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Currently, we use PermitRead/PermitWrite/PermitCert permission flags to determine which operations are allowed for a LocalAPI client. These checks are performed when localapi.Handler handles a request. Additionally, certain operations (e.g., changing the serve config) requires the connected user to be a local admin. This approach is inherently racey and is subject to TOCTOU issues. We consider it to be more critical on Windows environments, which are inherently multi-user, and therefore we prevent more than one OS user from connecting and utilizing the LocalBackend at the same time. However, the same type of issues is also applicable to other platforms when switching between profiles that have different OperatorUser values in ipn.Prefs. We'd like to allow more than one Windows user to connect, but limit what they can see and do based on their access rights on the device (e.g., an local admin or not) and to the currently active LoginProfile (e.g., owner/operator or not), while preventing TOCTOU issues on Windows and other platforms. Therefore, we'd like to pass an actor from the LocalAPI to the LocalBackend to represent the user performing the operation. The LocalBackend, or the profileManager down the line, will then check the actor's access rights to perform a given operation on the device and against the current (and/or the target) profile. This PR does not change the current permission model in any way, but it introduces the concept of an actor and includes some preparatory work to pass it around. Temporarily, the ipnauth.Actor interface has methods like IsLocalSystem and IsLocalAdmin, which are only relevant to the current permission model. It also lacks methods that will actually be used in the new model. We'll be adding these gradually in the next PRs and removing the deprecated methods and the Permit* flags at the end of the transition. Updates tailscale/corp#18342 Signed-off-by: Nick Khyl <nickk@tailscale.com>
48 lines
1.9 KiB
Go
48 lines
1.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package ipnauth
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import (
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"tailscale.com/ipn"
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)
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// Actor is any actor using the [ipnlocal.LocalBackend].
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//
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// It typically represents a specific OS user, indicating that an operation
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// is performed on behalf of this user, should be evaluated against their
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// access rights, and performed in their security context when applicable.
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type Actor interface {
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// UserID returns an OS-specific UID of the user represented by the receiver,
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// or "" if the actor does not represent a specific user on a multi-user system.
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// As of 2024-08-27, it is only used on Windows.
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UserID() ipn.WindowsUserID
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// Username returns the user name associated with the receiver,
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// or "" if the actor does not represent a specific user.
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Username() (string, error)
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// IsLocalSystem reports whether the actor is the Windows' Local System account.
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//
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// Deprecated: this method exists for compatibility with the current (as of 2024-08-27)
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// permission model and will be removed as we progress on tailscale/corp#18342.
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IsLocalSystem() bool
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// IsLocalAdmin reports whether the actor has administrative access to the
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// local machine, for whatever that means with respect to the current OS.
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//
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// The operatorUID is only used on Unix-like platforms and specifies the ID
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// of a local user (in the os/user.User.Uid string form) who is allowed to
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// operate tailscaled without being root or using sudo.
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//
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// Deprecated: this method exists for compatibility with the current (as of 2024-08-27)
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// permission model and will be removed as we progress on tailscale/corp#18342.
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IsLocalAdmin(operatorUID string) bool
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}
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// ActorCloser is an optional interface that might be implemented by an [Actor]
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// that must be closed when done to release the resources.
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type ActorCloser interface {
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// Close releases resources associated with the receiver.
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Close() error
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}
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