fix(actions): allow Actions bot to push to protected branches (#38284) (#38293)

Backport #38284 by @bircni

Fixes #38278

## Problem

When branch protection matches the branch an Actions workflow pushes to,
the runner's `git push` is rejected — even though the workflow token has
`contents: write` and the same push performed with a PAT (write access)
succeeds. Disabling protection or changing the pattern so it no longer
matches makes the push work.

## Root cause

In `preReceiveBranch` (`routers/private/hook_pre_receive.go`), the "can
the doer push to this protected branch" check resolves the pusher with
`user_model.GetUserByID(ctx, ctx.opts.UserID)`. For an Actions push the
user ID is `-2` (the virtual `ActionsUserID`), which has no database
row, so the lookup fails. Even past that, `CanUserPush` →
`HasAccessUnit`/whitelist membership cannot evaluate a virtual user and
returns `false`. As a result the Actions bot was rejected on every
matching protected branch, despite the earlier `assertCanWriteRef`
already confirming the token's code-write via
`GetActionsUserRepoPermission`.

This was inconsistent: a PAT with identical write access passed the
exact same check.

## Fix

Evaluate the Actions bot against its already-computed token permission
instead of a user lookup, mirroring the existing
`IsUserMergeWhitelisted` pattern:

- Add `CanActionsUserPush` / `CanActionsUserForcePush` on
`ProtectedBranch`, which take the precomputed `access_model.Permission`.
- Allow the push when push is enabled, **no** push whitelist is
enforced, and the token has code-write.
- Keep the bot blocked when a whitelist is enforced — it cannot be added
to one, so it must use a pull request. This preserves the whitelist as a
real security boundary.

Force-push, signed-commit and protected-file-path checks are untouched.

Signed-off-by: bircni <bircni@icloud.com>
Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/private/hook_pre_receive.go

@@ -31,9 +31,7 @@ import (
 type preReceiveContext struct {
 	*gitea_context.PrivateContext
 
-	// loadedPusher indicates that where the following information are loaded
-	loadedPusher        bool
-	user                *user_model.User // it's the org user if a DeployKey is used
+	user                *user_model.User // the "pusher", it's the org user if a DeployKey is used
 	userPerm            access_model.Permission
 	deployKeyAccessMode perm_model.AccessMode
 
@@ -53,10 +51,7 @@ type preReceiveContext struct {
 
 func (ctx *preReceiveContext) canWriteCodeUnit() bool {
 	if ctx.canWriteCodeUnitCached == nil {
-		var canWrite bool
-		if ctx.loadPusherAndPermission() {
-			canWrite = ctx.userPerm.CanWrite(unit.TypeCode) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
-		}
+		canWrite := ctx.userPerm.CanWrite(unit.TypeCode) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
 		ctx.canWriteCodeUnitCached = &canWrite
 	}
 	return *ctx.canWriteCodeUnitCached
@@ -91,9 +86,6 @@ func (ctx *preReceiveContext) assertCanWriteRef(refFullName git.RefName) bool {
 // CanCreatePullRequest returns true if pusher can create pull requests
 func (ctx *preReceiveContext) CanCreatePullRequest() bool {
 	if !ctx.checkedCanCreatePullRequest {
-		if !ctx.loadPusherAndPermission() {
-			return false
-		}
 		ctx.canCreatePullRequest = ctx.userPerm.CanRead(unit.TypePullRequests)
 		ctx.checkedCanCreatePullRequest = true
 	}
@@ -124,6 +116,10 @@ func HookPreReceive(ctx *gitea_context.PrivateContext) {
 		opts:           opts,
 	}
 
+	if !ourCtx.loadPusherAndPermission() {
+		return // if error occurs, loadPusherAndPermission had written the error response
+	}
+
 	// Iterate across the provided old commit IDs
 	for i := range opts.OldCommitIDs {
 		oldCommitID := opts.OldCommitIDs[i]
@@ -281,18 +277,10 @@ func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID string, r
 			canPush = !changedProtectedfiles && protectBranch.CanPush && (!protectBranch.EnableWhitelist || protectBranch.WhitelistDeployKeys)
 		}
 	} else {
-		user, err := user_model.GetUserByID(ctx, ctx.opts.UserID)
-		if err != nil {
-			log.Error("Unable to GetUserByID for commits from %s to %s in %-v: %v", oldCommitID, newCommitID, repo, err)
-			ctx.JSON(http.StatusInternalServerError, private.Response{
-				Err: fmt.Sprintf("Unable to GetUserByID for commits from %s to %s: %v", oldCommitID, newCommitID, err),
-			})
-			return
-		}
 		if isForcePush {
-			canPush = !changedProtectedfiles && protectBranch.CanUserForcePush(ctx, user)
+			canPush = !changedProtectedfiles && protectBranch.CanUserForcePush(ctx, ctx.user)
 		} else {
-			canPush = !changedProtectedfiles && protectBranch.CanUserPush(ctx, user)
+			canPush = !changedProtectedfiles && protectBranch.CanUserPush(ctx, ctx.user)
 		}
 	}
 
@@ -354,12 +342,6 @@ func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID string, r
 			return
 		}
 
-		// although we should have called `loadPusherAndPermission` before, here we call it explicitly again because we need to access ctx.user below
-		if !ctx.loadPusherAndPermission() {
-			// if error occurs, loadPusherAndPermission had written the error response
-			return
-		}
-
 		// Now check if the user is allowed to merge PRs for this repository
 		// Note: we can use ctx.perm and ctx.user directly as they will have been loaded above
 		allowedMerge, err := pull_service.IsUserAllowedToMerge(ctx, pr, ctx.userPerm, ctx.user)
@@ -499,10 +481,6 @@ func generateGitEnv(opts *private.HookOptions) (env []string) {
 
 // loadPusherAndPermission returns false if an error occurs, and it writes the error response
 func (ctx *preReceiveContext) loadPusherAndPermission() bool {
-	if ctx.loadedPusher {
-		return true
-	}
-
 	if ctx.opts.UserID == user_model.ActionsUserID {
 		taskID := ctx.opts.ActionsTaskID
 		ctx.user = user_model.NewActionsUserWithTaskID(taskID)
@@ -555,7 +533,5 @@ func (ctx *preReceiveContext) loadPusherAndPermission() bool {
 		}
 		ctx.deployKeyAccessMode = deployKey.Mode
 	}
-
-	ctx.loadedPusher = true
 	return true
 }

routers/private/hook_pre_receive_test.go

@@ -52,7 +52,6 @@ func TestPreReceiveCanWriteCodePerBranch(t *testing.T) {
 	mockCtx, _ := contexttest.MockPrivateContext(t, "/")
 	ctx := &preReceiveContext{
 		PrivateContext: mockCtx,
-		loadedPusher:   true,
 		user:           maintainer,
 		userPerm:       headPerm,
 	}