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Ignore host key update mechanism requests #5

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Merged
un-def merged 1 commit into from
Mar 20, 2026
Merged

Ignore host key update mechanism requests #5

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40 changes: 31 additions & 9 deletions internal/sshproxy/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ import (
"fmt"
"io"
"net"
"slices"
"strconv"
"strings"
"sync"
Expand All @@ -28,6 +29,20 @@ const (
upstreamDialTimeout = time.Second * 10
)

var blacklistedGlobalRequests = []string{
// Host key update mechanism for SSH: https://www.ietf.org/archive/id/draft-miller-sshm-hostkey-update-02.html
// Reasons to blacklist:
// 1. Signature check always fail as the signed data contains session identifier, which is not the same on client
// and upstream side, since they don't talk directly but through sshproxy (there are two SSH transport sessions
// with their own unique identifiers).
// 2. Even if it worked somehow, we don't want to inflate user's known_hosts file with garbage records,
// since container host keys are ephemeral -- they are generated on dstack-runner startup (= unique for each job).
"hostkeys",
"hostkeys-00@openssh.com",
"hostkeys-prove",
"hostkeys-prove-00@openssh.com",
}

type direction string

var (
Expand Down Expand Up @@ -386,15 +401,22 @@ func bridgeGlobalRequests(ctx context.Context, dir direction, inReqs <-chan *ssh
logger := log.GetLogger(ctx).WithField("dir", dir)
for req := range inReqs {
logger := logger.WithField("type", req.Type)
logger.Trace("global request")

reply, payload, err := outConn.SendRequest(req.Type, req.WantReply, req.Payload)
if req.WantReply {
_ = req.Reply(reply, payload)
}
if slices.Contains(blacklistedGlobalRequests, req.Type) {
logger.Trace("blacklisted global request, ignoring")
if req.WantReply {
_ = req.Reply(false, nil)
}
} else {
logger.Trace("global request")
ok, payload, err := outConn.SendRequest(req.Type, req.WantReply, req.Payload)
if req.WantReply {
_ = req.Reply(ok, payload)
}

if err != nil && !isClosedError(err) {
logger.WithError(err).Error("failed to forward global request")
if err != nil && !isClosedError(err) {
logger.WithError(err).Error("failed to forward global request")
}
}
}
}
Expand Down Expand Up @@ -488,9 +510,9 @@ func bridgeChannelRequests(ctx context.Context, dir direction, inReqs <-chan *ss
logger := logger.WithField("type", req.Type)
logger.Trace("request")

reply, err := outConn.SendRequest(req.Type, req.WantReply, req.Payload)
ok, err := outConn.SendRequest(req.Type, req.WantReply, req.Payload)
if req.WantReply {
_ = req.Reply(reply, nil)
_ = req.Reply(ok, nil)
}

if err != nil && !isClosedError(err) {
Expand Down