hooks: Harden when we accept push options that change repo settings

It is possible to change some repo settings (its visibility, and
template status) via `git push` options: `-o repo.private=true`, `-o
repo.template=true`.

Previously, there weren't sufficient permission checks on these, and
anyone who could `git push` to a repository - including via an AGit
workflow! - was able to change either of these settings. To guard
against this, the pre-receive hook will now check if either of these
options are present, and if so, will perform additional permission
checks to ensure that these can only be set by a repository owner or
an administrator. Additionally, changing these settings is disabled for
forks, even for the fork's owner.

There's still a case where the owner of a repository can change the
visibility of it, and it will not propagate to forks (it propagates to
forks when changing the visibility via the API), but that's an
inconsistency, not a security issue.

Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>

routers/private/hook_pre_receive.go

@@ -101,6 +101,57 @@ func (ctx *preReceiveContext) AssertCreatePullRequest() bool {
 	return true
 }
 
+func (ctx *preReceiveContext) canChangeSettings() bool {
+	if !ctx.loadPusherAndPermission() {
+		return false
+	}
+
+	perm, err := access_model.GetUserRepoPermission(ctx, ctx.Repo.Repository, ctx.user)
+	if err != nil {
+		return false
+	}
+	if !perm.IsOwner() && !perm.IsAdmin() {
+		return false
+	}
+
+	if ctx.Repo.Repository.IsFork {
+		return false
+	}
+
+	return true
+}
+
+func (ctx *preReceiveContext) assertChangeSettings() bool {
+	opts := web.GetForm(ctx).(*private.HookOptions)
+
+	if len(opts.GitPushOptions) == 0 {
+		return true
+	}
+
+	_, hasPrivateOpt := opts.GitPushOptions[private.GitPushOptionRepoPrivate]
+	_, hasTemplateOpt := opts.GitPushOptions[private.GitPushOptionRepoTemplate]
+
+	if !hasPrivateOpt && !hasTemplateOpt {
+		// If neither `repo.private` nor `repo.template` is present in
+		// the push options, we're good to go without further permission
+		// checking.
+		return true
+	}
+
+	// Either `repo.private` or `repo.template` is among the push options,
+	// do some permission checks.
+	if !ctx.canChangeSettings() {
+		if ctx.Written() {
+			return false
+		}
+		ctx.JSON(http.StatusForbidden, private.Response{
+			UserMsg: "Permission denied for changing repo settings.",
+		})
+		return false
+	}
+	return true
+}
+
 // HookPreReceive checks whether a individual commit is acceptable
 func HookPreReceive(ctx *gitea_context.PrivateContext) {
 	opts := web.GetForm(ctx).(*private.HookOptions)
@@ -111,6 +162,10 @@ func HookPreReceive(ctx *gitea_context.PrivateContext) {
 		opts:           opts,
 	}
 
+	if !ourCtx.assertChangeSettings() {
+		return
+	}
+
 	// Iterate across the provided old commit IDs
 	for i := range opts.OldCommitIDs {
 		oldCommitID := opts.OldCommitIDs[i]

tests/integration/git_push_test.go

@@ -8,29 +8,20 @@ import (
 	"testing"
 
 	"code.gitea.io/gitea/models/db"
+	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
-	"code.gitea.io/gitea/modules/git"
+	repo_module "code.gitea.io/gitea/modules/repository"
 	repo_service "code.gitea.io/gitea/services/repository"
 
 	"github.com/stretchr/testify/require"
 )
 
-func TestGitPush(t *testing.T) {
-	onGiteaRun(t, testGitPush)
+func TestOptionsGitPush(t *testing.T) {
+	onGiteaRun(t, testOptionsGitPush)
 }
 
-func testGitPush(t *testing.T, u *url.URL) {
-	t.Run("Push branch with options", func(t *testing.T) {
-		runTestGitPush(t, u, func(t *testing.T, gitPath string) {
-			branchName := "branch-with-options"
-			doGitCreateBranch(gitPath, branchName)(t)
-			doGitPushTestRepository(gitPath, "origin", branchName, "-o", "repo.private=true", "-o", "repo.template=true")(t)
-		})
-	})
-}
-
-func runTestGitPush(t *testing.T, u *url.URL, gitOperation func(t *testing.T, gitPath string)) {
+func testOptionsGitPush(t *testing.T, u *url.URL) {
 	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
 	repo, err := repo_service.CreateRepository(db.DefaultContext, user, user, repo_service.CreateRepoOptions{
 		Name:          "repo-to-push",
@@ -46,22 +37,59 @@ func runTestGitPush(t *testing.T, u *url.URL, gitOperation func(t *testing.T, gi
 
 	doGitInitTestRepository(gitPath)(t)
 
-	oldPath := u.Path
-	oldUser := u.User
-	defer func() {
-		u.Path = oldPath
-		u.User = oldUser
-	}()
 	u.Path = repo.FullName() + ".git"
 	u.User = url.UserPassword(user.LowerName, userPassword)
-
 	doGitAddRemote(gitPath, "origin", u)(t)
 
-	gitRepo, err := git.OpenRepository(git.DefaultContext, gitPath)
+	{
+		// owner sets private & template to true via push options
+		branchName := "branch1"
+		doGitCreateBranch(gitPath, branchName)(t)
+		doGitPushTestRepository(gitPath, "origin", branchName, "-o", "repo.private=true", "-o", "repo.template=true")(t)
+		repo, err := repo_model.GetRepositoryByOwnerAndName(db.DefaultContext, user.Name, "repo-to-push")
 		require.NoError(t, err)
-	defer gitRepo.Close()
+		require.True(t, repo.IsPrivate)
+		require.True(t, repo.IsTemplate)
+	}
 
-	gitOperation(t, gitPath)
+	{
+		// owner sets private & template to false via push options
+		branchName := "branch2"
+		doGitCreateBranch(gitPath, branchName)(t)
+		doGitPushTestRepository(gitPath, "origin", branchName, "-o", "repo.private=false", "-o", "repo.template=false")(t)
+		repo, err = repo_model.GetRepositoryByOwnerAndName(db.DefaultContext, user.Name, "repo-to-push")
+		require.NoError(t, err)
+		require.False(t, repo.IsPrivate)
+		require.False(t, repo.IsTemplate)
+	}
+
+	{
+		// create a collaborator with write access
+		collaborator := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 5})
+		u.User = url.UserPassword(collaborator.LowerName, userPassword)
+		doGitAddRemote(gitPath, "collaborator", u)(t)
+		repo, err := repo_model.GetRepositoryByOwnerAndName(db.DefaultContext, user.Name, "repo-to-push")
+		require.NoError(t, err)
+		repo_module.AddCollaborator(db.DefaultContext, repo, collaborator)
+	}
+
+	{
+		// collaborator with write access is allowed to push
+		branchName := "branch3"
+		doGitCreateBranch(gitPath, branchName)(t)
+		doGitPushTestRepository(gitPath, "collaborator", branchName)(t)
+	}
+
+	{
+		// collaborator with write access fails to change private & template via push options
+		branchName := "branch4"
+		doGitCreateBranch(gitPath, branchName)(t)
+		doGitPushTestRepositoryFail(gitPath, "collaborator", branchName, "-o", "repo.private=true", "-o", "repo.template=true")(t)
+		repo, err = repo_model.GetRepositoryByOwnerAndName(db.DefaultContext, user.Name, "repo-to-push")
+		require.NoError(t, err)
+		require.False(t, repo.IsPrivate)
+		require.False(t, repo.IsTemplate)
+	}
 
 	require.NoError(t, repo_service.DeleteRepositoryDirectly(db.DefaultContext, user, user.ID, repo.ID))
 }