docs: scope the loopback bind to remote reach (#33)#35
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…he identity gate §6 called the loopback bind load-bearing without saying against whom. It bounds remote callers; locally it bounds nothing, because a TCP port is shared by every uid in the netns while herdr's socket is uid-bounded by file permissions. An agent deliberately run under another uid to contain it can therefore still drive the whole herd through the port — installing Collie silently removes that boundary. Say so, and point at the device gate, which is the one write gate that doesn't rest on "local means trusted". Also correct two claims. §6 said the owner login is asserted and other tailnet users rejected; checkAccess only rejects a *mismatching* Tailscale-User-Login and passes an absent one — safe under tailscale serve, which always injects it, and not safe behind anything that stops. The README's "reject anyone but you" had the same gap. Records that the device gate fails closed as of 0.15.0, and that device ids are proxy-asserted names rather than secrets. Reported by @simonallfrey. Fixes #33 Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
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Closes the documentation half of #33.
ARCHITECTURE.md§6 called the loopback bind load-bearing without saying against whom. It boundsremote callers; locally it bounds nothing, because a TCP port is shared by every uid in the network
namespace while herdr's socket is uid-bounded by file permissions. So an agent deliberately run under
another uid to contain it can still
curl 127.0.0.1:$COLLIE_PORTand drive any pane in the herd —installing Collie silently removes the boundary an operator running untrusted diffs is most likely to
have reached for. §6 now says that, and points at the device gate as the one write gate that doesn't
rest on "local means trusted".
Two claims also corrected:
checkAccessonlyrejects a mismatching
Tailscale-User-Loginand passes an absent one — fine undertailscale serve, which injects it on every request; not fine behind anything that stops. TheREADME's "reject anyone but you" had the same gap.
that device ids are proxy-asserted names rather than secrets.
Reported by @simonallfrey.
Doc-only — no version bump per CLAUDE.md. Anchors and fences validated.
Fixes #33
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