SSH connections, kept by the people who own them
An agent chat will act on a machine you choose, so this is the screen where you choose it. User-owned like a note, not admin-owned like a connection: these are somebody's own machines and somebody's own keys, and "anyone in this group may log in to my server" is a different feature with a different blast radius. services/sharing.py is deliberately not involved either -- sharing grants reading, and a host somebody else can read is a host they can log in to. Trust on first use, made explicit rather than assumed. Adding a host does not connect to it. Check looks at its key and shows you the fingerprint; nothing is sent until you accept, because get_server_host_key completes the key exchange and stops -- no username, no credential. Accepting pins it, and a host that later presents a different key is refused with the reason rather than quietly trusted. Moving a profile to another host or port forgets the pin, since a key belongs to the machine it came from. Four asyncssh defaults are actively wrong here and all four are passed explicitly: every LLeMbas user shares one unix account, so `known_hosts` would be a shared trust store, `client_keys` would authenticate one person with another's key, `config` would let a ProxyCommand redirect the connection, and `agent_path` would silently use $SSH_AUTH_SOCK. There is a test for exactly that, and it needs no server. Files go over SFTP rather than through a shell. The SSH exec protocol carries one command *string* that the far side parses, with no argv form at all, so a model-supplied path in a command line is unavoidably a quoting problem. Over SFTP a path is a path. Chat gains its kind, connection, project directory and mode; the first three are fixed once a chat has a message, because a transcript whose earlier turns ran somewhere else is not one conversation. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Jaroslav Beneš
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"""SSH connections, kept by the people who own them.
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Not an admin screen. These are somebody's own machines and somebody's own keys,
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so the pages sit beside the library rather than under `/admin` -- an
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administrator decides only whether the feature exists at all.
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Trust on first use, made explicit. Adding a host does not connect to it; the
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**Check** button looks at its key, shows the fingerprint, and waits. Only when
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that is accepted is the key pinned, and only then will anything authenticate.
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`asyncssh.get_server_host_key` completes the key exchange and stops, so a host
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that has not been accepted is never offered a username, let alone a credential.
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"""
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from __future__ import annotations
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import logging
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from datetime import UTC, datetime
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from fastapi import APIRouter, Depends, HTTPException, Request, Response, status
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from fastapi.responses import RedirectResponse
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from sqlalchemy import select
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from lembas.api.deps import Db, RequiredUser, require_permission
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from lembas.api.pages import sidebar_context
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from lembas.db.models import AUTH_METHODS, AUTH_PASSWORD, SshProfile
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from lembas.services import settings_store
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from lembas.services.agent import ssh as ssh_service
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from lembas.services.agent.base import ExecError
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from lembas.services.crypto import UNCHANGED_SENTINEL, decrypt, keep_or_replace, mask
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from lembas.web.templating import render
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log = logging.getLogger(__name__)
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router = APIRouter(
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dependencies=[Depends(require_permission("agent.ssh"))], tags=["agents"]
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)
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def _profile(db: Db, user: RequiredUser, profile_id: str) -> SshProfile:
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"""One profile belonging to this person.
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Ownership is the whole authorisation. `sharing.py` is deliberately not
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involved: it grants reading, and a host somebody else can read is a host
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they can log in to.
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"""
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profile = db.get(SshProfile, profile_id)
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if profile is None or profile.owner_id != user.id:
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raise HTTPException(status.HTTP_404_NOT_FOUND, "That connection no longer exists.")
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return profile
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def _owned(db: Db, user_id: str) -> list[SshProfile]:
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return list(
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db.scalars(
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select(SshProfile).where(SshProfile.owner_id == user_id).order_by(SshProfile.name)
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)
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)
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def _back(message: str = "") -> Response:
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target = f"/agents?saved={message}" if message else "/agents"
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return RedirectResponse(target, status_code=status.HTTP_303_SEE_OTHER)
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def _number(raw, *, default: int, low: int, high: int) -> int:
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text = str(raw or "").strip()
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if not text.isdigit():
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return default
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return min(max(int(text), low), high)
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def _apply(profile: SshProfile, form) -> None:
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"""Copy a submitted form onto a profile.
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Checkboxes are read by key presence: FastAPI cannot tell `x=` from an absent
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`x`, and an absent one is exactly what an unticked box sends.
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"""
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profile.name = str(form.get("name") or "").strip()[:120]
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profile.host = str(form.get("host") or "").strip()[:255]
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profile.username = str(form.get("username") or "").strip()[:120]
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profile.port = _number(form.get("port"), default=22, low=1, high=65535)
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profile.connect_timeout = _number(form.get("connect_timeout"), default=15, low=3, high=120)
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profile.default_dir = str(form.get("default_dir") or "").strip()[:500]
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method = str(form.get("auth") or "").strip()
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profile.auth = method if method in AUTH_METHODS else profile.auth
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profile.enabled = "enabled" in form
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def _detail(
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request: Request,
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db: Db,
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user: RequiredUser,
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profile: SshProfile,
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*,
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is_new: bool,
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error: str = "",
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saved: str = "",
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):
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# The user is passed rather than read off the profile: a draft has never
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# been attached to a session, so `profile.owner` is None on the one page
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# that most needs a sidebar.
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return render(
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request,
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"agents/detail.html",
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{
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**sidebar_context(db, user),
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"profile": profile,
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"is_new": is_new,
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"error": error,
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"saved": saved,
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"unchanged": UNCHANGED_SENTINEL,
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"masked_password": mask(decrypt(profile.password_encrypted))
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if profile.password_encrypted
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else "",
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"has_key": bool(profile.private_key_encrypted),
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"problem": ssh_service.available(),
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},
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)
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@router.get("/agents")
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async def agents_page(request: Request, db: Db, user: RequiredUser, saved: str = ""):
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return render(
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request,
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"agents/index.html",
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{
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**sidebar_context(db, user),
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"profiles": _owned(db, user.id),
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"saved": saved,
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"problem": ssh_service.available(),
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"enabled": bool(settings_store.agents(db).get("enabled")),
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},
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)
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# Registered before /{profile_id}: FastAPI matches in registration order, so
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# with the parameterised route first "new" is captured as an id. This has been
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# a bug once already, in /admin/models.
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@router.get("/agents/new")
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async def new_profile_page(request: Request, db: Db, user: RequiredUser):
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draft = SshProfile(
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owner_id=user.id, name="", host="", username="", port=22, connect_timeout=15, enabled=True
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)
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return _detail(request, db, user, draft, is_new=True)
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@router.post("/api/agents")
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async def create_profile(request: Request, db: Db, user: RequiredUser) -> Response:
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form = await request.form()
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profile = SshProfile(owner_id=user.id)
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_apply(profile, form)
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if problem := _problem(db, profile, user.id):
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return _detail(request, db, user, profile, is_new=True, error=problem)
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profile.password_encrypted = keep_or_replace(str(form.get("password") or ""), "")
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profile.private_key_encrypted = keep_or_replace(str(form.get("private_key") or ""), "")
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profile.key_passphrase_encrypted = keep_or_replace(str(form.get("key_passphrase") or ""), "")
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db.add(profile)
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db.commit()
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log.info("%s added ssh profile %s", user.email, profile.name)
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return RedirectResponse(
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f"/agents/{profile.id}?saved=Added+{profile.name}.+Check+it+to+confirm+its+fingerprint.",
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status_code=status.HTTP_303_SEE_OTHER,
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)
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def _problem(db: Db, profile: SshProfile, owner_id: str, *, existing_id: str = "") -> str:
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if not profile.name:
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return "A connection needs a name."
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if not profile.host:
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return "A connection needs a host."
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if not profile.username:
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return "A connection needs a username to log in as."
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clash = db.scalar(
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select(SshProfile).where(
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SshProfile.owner_id == owner_id, SshProfile.name == profile.name
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)
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)
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if clash is not None and clash.id != existing_id:
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return f"You already have a connection called “{profile.name}”."
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return ""
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@router.get("/agents/{profile_id}")
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async def profile_page(
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request: Request, db: Db, user: RequiredUser, profile_id: str, saved: str = ""
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):
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profile = _profile(db, user, profile_id)
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return _detail(request, db, user, profile, is_new=False, saved=saved)
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@router.post("/api/agents/{profile_id}/check")
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async def check_profile(request: Request, db: Db, user: RequiredUser, profile_id: str):
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"""Look at the host's key, and connect if it has already been accepted.
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Two steps in one button, because they are one question: *is this the machine
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I meant, and will it let me in?* An unseen key comes back as a fingerprint
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to accept; an accepted one is used to log in and run something harmless.
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"""
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profile = _profile(db, user, profile_id)
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try:
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line, fingerprint = await ssh_service.capture_host_key(
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profile.host, profile.port, timeout=profile.connect_timeout
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)
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except ExecError as exc:
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profile.last_error = exc.message
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profile.last_checked_at = datetime.now(UTC)
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db.commit()
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return render(
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request, "agents/_check.html", {"profile": profile, "error": exc.message}
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)
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if not profile.host_key:
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# First sight. Nothing is pinned until a person says so.
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return render(
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request,
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"agents/_check.html",
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{"profile": profile, "offer": {"line": line, "fingerprint": fingerprint}},
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)
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if line.strip() != profile.host_key.strip():
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message = (
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"This host is presenting a different key than the one you accepted. "
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"Nothing was sent to it. If you rebuilt the machine, forget the key "
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"below and check again; if you did not, stop and find out why."
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)
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profile.last_error = message
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profile.last_checked_at = datetime.now(UTC)
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db.commit()
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return render(
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request,
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"agents/_check.html",
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{
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"profile": profile,
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"error": message,
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"offer": {"line": line, "fingerprint": fingerprint, "changed": True},
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},
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)
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try:
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found = await ssh_service.check(ssh_service.spec_from(profile), profile.default_dir)
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except ExecError as exc:
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profile.last_error = exc.message
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profile.last_checked_at = datetime.now(UTC)
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db.commit()
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return render(
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request, "agents/_check.html", {"profile": profile, "error": exc.message}
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)
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profile.last_error = ""
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profile.last_checked_at = datetime.now(UTC)
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profile.server_info = {"system": found.get("system", ""), "cwd": found.get("cwd", "")}
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db.commit()
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return render(request, "agents/_check.html", {"profile": profile, "found": found})
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@router.post("/api/agents/{profile_id}/accept")
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async def accept_host_key(request: Request, db: Db, user: RequiredUser, profile_id: str):
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"""Pin the fingerprint that was just shown.
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The line is re-fetched rather than taken from the form: a value that made a
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round trip through a browser is not what should end up as the thing every
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future connection is checked against.
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"""
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profile = _profile(db, user, profile_id)
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try:
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line, fingerprint = await ssh_service.capture_host_key(
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profile.host, profile.port, timeout=profile.connect_timeout
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)
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except ExecError as exc:
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return render(request, "agents/_check.html", {"profile": profile, "error": exc.message})
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profile.host_key = line
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profile.host_fingerprint = fingerprint
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profile.last_error = ""
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db.commit()
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log.info("%s pinned host key for %s (%s)", user.email, profile.name, fingerprint)
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return render(
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request,
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"agents/_check.html",
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{"profile": profile, "accepted": fingerprint},
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)
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@router.post("/api/agents/{profile_id}/forget")
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async def forget_host_key(request: Request, db: Db, user: RequiredUser, profile_id: str):
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profile = _profile(db, user, profile_id)
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profile.host_key = ""
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profile.host_fingerprint = ""
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db.commit()
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return render(request, "agents/_check.html", {"profile": profile, "forgotten": True})
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@router.post("/api/agents/{profile_id}/delete")
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async def delete_profile(db: Db, user: RequiredUser, profile_id: str) -> Response:
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profile = _profile(db, user, profile_id)
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name = profile.name
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db.delete(profile)
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db.commit()
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log.info("%s deleted ssh profile %s", user.email, name)
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return _back(f"Deleted {name}.")
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@router.post("/api/agents/{profile_id}")
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async def update_profile(request: Request, db: Db, user: RequiredUser, profile_id: str):
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profile = _profile(db, user, profile_id)
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form = await request.form()
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before = (profile.host, profile.port)
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_apply(profile, form)
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if problem := _problem(db, profile, user.id, existing_id=profile.id):
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db.rollback()
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return _detail(
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request, db, user, _profile(db, user, profile_id), is_new=False, error=problem
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)
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profile.password_encrypted = keep_or_replace(
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str(form.get("password") or ""), profile.password_encrypted
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)
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profile.private_key_encrypted = keep_or_replace(
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str(form.get("private_key") or ""), profile.private_key_encrypted
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)
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profile.key_passphrase_encrypted = keep_or_replace(
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str(form.get("key_passphrase") or ""), profile.key_passphrase_encrypted
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)
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if profile.auth == AUTH_PASSWORD:
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profile.private_key_encrypted = ""
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profile.key_passphrase_encrypted = ""
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# A pinned key belongs to a host and a port. Moving either means this is a
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# different machine until proven otherwise, and silently keeping the old
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# key would be the one mistake this whole mechanism exists to prevent.
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if (profile.host, profile.port) != before and profile.host_key:
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profile.host_key = ""
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profile.host_fingerprint = ""
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log.info("%s moved ssh profile %s; its host key was forgotten", user.email, profile.name)
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db.commit()
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return RedirectResponse(
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f"/agents/{profile.id}?saved=Saved.", status_code=status.HTTP_303_SEE_OTHER
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)
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Reference in New Issue
Block a user