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SSH connection hand-over #38545
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SSH connection hand-over #38545
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68b5f58
WIP: Connection handover
espadolini 226decc
Add a test, make socket names shorter
espadolini 4b4eb5a
Encode token hashes with base 64
espadolini 71cabe8
Document temporary directory creation more
espadolini 56c74ec
Minor cleanups
espadolini cfbec5f
fix non-unix builds
espadolini 63794f5
Expand handover tests
espadolini 50e4b60
use PrivateDirMode constant
espadolini 0608afd
name changes: {start,create}HandoverListener
espadolini 44c62fa
SSHServerWrapper godocs
espadolini fa81fa6
avoid passing cleanupDelay in a context
espadolini a2924f2
name change: retainNonConnectableSockets
espadolini aefbc45
add a reference for the logic in the Accept loop
espadolini 3f14a35
get rid of handover_other, windows supports AF_UNIX
espadolini da39989
don't log "not exist" errors when cleaning up
espadolini 347ca06
grammar and wording
espadolini f434358
retain multiple errors in cleanup, up to a limit
espadolini 006bd9e
Log non-ok-network-error errors from ProxyConn
espadolini File filter
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// Teleport | ||
// Copyright (C) 2024 Gravitational, Inc. | ||
// | ||
// This program is free software: you can redistribute it and/or modify | ||
// it under the terms of the GNU Affero General Public License as published by | ||
// the Free Software Foundation, either version 3 of the License, or | ||
// (at your option) any later version. | ||
// | ||
// This program is distributed in the hope that it will be useful, | ||
// but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
// GNU Affero General Public License for more details. | ||
// | ||
// You should have received a copy of the GNU Affero General Public License | ||
// along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
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package resumption | ||
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import ( | ||
"context" | ||
"crypto/sha256" | ||
"encoding/base64" | ||
"errors" | ||
"io" | ||
"net" | ||
"net/netip" | ||
"os" | ||
"path/filepath" | ||
"strings" | ||
"syscall" | ||
"time" | ||
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"github.com/gravitational/trace" | ||
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"github.com/gravitational/teleport" | ||
"github.com/gravitational/teleport/lib/multiplexer" | ||
"github.com/gravitational/teleport/lib/utils" | ||
) | ||
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const sockSuffix = ".sock" | ||
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func sockPath(dataDir string, token resumptionToken) string { | ||
hash := sha256.Sum256(token[:]) | ||
// unix domain sockets are limited to 108 or 104 characters, so the full | ||
// sha256 hash is a bit too much (64 bytes in hex or 44 in b64); truncating | ||
// the hash to 128 bits still gives us more than enough headroom to just | ||
// assume that we'll have no collisions (a probability of one in a | ||
// quintillion with 26 billion concurrent connections) | ||
return filepath.Join(dataDir, "handover", base64.RawURLEncoding.EncodeToString(hash[:16])+sockSuffix) | ||
} | ||
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func sockDir(dataDir string) string { | ||
return filepath.Join(dataDir, "handover") | ||
} | ||
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var errNoDataDir error = &trace.NotFoundError{Message: "data dir not configured"} | ||
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func (r *SSHServerWrapper) attemptHandover(conn *multiplexer.Conn, token resumptionToken) { | ||
handoverConn, err := r.dialHandover(token) | ||
if err != nil { | ||
if trace.IsNotFound(err) { | ||
r.log.Debug("Resumable connection not found or already deleted.") | ||
_, _ = conn.Write([]byte{notFoundServerExchangeTag}) | ||
return | ||
} | ||
r.log.WithError(err).Error("Error while connecting to handover socket.") | ||
return | ||
} | ||
defer handoverConn.Close() | ||
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var remoteIP netip.Addr | ||
if t, _ := conn.RemoteAddr().(*net.TCPAddr); t != nil { | ||
remoteIP, _ = netip.AddrFromSlice(t.IP) | ||
} | ||
remoteIP16 := remoteIP.As16() | ||
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if _, err := handoverConn.Write(remoteIP16[:]); err != nil { | ||
if !utils.IsOKNetworkError(err) { | ||
r.log.WithError(err).Error("Error while forwarding remote address to handover socket.") | ||
} | ||
return | ||
} | ||
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r.log.Debug("Forwarding resuming connection to handover socket.") | ||
if err := utils.ProxyConn(context.Background(), conn, handoverConn); err != nil && !utils.IsOKNetworkError(err) { | ||
r.log.WithError(err).Debug("Finished forwarding resuming connection to handover socket.") | ||
} | ||
} | ||
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func (r *SSHServerWrapper) dialHandover(token resumptionToken) (net.Conn, error) { | ||
if r.dataDir == "" { | ||
return nil, trace.Wrap(errNoDataDir) | ||
} | ||
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c, err := net.DialTimeout("unix", sockPath(r.dataDir, token), time.Second) | ||
if err != nil { | ||
return nil, trace.ConvertSystemError(err) | ||
} | ||
return c, nil | ||
} | ||
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func (r *SSHServerWrapper) startHandoverListener(ctx context.Context, token resumptionToken, entry *connEntry) error { | ||
l, err := r.createHandoverListener(token) | ||
if err != nil { | ||
return trace.Wrap(err) | ||
} | ||
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go r.runHandoverListener(l, entry) | ||
context.AfterFunc(ctx, func() { _ = l.Close() }) | ||
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return nil | ||
} | ||
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func (r *SSHServerWrapper) createHandoverListener(token resumptionToken) (net.Listener, error) { | ||
if r.dataDir == "" { | ||
return nil, trace.Wrap(errNoDataDir) | ||
} | ||
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_ = os.MkdirAll(sockDir(r.dataDir), teleport.PrivateDirMode) | ||
l, err := net.Listen("unix", sockPath(r.dataDir, token)) | ||
if err != nil { | ||
return nil, trace.ConvertSystemError(err) | ||
} | ||
return l, nil | ||
} | ||
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func (r *SSHServerWrapper) runHandoverListener(l net.Listener, entry *connEntry) { | ||
defer l.Close() | ||
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var tempDelay time.Duration | ||
for { | ||
// the logic for this Accept loop is copied from [net/http.Server] | ||
c, err := l.Accept() | ||
if err == nil { | ||
tempDelay = 0 | ||
go r.handleHandoverConnection(c, entry) | ||
continue | ||
} | ||
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if tempErr, ok := err.(interface{ Temporary() bool }); !ok || !tempErr.Temporary() { | ||
if !utils.IsOKNetworkError(err) { | ||
r.log.WithError(err).Warn("Accept error in handover listener.") | ||
} | ||
return | ||
} | ||
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tempDelay = max(5*time.Millisecond, min(2*tempDelay, time.Second)) | ||
r.log.WithError(err).WithField("delay", tempDelay).Warn("Temporary accept error in handover listener, continuing after delay.") | ||
time.Sleep(tempDelay) | ||
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} | ||
} | ||
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func (r *SSHServerWrapper) handleHandoverConnection(conn net.Conn, entry *connEntry) { | ||
defer conn.Close() | ||
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var remoteIP16 [16]byte | ||
if _, err := io.ReadFull(conn, remoteIP16[:]); err != nil { | ||
if !utils.IsOKNetworkError(err) { | ||
r.log.WithError(err).Error("Error while reading remote address from handover socket.") | ||
} | ||
return | ||
} | ||
remoteIP := netip.AddrFrom16(remoteIP16).Unmap() | ||
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r.resumeConnection(entry, conn, remoteIP) | ||
} | ||
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// HandoverCleanup deletes handover sockets that were left over from previous | ||
// runs of Teleport that failed to clean up after themselves (because of an | ||
// uncatchable signal or a system crash). It will exhaustively clean up the | ||
// current left over sockets, so it's sufficient to call it once per process. | ||
func (r *SSHServerWrapper) HandoverCleanup(ctx context.Context) error { | ||
const cleanupDelay = time.Second | ||
return trace.Wrap(r.handoverCleanup(ctx, cleanupDelay)) | ||
} | ||
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func (r *SSHServerWrapper) handoverCleanup(ctx context.Context, cleanupDelay time.Duration) error { | ||
if r.dataDir == "" { | ||
return nil | ||
} | ||
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dir := sockDir(r.dataDir) | ||
entries, err := os.ReadDir(dir) | ||
if err != nil { | ||
if errors.Is(err, os.ErrNotExist) { | ||
return nil | ||
} | ||
return trace.ConvertSystemError(err) | ||
} | ||
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paths := make([]string, 0, len(entries)) | ||
for _, entry := range entries { | ||
if strings.HasSuffix(entry.Name(), sockSuffix) { | ||
paths = append(paths, filepath.Join(dir, entry.Name())) | ||
} | ||
} | ||
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paths, firstErr := retainNonConnectableSockets(ctx, paths) | ||
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if len(paths) < 1 { | ||
return trace.Wrap(firstErr) | ||
} | ||
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// unix domain sockets exist on disk between bind() and listen() but | ||
// connecting before listen() results in ECONNREFUSED, so we just wait a | ||
// little bit before testing them again; the first check lets us be done | ||
// with the check immediately in the happy case where there's no | ||
// unconnectable sockets | ||
r.log.WithField("sockets", len(paths)).Debug("Found some unconnectable handover sockets, waiting before checking them again.") | ||
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select { | ||
case <-ctx.Done(): | ||
return trace.NewAggregate(firstErr, ctx.Err()) | ||
case <-time.After(cleanupDelay): | ||
} | ||
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paths, secondErr := retainNonConnectableSockets(ctx, paths) | ||
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if len(paths) < 1 { | ||
r.log.Debug("Found no unconnectable handover sockets after waiting.") | ||
return trace.NewAggregate(firstErr, secondErr) | ||
} | ||
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r.log.WithField("sockets", len(paths)).Info("Cleaning up some non-connectable handover sockets from old Teleport instances.") | ||
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errs := []error{firstErr, secondErr} | ||
for _, path := range paths { | ||
if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) { | ||
if len(errs) < 10 { | ||
errs = append(errs, trace.ConvertSystemError(err)) | ||
} | ||
} | ||
} | ||
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return trace.NewAggregate(errs...) | ||
} | ||
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// retainNonConnectableSockets attempts to connect to the given UNIX domain | ||
// sockets, returning all and only the ones that exist and that refuse the | ||
// connection. | ||
func retainNonConnectableSockets(ctx context.Context, paths []string) ([]string, error) { | ||
var d net.Dialer | ||
var errs []error | ||
filtered := paths[:0] | ||
for _, path := range paths { | ||
c, err := d.DialContext(ctx, "unix", path) | ||
if err == nil { | ||
_ = c.Close() | ||
continue | ||
} | ||
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if errors.Is(err, os.ErrNotExist) { | ||
continue | ||
} | ||
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if errors.Is(err, syscall.ECONNREFUSED) { | ||
filtered = append(filtered, path) | ||
continue | ||
} | ||
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if len(errs) < 10 { | ||
errs = append(errs, trace.ConvertSystemError(err)) | ||
} | ||
} | ||
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return filtered, trace.NewAggregate(errs...) | ||
} |
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I'm comfortable leaving the remote IP slice as all zeroes and let the server decide if that's good enough or not, rather than prohibit it in the client side.