golang/go

x/sys/unix: KeyctlString() panics for key types that can legally contain "no payload at all

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#54,498 opened on Aug 17, 2022

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Description

What version of Go are you using (go version)?

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

What did you do?

https://go.dev/play/p/60ZtM3V4_Io

This program needs to run on Linux - and not in a dev/play container (where the keyctl syscall is masked). On a VM, it panics thus:

This is because unix.KeyctlString() assumes key lengths are always > 0 (and it can "strip the trailing null byte") at the very least. But It is possible for certain key types (keyrings, notably) to be "legally empty", and a unix.KeyctlBuffer() on these will correctly return zero for the length..

What did you expect to see?

Not panic. Return"", nil (zero-length content, no error). This would be trivially achievable by changing https://github.com/golang/sys/blob/master/unix/syscall_linux.go#L1392,

if err != nil {
        return "", err
}

into:

if err != nil || length == 0 {
...

What did you see instead?

Panic in go standard lib. Completely unnecessary.

Contributor guide

Research direction
Inspect the KeyctlString function in the unix package at the line mentioned in the issue, and add a condition to handle zero length key payloads before stripping trailing null bytes.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80