Add "Allow edits from maintainer" feature (#18002)

Adds a feature [like GitHub has](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork) (step 7).
If you create a new PR from a forked repo, you can select (and change later, but only if you are the PR creator/poster) the "Allow edits from maintainers" option.
Then users with write access to the base branch get more permissions on this branch:
* use the update pull request button
* push directly from the command line (`git push`)
* edit/delete/upload files via web UI
* use related API endpoints

You can't merge PRs to this branch with this enabled, you'll need "full" code write permissions.

This feature has a pretty big impact on the permission system. I might forgot changing some things or didn't find security vulnerabilities. In this case, please leave a review or comment on this PR.

Closes #17728

Co-authored-by: 6543 <6543@obermui.de>

29 files changed, 359 insertions, 60 deletions

diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index ba8ca85bc8..9e46791ec6 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -61,6 +61,7 @@ type Version struct {
 // update minDBVersion accordingly
 var migrations = []Migration{
 	// Gitea 1.5.0 ends at v69
+
 	// v70 -> v71
 	NewMigration("add issue_dependencies", addIssueDependencies),
 	// v71 -> v72
@@ -380,6 +381,8 @@ var migrations = []Migration{
 	NewMigration("Create ForeignReference table", createForeignReferenceTable),
 	// v212 -> v213
 	NewMigration("Add package tables", addPackageTables),
+	// v213 -> v214
+	NewMigration("Add allow edits from maintainers to PullRequest table", addAllowMaintainerEdit),
 }
 
 // GetCurrentDBVersion returns the current db version
diff --git a/models/migrations/v213.go b/models/migrations/v213.go
new file mode 100644
index 0000000000..b1dbf98d1e
--- /dev/null
+++ b/models/migrations/v213.go
@@ -0,0 +1,18 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+func addAllowMaintainerEdit(x *xorm.Engine) error {
+	// PullRequest represents relation between pull request and repositories.
+	type PullRequest struct {
+		AllowMaintainerEdit bool `xorm:"NOT NULL DEFAULT false"`
+	}
+
+	return x.Sync2(new(PullRequest))
+}
diff --git a/models/pull.go b/models/pull.go
index e04263af9f..437b202d3f 100644
--- a/models/pull.go
+++ b/models/pull.go
@@ -69,15 +69,16 @@ type PullRequest struct {
 	Issue   *Issue `xorm:"-"`
 	Index   int64
 
-	HeadRepoID      int64                  `xorm:"INDEX"`
-	HeadRepo        *repo_model.Repository `xorm:"-"`
-	BaseRepoID      int64                  `xorm:"INDEX"`
-	BaseRepo        *repo_model.Repository `xorm:"-"`
-	HeadBranch      string
-	HeadCommitID    string `xorm:"-"`
-	BaseBranch      string
-	ProtectedBranch *ProtectedBranch `xorm:"-"`
-	MergeBase       string           `xorm:"VARCHAR(40)"`
+	HeadRepoID          int64                  `xorm:"INDEX"`
+	HeadRepo            *repo_model.Repository `xorm:"-"`
+	BaseRepoID          int64                  `xorm:"INDEX"`
+	BaseRepo            *repo_model.Repository `xorm:"-"`
+	HeadBranch          string
+	HeadCommitID        string `xorm:"-"`
+	BaseBranch          string
+	ProtectedBranch     *ProtectedBranch `xorm:"-"`
+	MergeBase           string           `xorm:"VARCHAR(40)"`
+	AllowMaintainerEdit bool             `xorm:"NOT NULL DEFAULT false"`
 
 	HasMerged      bool               `xorm:"INDEX"`
 	MergedCommitID string             `xorm:"VARCHAR(40)"`
@@ -711,6 +712,14 @@ func (pr *PullRequest) GetHeadBranchHTMLURL() string {
 	return pr.HeadRepo.HTMLURL() + "/src/branch/" + util.PathEscapeSegments(pr.HeadBranch)
 }
 
+// UpdateAllowEdits update if PR can be edited from maintainers
+func UpdateAllowEdits(ctx context.Context, pr *PullRequest) error {
+	if _, err := db.GetEngine(ctx).ID(pr.ID).Cols("allow_maintainer_edit").Update(pr); err != nil {
+		return err
+	}
+	return nil
+}
+
 // Mergeable returns if the pullrequest is mergeable.
 func (pr *PullRequest) Mergeable() bool {
 	// If a pull request isn't mergable if it's:
diff --git a/models/repo_permission.go b/models/repo_permission.go
index b4291f2362..bc31b873f2 100644
--- a/models/repo_permission.go
+++ b/models/repo_permission.go
@@ -103,6 +103,39 @@ func (p *Permission) CanWriteIssuesOrPulls(isPull bool) bool {
 	return p.CanWrite(unit.TypeIssues)
 }
 
+// CanWriteToBranch checks if the branch is writable by the user
+func (p *Permission) CanWriteToBranch(user *user_model.User, branch string) bool {
+	if p.CanWrite(unit.TypeCode) {
+		return true
+	}
+
+	if len(p.Units) < 1 {
+		return false
+	}
+
+	prs, err := GetUnmergedPullRequestsByHeadInfo(p.Units[0].RepoID, branch)
+	if err != nil {
+		return false
+	}
+
+	for _, pr := range prs {
+		if pr.AllowMaintainerEdit {
+			err = pr.LoadBaseRepo()
+			if err != nil {
+				continue
+			}
+			prPerm, err := GetUserRepoPermission(db.DefaultContext, pr.BaseRepo, user)
+			if err != nil {
+				continue
+			}
+			if prPerm.CanWrite(unit.TypeCode) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // ColorFormat writes a colored string for these Permissions
 func (p *Permission) ColorFormat(s fmt.State) {
 	noColor := log.ColorBytes(log.Reset)
@@ -160,6 +193,7 @@ func GetUserRepoPermission(ctx context.Context, repo *repo_model.Repository, use
 				perm)
 		}()
 	}
+
 	// anonymous user visit private repo.
 	// TODO: anonymous user visit public unit of private repo???
 	if user == nil && repo.IsPrivate {
diff --git a/modules/context/permission.go b/modules/context/permission.go
index 142b86faea..8dc3b3cd46 100644
--- a/modules/context/permission.go
+++ b/modules/context/permission.go
@@ -29,6 +29,16 @@ func RequireRepoWriter(unitType unit.Type) func(ctx *Context) {
 	}
 }
 
+// CanEnableEditor checks if the user is allowed to write to the branch of the repo
+func CanEnableEditor() func(ctx *Context) {
+	return func(ctx *Context) {
+		if !ctx.Repo.Permission.CanWriteToBranch(ctx.Doer, ctx.Repo.BranchName) {
+			ctx.NotFound("CanWriteToBranch denies permission", nil)
+			return
+		}
+	}
+}
+
 // RequireRepoWriterOr returns a middleware for requiring repository write to one of the unit permission
 func RequireRepoWriterOr(unitTypes ...unit.Type) func(ctx *Context) {
 	return func(ctx *Context) {
diff --git a/modules/context/repo.go b/modules/context/repo.go
index a02bb7e869..b2c9a21f8e 100644
--- a/modules/context/repo.go
+++ b/modules/context/repo.go
@@ -78,8 +78,8 @@ type Repository struct {
 }
 
 // CanEnableEditor returns true if repository is editable and user has proper access level.
-func (r *Repository) CanEnableEditor() bool {
-	return r.Permission.CanWrite(unit_model.TypeCode) && r.Repository.CanEnableEditor() && r.IsViewBranch && !r.Repository.IsArchived
+func (r *Repository) CanEnableEditor(user *user_model.User) bool {
+	return r.IsViewBranch && r.Permission.CanWriteToBranch(user, r.BranchName) && r.Repository.CanEnableEditor() && !r.Repository.IsArchived
 }
 
 // CanCreateBranch returns true if repository is editable and user has proper access level.
@@ -123,7 +123,7 @@ func (r *Repository) CanCommitToBranch(ctx context.Context, doer *user_model.Use
 
 	sign, keyID, _, err := asymkey_service.SignCRUDAction(ctx, r.Repository.RepoPath(), doer, r.Repository.RepoPath(), git.BranchPrefix+r.BranchName)
 
-	canCommit := r.CanEnableEditor() && userCanPush
+	canCommit := r.CanEnableEditor(doer) && userCanPush
 	if requireSigned {
 		canCommit = canCommit && sign
 	}
@@ -139,7 +139,7 @@ func (r *Repository) CanCommitToBranch(ctx context.Context, doer *user_model.Use
 
 	return CanCommitToBranchResults{
 		CanCommitToBranch: canCommit,
-		EditorEnabled:     r.CanEnableEditor(),
+		EditorEnabled:     r.CanEnableEditor(doer),
 		UserCanPush:       userCanPush,
 		RequireSigned:     requireSigned,
 		WillSign:          sign,
diff --git a/modules/convert/convert.go b/modules/convert/convert.go
index 3f565f76e0..bd06f4dbf4 100644
--- a/modules/convert/convert.go
+++ b/modules/convert/convert.go
@@ -41,12 +41,19 @@ func ToEmail(email *user_model.EmailAddress) *api.Email {
 func ToBranch(repo *repo_model.Repository, b *git.Branch, c *git.Commit, bp *models.ProtectedBranch, user *user_model.User, isRepoAdmin bool) (*api.Branch, error) {
 	if bp == nil {
 		var hasPerm bool
+		var canPush bool
 		var err error
 		if user != nil {
 			hasPerm, err = models.HasAccessUnit(user, repo, unit.TypeCode, perm.AccessModeWrite)
 			if err != nil {
 				return nil, err
 			}
+
+			perms, err := models.GetUserRepoPermission(db.DefaultContext, repo, user)
+			if err != nil {
+				return nil, err
+			}
+			canPush = perms.CanWriteToBranch(user, b.Name)
 		}
 
 		return &api.Branch{
@@ -56,7 +63,7 @@ func ToBranch(repo *repo_model.Repository, b *git.Branch, c *git.Commit, bp *mod
 			RequiredApprovals:   0,
 			EnableStatusCheck:   false,
 			StatusCheckContexts: []string{},
-			UserCanPush:         hasPerm,
+			UserCanPush:         canPush,
 			UserCanMerge:        hasPerm,
 		}, nil
 	}
diff --git a/modules/convert/pull.go b/modules/convert/pull.go
index 6034327a9d..a2f54270e4 100644
--- a/modules/convert/pull.go
+++ b/modules/convert/pull.go
@@ -73,6 +73,8 @@ func ToAPIPullRequest(ctx context.Context, pr *models.PullRequest, doer *user_mo
 		Created:   pr.Issue.CreatedUnix.AsTimePtr(),
 		Updated:   pr.Issue.UpdatedUnix.AsTimePtr(),
 
+		AllowMaintainerEdit: pr.AllowMaintainerEdit,
+
 		Base: &api.PRBranchInfo{
 			Name:       pr.BaseBranch,
 			Ref:        pr.BaseBranch,
diff --git a/modules/structs/pull.go b/modules/structs/pull.go
index 653091b2f4..b63b3edfd3 100644
--- a/modules/structs/pull.go
+++ b/modules/structs/pull.go
@@ -31,9 +31,10 @@ type PullRequest struct {
 	Mergeable bool `json:"mergeable"`
 	HasMerged bool `json:"merged"`
 	// swagger:strfmt date-time
-	Merged         *time.Time `json:"merged_at"`
-	MergedCommitID *string    `json:"merge_commit_sha"`
-	MergedBy       *User      `json:"merged_by"`
+	Merged              *time.Time `json:"merged_at"`
+	MergedCommitID      *string    `json:"merge_commit_sha"`
+	MergedBy            *User      `json:"merged_by"`
+	AllowMaintainerEdit bool       `json:"allow_maintainer_edit"`
 
 	Base      *PRBranchInfo `json:"base"`
 	Head      *PRBranchInfo `json:"head"`
@@ -90,6 +91,7 @@ type EditPullRequestOption struct {
 	Labels    []int64  `json:"labels"`
 	State     *string  `json:"state"`
 	// swagger:strfmt date-time
-	Deadline       *time.Time `json:"due_date"`
-	RemoveDeadline *bool      `json:"unset_due_date"`
+	Deadline            *time.Time `json:"due_date"`
+	RemoveDeadline      *bool      `json:"unset_due_date"`
+	AllowMaintainerEdit *bool      `json:"allow_maintainer_edit"`
 }
diff --git a/modules/structs/repo_file.go b/modules/structs/repo_file.go
index e2947bf7ac..135e6484cd 100644
--- a/modules/structs/repo_file.go
+++ b/modules/structs/repo_file.go
@@ -30,6 +30,11 @@ type CreateFileOptions struct {
 	Content string `json:"content"`
 }
 
+// Branch returns branch name
+func (o *CreateFileOptions) Branch() string {
+	return o.FileOptions.BranchName
+}
+
 // DeleteFileOptions options for deleting files (used for other File structs below)
 // Note: `author` and `committer` are optional (if only one is given, it will be used for the other, otherwise the authenticated user will be used)
 type DeleteFileOptions struct {
@@ -39,6 +44,11 @@ type DeleteFileOptions struct {
 	SHA string `json:"sha" binding:"Required"`
 }
 
+// Branch returns branch name
+func (o *DeleteFileOptions) Branch() string {
+	return o.FileOptions.BranchName
+}
+
 // UpdateFileOptions options for updating files
 // Note: `author` and `committer` are optional (if only one is given, it will be used for the other, otherwise the authenticated user will be used)
 type UpdateFileOptions struct {
@@ -50,6 +60,16 @@ type UpdateFileOptions struct {
 	FromPath string `json:"from_path" binding:"MaxSize(500)"`
 }
 
+// Branch returns branch name
+func (o *UpdateFileOptions) Branch() string {
+	return o.FileOptions.BranchName
+}
+
+// FileOptionInterface provides a unified interface for the different file options
+type FileOptionInterface interface {
+	Branch() string
+}
+
 // ApplyDiffPatchFileOptions options for applying a diff patch
 // Note: `author` and `committer` are optional (if only one is given, it will be used for the other, otherwise the authenticated user will be used)
 type ApplyDiffPatchFileOptions struct {
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index 5ec001b6d4..0175c8bfc8 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -1488,6 +1488,9 @@ pulls.desc = Enable pull requests and code reviews.
 pulls.new = New Pull Request
 pulls.view = View Pull Request
 pulls.compare_changes = New Pull Request
+pulls.allow_edits_from_maintainers = Allow edits from maintainers
+pulls.allow_edits_from_maintainers_desc = Users with write access to the base branch can also push to this branch
+pulls.allow_edits_from_maintainers_err = Updating failed
 pulls.compare_changes_desc = Select the branch to merge into and the branch to pull from.
 pulls.compare_base = merge into
 pulls.compare_compare = pull from
diff --git a/routers/api/v1/api.go b/routers/api/v1/api.go
index cca0f37ba1..782500e6c8 100644
--- a/routers/api/v1/api.go
+++ b/routers/api/v1/api.go
@@ -283,6 +283,15 @@ func reqRepoWriter(unitTypes ...unit.Type) func(ctx *context.APIContext) {
 	}
 }
 
+// reqRepoBranchWriter user should have a permission to write to a branch, or be a site admin
+func reqRepoBranchWriter(ctx *context.APIContext) {
+	options, ok := web.GetForm(ctx).(api.FileOptionInterface)
+	if !ok || (!ctx.Repo.CanWriteToBranch(ctx.Doer, options.Branch()) && !ctx.IsUserSiteAdmin()) {
+		ctx.Error(http.StatusForbidden, "reqRepoBranchWriter", "user should have a permission to write to this branch")
+		return
+	}
+}
+
 // reqRepoReader user should have specific read permission or be a repo admin or a site admin
 func reqRepoReader(unitType unit.Type) func(ctx *context.APIContext) {
 	return func(ctx *context.APIContext) {
@@ -1021,10 +1030,10 @@ func Routes() *web.Route {
 					m.Get("", repo.GetContentsList)
 					m.Get("/*", repo.GetContents)
 					m.Group("/*", func() {
-						m.Post("", bind(api.CreateFileOptions{}), repo.CreateFile)
-						m.Put("", bind(api.UpdateFileOptions{}), repo.UpdateFile)
-						m.Delete("", bind(api.DeleteFileOptions{}), repo.DeleteFile)
-					}, reqRepoWriter(unit.TypeCode), reqToken())
+						m.Post("", bind(api.CreateFileOptions{}), reqRepoBranchWriter, repo.CreateFile)
+						m.Put("", bind(api.UpdateFileOptions{}), reqRepoBranchWriter, repo.UpdateFile)
+						m.Delete("", bind(api.DeleteFileOptions{}), reqRepoBranchWriter, repo.DeleteFile)
+					}, reqToken())
 				}, reqRepoReader(unit.TypeCode))
 				m.Get("/signing-key.gpg", misc.SigningKey)
 				m.Group("/topics", func() {
diff --git a/routers/api/v1/repo/file.go b/routers/api/v1/repo/file.go
index d907e770ae..b8b72f95eb 100644
--- a/routers/api/v1/repo/file.go
+++ b/routers/api/v1/repo/file.go
@@ -173,8 +173,10 @@ func GetEditorconfig(ctx *context.APIContext) {
 }
 
 // canWriteFiles returns true if repository is editable and user has proper access level.
-func canWriteFiles(r *context.Repository) bool {
-	return r.Permission.CanWrite(unit.TypeCode) && !r.Repository.IsMirror && !r.Repository.IsArchived
+func canWriteFiles(ctx *context.APIContext, branch string) bool {
+	return ctx.Repo.Permission.CanWriteToBranch(ctx.Doer, branch) &&
+		!ctx.Repo.Repository.IsMirror &&
+		!ctx.Repo.Repository.IsArchived
 }
 
 // canReadFiles returns true if repository is readable and user has proper access level.
@@ -376,7 +378,7 @@ func handleCreateOrUpdateFileError(ctx *context.APIContext, err error) {
 
 // Called from both CreateFile or UpdateFile to handle both
 func createOrUpdateFile(ctx *context.APIContext, opts *files_service.UpdateRepoFileOptions) (*api.FileResponse, error) {
-	if !canWriteFiles(ctx.Repo) {
+	if !canWriteFiles(ctx, opts.OldBranch) {
 		return nil, models.ErrUserDoesNotHaveAccessToRepo{
 			UserID:   ctx.Doer.ID,
 			RepoName: ctx.Repo.Repository.LowerName,
@@ -433,7 +435,7 @@ func DeleteFile(ctx *context.APIContext) {
 	//     "$ref": "#/responses/error"
 
 	apiOpts := web.GetForm(ctx).(*api.DeleteFileOptions)
-	if !canWriteFiles(ctx.Repo) {
+	if !canWriteFiles(ctx, apiOpts.BranchName) {
 		ctx.Error(http.StatusForbidden, "DeleteFile", models.ErrUserDoesNotHaveAccessToRepo{
 			UserID:   ctx.Doer.ID,
 			RepoName: ctx.Repo.Repository.LowerName,
diff --git a/routers/api/v1/repo/patch.go b/routers/api/v1/repo/patch.go
index ae64c6efe3..6dbf979701 100644
--- a/routers/api/v1/repo/patch.go
+++ b/routers/api/v1/repo/patch.go
@@ -77,7 +77,7 @@ func ApplyDiffPatch(ctx *context.APIContext) {
 		opts.Message = "apply-patch"
 	}
 
-	if !canWriteFiles(ctx.Repo) {
+	if !canWriteFiles(ctx, apiOpts.BranchName) {
 		ctx.Error(http.StatusInternalServerError, "ApplyPatch", models.ErrUserDoesNotHaveAccessToRepo{
 			UserID:   ctx.Doer.ID,
 			RepoName: ctx.Repo.Repository.LowerName,
diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index 6b076eff8f..9517802183 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -616,6 +616,18 @@ func EditPullRequest(ctx *context.APIContext) {
 		notification.NotifyPullRequestChangeTargetBranch(ctx.Doer, pr, form.Base)
 	}
 
+	// update allow edits
+	if form.AllowMaintainerEdit != nil {
+		if err := pull_service.SetAllowEdits(ctx, ctx.Doer, pr, *form.AllowMaintainerEdit); err != nil {
+			if errors.Is(pull_service.ErrUserHasNoPermissionForAction, err) {
+				ctx.Error(http.StatusForbidden, "SetAllowEdits", fmt.Sprintf("SetAllowEdits: %s", err))
+				return
+			}
+			ctx.ServerError("SetAllowEdits", err)
+			return
+		}
+	}
+
 	// Refetch from database
 	pr, err = models.GetPullRequestByIndex(ctx.Repo.Repository.ID, pr.Index)
 	if err != nil {
diff --git a/routers/private/hook_pre_receive.go b/routers/private/hook_pre_receive.go
index ccb6933787..8824d9cc39 100644
--- a/routers/private/hook_pre_receive.go
+++ b/routers/private/hook_pre_receive.go
@@ -45,6 +45,8 @@ type preReceiveContext struct {
 	env []string
 
 	opts *private.HookOptions
+
+	branchName string
 }
 
 // CanWriteCode returns true if pusher can write code
@@ -53,7 +55,7 @@ func (ctx *preReceiveContext) CanWriteCode() bool {
 		if !ctx.loadPusherAndPermission() {
 			return false
 		}
-		ctx.canWriteCode = ctx.userPerm.CanWrite(unit.TypeCode) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
+		ctx.canWriteCode = ctx.userPerm.CanWriteToBranch(ctx.user, ctx.branchName) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
 		ctx.checkedCanWriteCode = true
 	}
 	return ctx.canWriteCode
@@ -134,13 +136,15 @@ func HookPreReceive(ctx *gitea_context.PrivateContext) {
 }
 
 func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID, refFullName string) {
+	branchName := strings.TrimPrefix(refFullName, git.BranchPrefix)
+	ctx.branchName = branchName
+
 	if !ctx.AssertCanWriteCode() {
 		return
 	}
 
 	repo := ctx.Repo.Repository
 	gitRepo := ctx.Repo.GitRepo
-	branchName := strings.TrimPrefix(refFullName, git.BranchPrefix)
 
 	if branchName == repo.DefaultBranch && newCommitID == git.EmptySHA {
 		log.Warn("Forbidden: Branch: %s is the default branch in %-v and cannot be deleted", branchName, repo)
diff --git a/routers/web/repo/compare.go b/routers/web/repo/compare.go
index 9f7bef43ef..7721507bae 100644
--- a/routers/web/repo/compare.go
+++ b/routers/web/repo/compare.go
@@ -398,6 +398,7 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 	}
 
 	ctx.Data["HeadRepo"] = ci.HeadRepo
+	ctx.Data["BaseCompareRepo"] = ctx.Repo.Repository
 
 	// Now we need to assert that the ctx.Doer has permission to read
 	// the baseRepo's code and pulls
@@ -436,6 +437,7 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 			ctx.NotFound("ParseCompareInfo", nil)
 			return nil
 		}
+		ctx.Data["CanWriteToHeadRepo"] = permHead.CanWrite(unit.TypeCode)
 	}
 
 	// If we have a rootRepo and it's different from:
diff --git a/routers/web/repo/issue.go b/routers/web/repo/issue.go
index 8e865e448f..a54ad3306b 100644
--- a/routers/web/repo/issue.go
+++ b/routers/web/repo/issue.go
@@ -1529,7 +1529,7 @@ func ViewIssue(ctx *context.Context) {
 		if ctx.IsSigned {
 			if err := pull.LoadHeadRepoCtx(ctx); err != nil {
 				log.Error("LoadHeadRepo: %v", err)
-			} else if pull.HeadRepo != nil && pull.HeadBranch != pull.HeadRepo.DefaultBranch {
+			} else if pull.HeadRepo != nil {
 				perm, err := models.GetUserRepoPermission(ctx, pull.HeadRepo, ctx.Doer)
 				if err != nil {
 					ctx.ServerError("GetUserRepoPermission", err)
@@ -1537,12 +1537,15 @@ func ViewIssue(ctx *context.Context) {
 				}
 				if perm.CanWrite(unit.TypeCode) {
 					// Check if branch is not protected
-					if protected, err := models.IsProtectedBranch(pull.HeadRepo.ID, pull.HeadBranch); err != nil {
-						log.Error("IsProtectedBranch: %v", err)
-					} else if !protected {
-						canDelete = true
-						ctx.Data["DeleteBranchLink"] = issue.Link() + "/cleanup"
+					if pull.HeadBranch != pull.HeadRepo.DefaultBranch {
+						if protected, err := models.IsProtectedBranch(pull.HeadRepo.ID, pull.HeadBranch); err != nil {
+							log.Error("IsProtectedBranch: %v", err)
+						} else if !protected {
+							canDelete = true
+							ctx.Data["DeleteBranchLink"] = issue.Link() + "/cleanup"
+						}
 					}
+					ctx.Data["CanWriteToHeadRepo"] = true
 				}
 			}
 
diff --git a/routers/web/repo/pull.go b/routers/web/repo/pull.go
index a03e16f39a..99faa54138 100644
--- a/routers/web/repo/pull.go
+++ b/routers/web/repo/pull.go
@@ -1132,14 +1132,15 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 		Content:     form.Content,
 	}
 	pullRequest := &models.PullRequest{
-		HeadRepoID: ci.HeadRepo.ID,
-		BaseRepoID: repo.ID,
-		HeadBranch: ci.HeadBranch,
-		BaseBranch: ci.BaseBranch,
-		HeadRepo:   ci.HeadRepo,
-		BaseRepo:   repo,
-		MergeBase:  ci.CompareInfo.MergeBase,
-		Type:       models.PullRequestGitea,
+		HeadRepoID:          ci.HeadRepo.ID,
+		BaseRepoID:          repo.ID,
+		HeadBranch:          ci.HeadBranch,
+		BaseBranch:          ci.BaseBranch,
+		HeadRepo:            ci.HeadRepo,
+		BaseRepo:            repo,
+		MergeBase:           ci.CompareInfo.MergeBase,
+		Type:                models.PullRequestGitea,
+		AllowMaintainerEdit: form.AllowMaintainerEdit,
 	}
 	// FIXME: check error in the case two people send pull request at almost same time, give nice error prompt
 	// instead of 500.
@@ -1411,3 +1412,31 @@ func UpdatePullRequestTarget(ctx *context.Context) {
 		"base_branch": pr.BaseBranch,
 	})
 }
+
+// SetAllowEdits allow edits from maintainers to PRs
+func SetAllowEdits(ctx *context.Context) {
+	form := web.GetForm(ctx).(*forms.UpdateAllowEditsForm)
+
+	pr, err := models.GetPullRequestByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
+	if err != nil {
+		if models.IsErrPullRequestNotExist(err) {
+			ctx.NotFound("GetPullRequestByIndex", err)
+		} else {
+			ctx.ServerError("GetPullRequestByIndex", err)
+		}
+		return
+	}
+
+	if err := pull_service.SetAllowEdits(ctx, ctx.Doer, pr, form.AllowMaintainerEdit); err != nil {
+		if errors.Is(pull_service.ErrUserHasNoPermissionForAction, err) {
+			ctx.Error(http.StatusForbidden)
+			return
+		}
+		ctx.ServerError("SetAllowEdits", err)
+		return
+	}
+
+	ctx.JSON(http.StatusOK, map[string]interface{}{
+		"allow_maintainer_edit": pr.AllowMaintainerEdit,
+	})
+}
diff --git a/routers/web/repo/view.go b/routers/web/repo/view.go
index 168927d101..86fc36fad7 100644
--- a/routers/web/repo/view.go
+++ b/routers/web/repo/view.go
@@ -579,7 +579,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 			ctx.Data["LineEscapeStatus"] = statuses
 		}
 		if !isLFSFile {
-			if ctx.Repo.CanEnableEditor() {
+			if ctx.Repo.CanEnableEditor(ctx.Doer) {
 				if lfsLock != nil && lfsLock.OwnerID != ctx.Doer.ID {
 					ctx.Data["CanEditFile"] = false
 					ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.this_file_locked")
@@ -589,7 +589,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 				}
 			} else if !ctx.Repo.IsViewBranch {
 				ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.must_be_on_a_branch")
-			} else if !ctx.Repo.CanWrite(unit_model.TypeCode) {
+			} else if !ctx.Repo.CanWriteToBranch(ctx.Doer, ctx.Repo.BranchName) {
 				ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.fork_before_edit")
 			}
 		}
@@ -629,7 +629,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 		}
 	}
 
-	if ctx.Repo.CanEnableEditor() {
+	if ctx.Repo.CanEnableEditor(ctx.Doer) {
 		if lfsLock != nil && lfsLock.OwnerID != ctx.Doer.ID {
 			ctx.Data["CanDeleteFile"] = false
 			ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.this_file_locked")
@@ -639,7 +639,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 		}
 	} else if !ctx.Repo.IsViewBranch {
 		ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.must_be_on_a_branch")
-	} else if !ctx.Repo.CanWrite(unit_model.TypeCode) {
+	} else if !ctx.Repo.CanWriteToBranch(ctx.Doer, ctx.Repo.BranchName) {
 		ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.must_have_write_access")
 	}
 }
diff --git a/routers/web/web.go b/routers/web/web.go
index 0de6f13722..22b8e7cdf3 100644
--- a/routers/web/web.go
+++ b/routers/web/web.go
@@ -574,6 +574,7 @@ func RegisterRoutes(m *web.Route) {
 
 	reqRepoAdmin := context.RequireRepoAdmin()
 	reqRepoCodeWriter := context.RequireRepoWriter(unit.TypeCode)
+	canEnableEditor := context.CanEnableEditor()
 	reqRepoCodeReader := context.RequireRepoReader(unit.TypeCode)
 	reqRepoReleaseWriter := context.RequireRepoWriter(unit.TypeReleases)
 	reqRepoReleaseReader := context.RequireRepoReader(unit.TypeReleases)
@@ -925,12 +926,12 @@ func RegisterRoutes(m *web.Route) {
 					Post(bindIgnErr(forms.EditRepoFileForm{}), repo.NewDiffPatchPost)
 				m.Combo("/_cherrypick/{sha:([a-f0-9]{7,40})}/*").Get(repo.CherryPick).
 					Post(bindIgnErr(forms.CherryPickForm{}), repo.CherryPickPost)
-			}, context.RepoRefByType(context.RepoRefBranch), repo.MustBeEditable)
+			}, repo.MustBeEditable)
 			m.Group("", func() {
 				m.Post("/upload-file", repo.UploadFileToServer)
 				m.Post("/upload-remove", bindIgnErr(forms.RemoveUploadFileForm{}), repo.RemoveUploadFileFromServer)
-			}, context.RepoRef(), repo.MustBeEditable, repo.MustBeAbleToUpload)
-		}, context.RepoMustNotBeArchived(), reqRepoCodeWriter, repo.MustBeNotEmpty)
+			}, repo.MustBeEditable, repo.MustBeAbleToUpload)
+		}, context.RepoRef(), canEnableEditor, context.RepoMustNotBeArchived(), repo.MustBeNotEmpty)
 
 		m.Group("/branches", func() {
 			m.Group("/_new", func() {
@@ -1105,6 +1106,7 @@ func RegisterRoutes(m *web.Route) {
 			m.Get("/commits", context.RepoRef(), repo.ViewPullCommits)
 			m.Post("/merge", context.RepoMustNotBeArchived(), bindIgnErr(forms.MergePullRequestForm{}), repo.MergePullRequest)
 			m.Post("/update", repo.UpdatePullRequest)
+			m.Post("/set_allow_maintainer_edit", bindIgnErr(forms.UpdateAllowEditsForm{}), repo.SetAllowEdits)
 			m.Post("/cleanup", context.RepoMustNotBeArchived(), context.RepoRef(), repo.CleanUpPullRequest)
 			m.Group("/files", func() {
 				m.Get("", context.RepoRef(), repo.SetEditorconfigIfExists, repo.SetDiffViewStyle, repo.SetWhitespaceBehavior, repo.ViewPullFiles)
diff --git a/services/forms/repo_form.go b/services/forms/repo_form.go
index 80123e9af3..f40e99a044 100644
--- a/services/forms/repo_form.go
+++ b/services/forms/repo_form.go
@@ -422,15 +422,16 @@ func (f *NewPackagistHookForm) Validate(req *http.Request, errs binding.Errors)
 
 // CreateIssueForm form for creating issue
 type CreateIssueForm struct {
-	Title       string `binding:"Required;MaxSize(255)"`
-	LabelIDs    string `form:"label_ids"`
-	AssigneeIDs string `form:"assignee_ids"`
-	Ref         string `form:"ref"`
-	MilestoneID int64
-	ProjectID   int64
-	AssigneeID  int64
-	Content     string
-	Files       []string
+	Title               string `binding:"Required;MaxSize(255)"`
+	LabelIDs            string `form:"label_ids"`
+	AssigneeIDs         string `form:"assignee_ids"`
+	Ref                 string `form:"ref"`
+	MilestoneID         int64
+	ProjectID           int64
+	AssigneeID          int64
+	Content             string
+	Files               []string
+	AllowMaintainerEdit bool
 }
 
 // Validate validates the fields
@@ -684,6 +685,11 @@ type DismissReviewForm struct {
 	Message  string
 }
 
+// UpdateAllowEditsForm form for changing if PR allows edits from maintainers
+type UpdateAllowEditsForm struct {
+	AllowMaintainerEdit bool
+}
+
 // __________       .__
 // \______   \ ____ |  |   ____ _____    ______ ____
 //  |       _// __ \|  | _/ __ \\__  \  /  ___// __ \
diff --git a/services/pull/edits.go b/services/pull/edits.go
new file mode 100644
index 0000000000..68515ec141
--- /dev/null
+++ b/services/pull/edits.go
@@ -0,0 +1,40 @@
+// Copyright 2022 The Gitea Authors.
+// All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pull
+
+import (
+	"context"
+	"errors"
+
+	"code.gitea.io/gitea/models"
+	unit_model "code.gitea.io/gitea/models/unit"
+	user_model "code.gitea.io/gitea/models/user"
+)
+
+var ErrUserHasNoPermissionForAction = errors.New("user not allowed to do this action")
+
+// SetAllowEdits allow edits from maintainers to PRs
+func SetAllowEdits(ctx context.Context, doer *user_model.User, pr *models.PullRequest, allow bool) error {
+	if doer == nil || !pr.Issue.IsPoster(doer.ID) {
+		return ErrUserHasNoPermissionForAction
+	}
+
+	if err := pr.LoadHeadRepo(); err != nil {
+		return err
+	}
+
+	permission, err := models.GetUserRepoPermission(ctx, pr.HeadRepo, doer)
+	if err != nil {
+		return err
+	}
+
+	if !permission.CanWrite(unit_model.TypeCode) {
+		return ErrUserHasNoPermissionForAction
+	}
+
+	pr.AllowMaintainerEdit = allow
+	return models.UpdateAllowEdits(ctx, pr)
+}
diff --git a/services/pull/update.go b/services/pull/update.go
index 899bee1f19..2d845e8504 100644
--- a/services/pull/update.go
+++ b/services/pull/update.go
@@ -111,11 +111,25 @@ func IsUserAllowedToUpdate(ctx context.Context, pull *models.PullRequest, user *
 		return false, false, nil
 	}
 
+	baseRepoPerm, err := models.GetUserRepoPermission(ctx, pull.BaseRepo, user)
+	if err != nil {
+		return false, false, err
+	}
+
 	mergeAllowed, err = IsUserAllowedToMerge(pr, headRepoPerm, user)
 	if err != nil {
 		return false, false, err
 	}
 
+	if pull.AllowMaintainerEdit {
+		mergeAllowedMaintainer, err := IsUserAllowedToMerge(pr, baseRepoPerm, user)
+		if err != nil {
+			return false, false, err
+		}
+
+		mergeAllowed = mergeAllowed || mergeAllowedMaintainer
+	}
+
 	return mergeAllowed, rebaseAllowed, nil
 }
 
diff --git a/templates/repo/issue/new_form.tmpl b/templates/repo/issue/new_form.tmpl
index 1089c82415..9a4548643f 100644
--- a/templates/repo/issue/new_form.tmpl
+++ b/templates/repo/issue/new_form.tmpl
@@ -235,6 +235,15 @@
 						</a>
 					{{end}}
 				</div>
+			{{if and .PageIsComparePull (not (eq .HeadRepo.FullName .BaseCompareRepo.FullName)) .CanWriteToHeadRepo}}
+				<div class="ui divider"></div>
+				<div class="inline field">
+					<div class="ui checkbox">
+						<label class="tooltip" data-content="{{.i18n.Tr "repo.pulls.allow_edits_from_maintainers_desc"}}"><strong>{{.i18n.Tr "repo.pulls.allow_edits_from_maintainers"}}</strong></label>
+						<input name="allow_maintainer_edit" type="checkbox">
+					</div>
+				</div>
+			{{end}}
 		</div>
 		<input type="hidden" name="redirect_after_creation" value="{{.redirect_after_creation}}">
 	</div>
diff --git a/templates/repo/issue/view_content/sidebar.tmpl b/templates/repo/issue/view_content/sidebar.tmpl
index e673add812..9e9bc670a0 100644
--- a/templates/repo/issue/view_content/sidebar.tmpl
+++ b/templates/repo/issue/view_content/sidebar.tmpl
@@ -667,5 +667,21 @@
 				</form>
 			</div>
 		{{end}}
+
+		{{if and .Issue.IsPull .IsIssuePoster (not .Issue.IsClosed)}}
+			{{if and (not (eq .Issue.PullRequest.HeadRepo.FullName .Issue.PullRequest.BaseRepo.FullName)) .CanWriteToHeadRepo}}
+				<div class="ui divider"></div>
+				<div class="inline field">
+					<div class="ui checkbox" id="allow-edits-from-maintainers"
+							data-url="{{.Issue.Link}}"
+							data-prompt-tip="{{.i18n.Tr "repo.pulls.allow_edits_from_maintainers_desc"}}"
+							data-prompt-error="{{.i18n.Tr "repo.pulls.allow_edits_from_maintainers_err"}}"
+						>
+						<label><strong>{{.i18n.Tr "repo.pulls.allow_edits_from_maintainers"}}</strong></label>
+						<input type="checkbox" {{if .Issue.PullRequest.AllowMaintainerEdit}}checked{{end}}>
+					</div>
+				</div>
+			{{end}}
+		{{end}}
 	</div>
 </div>
diff --git a/templates/swagger/v1_json.tmpl b/templates/swagger/v1_json.tmpl
index ea03380d43..d57a3a580b 100644
--- a/templates/swagger/v1_json.tmpl
+++ b/templates/swagger/v1_json.tmpl
@@ -14938,6 +14938,10 @@
       "description": "EditPullRequestOption options when modify pull request",
       "type": "object",
       "properties": {
+        "allow_maintainer_edit": {
+          "type": "boolean",
+          "x-go-name": "AllowMaintainerEdit"
+        },
         "assignee": {
           "type": "string",
           "x-go-name": "Assignee"
@@ -17045,6 +17049,10 @@
       "description": "PullRequest represents a pull request",
       "type": "object",
       "properties": {
+        "allow_maintainer_edit": {
+          "type": "boolean",
+          "x-go-name": "AllowMaintainerEdit"
+        },
         "assignee": {
           "$ref": "#/definitions/User"
         },
diff --git a/web_src/js/features/repo-issue.js b/web_src/js/features/repo-issue.js
index 14b1976bbb..a39a704f47 100644
--- a/web_src/js/features/repo-issue.js
+++ b/web_src/js/features/repo-issue.js
@@ -288,6 +288,39 @@ export function initRepoPullRequestMergeInstruction() {
   });
 }
 
+export function initRepoPullRequestAllowMaintainerEdit() {
+  const $checkbox = $('#allow-edits-from-maintainers');
+  if (!$checkbox.length) return;
+
+  const promptTip = $checkbox.attr('data-prompt-tip');
+  const promptError = $checkbox.attr('data-prompt-error');
+  $checkbox.popup({content: promptTip});
+  $checkbox.checkbox({
+    'onChange': () => {
+      const checked = $checkbox.checkbox('is checked');
+      let url = $checkbox.attr('data-url');
+      url += '/set_allow_maintainer_edit';
+      $checkbox.checkbox('set disabled');
+      $.ajax({url, type: 'POST',
+        data: {_csrf: csrfToken, allow_maintainer_edit: checked},
+        error: () => {
+          $checkbox.popup({
+            content: promptError,
+            onHidden: () => {
+              // the error popup should be shown only once, then we restore the popup to the default message
+              $checkbox.popup({content: promptTip});
+            },
+          });
+          $checkbox.popup('show');
+        },
+        complete: () => {
+          $checkbox.checkbox('set enabled');
+        },
+      });
+    },
+  });
+}
+
 export function initRepoIssueReferenceRepositorySearch() {
   $('.issue_reference_repository_search')
     .dropdown({
diff --git a/web_src/js/index.js b/web_src/js/index.js
index f5d72aff93..5b95a0d8ef 100644
--- a/web_src/js/index.js
+++ b/web_src/js/index.js
@@ -36,6 +36,7 @@ import {
   initRepoIssueTimeTracking,
   initRepoIssueWipTitle,
   initRepoPullRequestMergeInstruction,
+  initRepoPullRequestAllowMaintainerEdit,
   initRepoPullRequestReview,
 } from './features/repo-issue.js';
 import {
@@ -158,6 +159,7 @@ $(document).ready(() => {
   initRepoMigrationStatusChecker();
   initRepoProject();
   initRepoPullRequestMergeInstruction();
+  initRepoPullRequestAllowMaintainerEdit();
   initRepoPullRequestReview();
   initRepoRelease();
   initRepoReleaseEditor();