Skip to content

fix(sshutil): add mutex to TOFU known_hosts to prevent race condition #644

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
ArangoGutierrez merged 1 commit into from
Feb 13, 2026
Merged

fix(sshutil): add mutex to TOFU known_hosts to prevent race condition #644

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 9 additions & 0 deletions pkg/sshutil/tofu.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,16 @@ import (
"os"
"path/filepath"
"strings"
"sync"

"golang.org/x/crypto/ssh"
)

// tofuMu serialises access to the known_hosts file so that concurrent SSH
// connections (e.g. during multi-node cluster provisioning) do not race on the
// read-then-write.
var tofuMu sync.Mutex

// TOFUHostKeyCallback returns an ssh.HostKeyCallback implementing a
// Trust-On-First-Use (TOFU) pattern for SSH host key verification. On first
// connection to a host, the key is recorded in a holodeck-specific known_hosts
Expand All @@ -34,6 +40,9 @@ import (
// a potential MITM attack — is rejected with an error.
func TOFUHostKeyCallback() ssh.HostKeyCallback {
return func(hostname string, remote net.Addr, key ssh.PublicKey) error {
tofuMu.Lock()
defer tofuMu.Unlock()

Comment on lines +43 to +45
Copy link

Copilot AI Feb 12, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The new global mutex is intended to fix a concurrency race, but there’s no test exercising concurrent calls to the callback. Adding a unit test that runs many goroutines calling this callback against the same temp known_hosts path (and asserting the file ends up with a single correct entry and no errors) would prevent regressions and would fail under -race if the locking is removed/broken.

Copilot generated this review using guidance from repository custom instructions.
cacheBase, err := os.UserCacheDir()
if err != nil {
return fmt.Errorf("cannot determine cache directory for TOFU host keys: %w", err)
Expand Down
Loading