A backdoor in xz [LWN.net]

A backdoor in xz

Posted Mar 29, 2024 20:28 UTC (Fri) by intelfx (subscriber, #130118)
In reply to: A backdoor in xz by cjwatson
Parent article: A backdoor in xz

> The only problem is that it's a pretty horrible amount of code to have to inline. Look at pid_notify_with_fds_internal

I don't think any of that code is needed. OpenSSH as patched only needs sd_listen_fds() and plain sd_notify() which _as used_ can be implemented in about 5-10 lines of C code each.

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A backdoor in xz

Posted Mar 29, 2024 20:35 UTC (Fri) by cjwatson (subscriber, #7322) [Link] (2 responses)

sd_notify calls pid_notify_with_fds_internal, though? But if there's a reasonably standard inlined C reimplementation that covers all the necessary API surface, I'd definitely consider it.

A backdoor in xz

Posted Mar 30, 2024 1:12 UTC (Sat) by zdzichu (subscriber, #17118) [Link]

That's the details of a specific implementation. Actual protocol is simple. Env var contains a socket path, you write a short string text string to it. Really few lines of code.

A backdoor in xz

Posted Mar 30, 2024 6:50 UTC (Sat) by intelfx (subscriber, #130118) [Link]

> But if there's a reasonably standard inlined C reimplementation that covers all the necessary API surface, I'd definitely consider it.

Yep, that's why I tried to emphasize "as used". The implementation you see is shared between several mostly-disjoint users (e. g. it is also used to communicate with hypervisors via vsock) and also implements other features of this ad-hoc protocol (such as fd passing) which are not used in openssh.

The usage in openssh (to signal readiness) is covered by writing a fixed, static text string into an AF_UNIX datagram socket pointed to by the $NOTIFY_SOCKET variable.