policy/v2: reject hosts-table aliases as SSH dst

SaaS rejects any hosts-table alias on an SSH rule dst with
`invalid dst "alias"`, irrespective of whether the alias resolves
to a single IP or a CIDR. headscale was resolving the alias through
the same path as ACL dsts and accepting the policy. Validate at the
per-SSH-rule pass so the error body matches SaaS. The existing
host-alias-as-dst sshtest_test row tested the now-rejected shape
and is dropped along with its unused commonHosts fixture.

hscontrol/policy/v2/sshtest_test.go

@@ -83,10 +83,6 @@ func sshTestNodes(users types.Users) types.Nodes {
 	}
 }
 
-// commonHosts contains every host alias the table below references
-// as an sshTests dst. Embedded in the JSON policy under "hosts".
-const commonHosts = `"hosts": { "alice-laptop": "100.64.0.1", "bob-laptop": "100.64.0.2" }`
-
 // TestRunSSHTests covers the engine's per-test outcome reporting. Each
 // row constructs a PolicyManager (whose SetPolicy sandbox also exercises
 // evaluateSSHTests) and asserts on the resulting RunSSHTests behaviour.
@@ -563,24 +559,6 @@ func TestRunSSHTests(t *testing.T) {
 			}`,
 			wantPass: true,
 		},
-		{
-			name: "host-alias-as-dst",
-			policy: `{
-				` + commonHosts + `,
-				"ssh": [{
-					"action": "accept",
-					"src":    ["bob@headscale.net"],
-					"dst":    ["alice-laptop"],
-					"users":  ["root"]
-				}],
-				"sshTests": [{
-					"src":    "bob@headscale.net",
-					"dst":    ["alice-laptop"],
-					"accept": ["root"]
-				}]
-			}`,
-			wantPass: true,
-		},
 		{
 			name: "acl-allows-tcp22-no-ssh-rule",
 			policy: `{

hscontrol/policy/v2/tailscale_ssh_data_compat_test.go

@@ -107,18 +107,6 @@ var sshRejectSkipReasons = map[string]string{
 	"ssh-e2": "domain validation: headscale has no 'associated tailnet domains' concept",
 	"ssh-malformed-user-localpart-multi-glob": "domain validation: headscale has no 'associated tailnet domains' concept (same gap as ssh-b4/d1/e1/e2)",
 
-	// HOSTS_ALIAS_AS_SSH_DST (2 tests)
-	//
-	// SaaS rejects every hosts-alias dst on an SSH rule with
-	// `invalid dst "alias"`, regardless of whether the alias resolves
-	// to a single IP or a CIDR. headscale's compileSSHPolicy resolves
-	// host aliases through the same path as ACL dsts and accepts
-	// them. Either reject hosts-aliases at SSH dst parse time to
-	// match, or document that headscale is intentionally more
-	// permissive than SaaS for SSH dsts.
-	"ssh-hosts-as-dst-single-ip":         "SaaS rejects host alias as SSH dst, headscale accepts",
-	"ssh-hosts-as-dst-multi-host-prefix": "SaaS rejects host alias as SSH dst, headscale accepts",
-
 	// NON_ASCII_TAG_NAME (1 test)
 	//
 	// SaaS rejects non-ASCII characters in tag names with

hscontrol/policy/v2/types.go

@@ -52,6 +52,7 @@ var (
 	ErrSSHAcceptEnvEmpty                  = errors.New("acceptEnv values cannot be empty")
 	ErrSSHActionMustBeSpecified           = errors.New("action must be specified")
 	ErrSSHActionInvalid                   = errors.New("is not a valid action")
+	ErrSSHDestinationHostAlias            = errors.New("invalid dst")
 )
 
 // SSH check period constants per Tailscale docs:
@@ -2579,6 +2580,13 @@ func (p *Policy) validate() error {
 				if err != nil {
 					errs = append(errs, err)
 				}
+			case *Host:
+				// SaaS rejects every hosts-table alias on an SSH
+				// dst with `invalid dst "alias"`, whether the
+				// alias resolves to a single IP or a CIDR. The
+				// equivalent ACL rule accepts the same aliases,
+				// so reject here rather than at parse time.
+				errs = append(errs, fmt.Errorf("%w %q", ErrSSHDestinationHostAlias, string(*dst)))
 			}
 		}
 

hscontrol/policy/v2/types_test.go

@@ -4660,11 +4660,25 @@ func TestSSHRuleSaaSValidation(t *testing.T) {
 				s.AcceptEnv = []string{"**"}
 			}),
 		},
+		{
+			// SaaS rejects hosts-table aliases on SSH dst with
+			// `invalid dst "srv"`. headscale validates the same
+			// regardless of whether the alias resolves to a
+			// single IP or a CIDR.
+			name: "host alias as SSH dst rejected",
+			ssh: baseSSH(func(s *SSH) {
+				s.Destinations = SSHDstAliases{hp("srv")}
+			}),
+			wantErr: ErrSSHDestinationHostAlias,
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			pol := &Policy{SSHs: []SSH{tt.ssh}}
+			pol := &Policy{
+				Hosts: Hosts{Host("srv"): Prefix(mp("100.64.0.16/32"))},
+				SSHs:  []SSH{tt.ssh},
+			}
 			err := pol.validate()
 
 			if tt.wantErr != nil {