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Linux IPC hardening: lantern-group authorization #338

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eb37895
linux ipc auth via lantern group
atavism Feb 23, 2026
26a30d3
ipc control-group helper cleanup
atavism Feb 24, 2026
39fab57
code review updates
atavism Feb 24, 2026
9e8541c
Merge remote-tracking branch 'origin/main' into atavism/linux-test
atavism Mar 24, 2026
777aa45
code review updates
atavism Mar 24, 2026
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40 changes: 39 additions & 1 deletion vpn/ipc/conn_nonwindows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -84,10 +84,48 @@ func getConnPeer(conn net.Conn) (p usr, err error) {
}

uidStr := strconv.FormatUint(uint64(uid), 10)
peer, err := getPeerUser(uid, uidStr)
if err != nil {
return p, err
}
return peer, nil
}

func linuxUserInControlGroup(u *user.User) (bool, error) {
group, err := user.LookupGroup(controlGroup)
if err != nil {
return false, fmt.Errorf("lookup %s group: %w", controlGroup, err)
}
Comment on lines +94 to +98
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Copilot AI Feb 24, 2026

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conn_nonwindows.go is built on Android/iOS (//go:build !windows), but the newly added Linux group-check code depends on controlGroupGID() / controlGroupGIDInt() which are only defined in control_group_nonwindows.go (!android && !ios && !windows). This will cause Android/iOS builds of package ipc to fail with an undefined symbol error. Consider moving the Linux-specific helpers (linuxUserInControlGroup and the runtime.GOOS == "linux" branch) into a //go:build linux file, or widening/providing stub implementations for controlGroupGID* on mobile builds.

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@myleshorton myleshorton Feb 26, 2026

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The above sounds right to me!

gids, err := u.GroupIds()
if err != nil {
return false, fmt.Errorf("lookup groups for %s: %w", u.Username, err)
}
for _, gid := range gids {
if gid == group.Gid {
return true, nil
}
}
return false, nil
}
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func getPeerUser(uid uint32, uidStr string) (usr, error) {
u, err := user.LookupId(uidStr)
if err != nil {
return p, fmt.Errorf("lookup user id %v: %w", uid, err)
return usr{}, fmt.Errorf("lookup user id %v: %w", uid, err)
}

if runtime.GOOS == "linux" {
inControlGroup, err := linuxUserInControlGroup(u)
if err != nil {
return usr{}, err
}
return usr{
uid: uidStr,
uname: u.Username,
inControlGroup: inControlGroup,
}, nil
}

return usr{
uid: uidStr,
uname: u.Username,
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2 changes: 1 addition & 1 deletion vpn/ipc/middlewares.go
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Original file line number Diff line number Diff line change
Expand Up @@ -61,5 +61,5 @@ func authPeer(next http.Handler) http.Handler {
}

func peerCanAccess(peer usr) bool {
return peer.isAdmin
return peer.isAdmin || peer.inControlGroup
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Copilot AI Feb 24, 2026

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This change unintentionally blocks root from accessing the IPC API on Linux: getPeerUser() doesn’t set isAdmin on Linux, and root typically isn’t in the lantern group, so peerCanAccess() will return false even though the socket permissions allow root. Consider explicitly allowing uid 0 (e.g., peer.uid == \"0\") or setting isAdmin for uid 0 in the Linux path.

Suggested change
return peer.isAdmin || peer.inControlGroup
return peer.isAdmin || peer.inControlGroup || peer.uid == "0"

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@myleshorton myleshorton Feb 26, 2026

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Sounds right!

}
16 changes: 14 additions & 2 deletions vpn/ipc/socket.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,8 @@ import (
"strconv"
)

const controlGroup = "lantern"

// use a var so it can be overridden in tests
var _socketPath = "/var/run/lantern/lanternd.sock"

Expand All @@ -25,8 +27,18 @@ func socketPath() string {
func setPermissions() error {
path := socketPath()
if runtime.GOOS == "linux" {
// we'll check if user is sudoer to restrict access
return os.Chmod(socketPath(), 0666)
group, err := user.LookupGroup(controlGroup)
if err != nil {
return fmt.Errorf("lookup %s group: %w", controlGroup, err)
}
gid, err := strconv.Atoi(group.Gid)
if err != nil {
return fmt.Errorf("convert %s gid %s: %w", controlGroup, group.Gid, err)
}
if err := os.Chown(path, 0, gid); err != nil {
return fmt.Errorf("chown %s: %w", path, err)
}
return os.Chmod(path, 0660)
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}

// chown admin group and let the OS restrict access
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7 changes: 4 additions & 3 deletions vpn/ipc/usr.go
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Expand Up @@ -10,9 +10,10 @@ import (
type usrKey struct{}

type usr struct {
uid string
uname string
isAdmin bool
uid string
uname string
isAdmin bool
inControlGroup bool
}

func contextWithUsr(ctx context.Context, u usr) context.Context {
Expand Down
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