarantees the GC will clear the buffer.
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Use the new (experimental)
secret.Doin Go 1.26 instead of relying on memcall to protect the passphrase of the user.This requires a forced GC after signing to ensure all relevant buffers are removed from memory, or the passphrase can be trivially found in a coredump. But I don't believe this guarantees the GC will clear the buffer.
Based on #135 to show the difference easily to both master and that branch. I do still think we should keep memcall for
mlock. But after using my ssh-tpm-key a few times, I could confirm no passphrase was in the generated core dump. But a core dump mid-signing would still likely leak the passphrase.Marked as a draft since Github workflow will need adjusting to enable the experimental Go feature.