Clean-up HookPreReceive and restore functionality for pushing non-standard refs (#16705)

* Clean-up HookPreReceive and restore functionality for pushing non-standard refs

There was an inadvertent breaking change in #15629 meaning that notes refs and other
git extension refs will be automatically rejected.

Further following #14295 and #15629 the pre-recieve hook code is untenably long and
too complex.

This PR refactors the hook code and removes the incorrect forced rejection of
non-standard refs.

Fix #16688

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/private/hook_verification.go

@@ -0,0 +1,122 @@
+// Copyright 2021 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 private includes all internal routes. The package name internal is ideal but Golang is not allowed, so we use private as package name instead.
+package private
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"io"
+	"os"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+)
+
+// _________                        .__  __
+// \_   ___ \  ____   _____   _____ |__|/  |_
+// /    \  \/ /  _ \ /     \ /     \|  \   __\
+// \     \___(  <_> )  Y Y  \  Y Y  \  ||  |
+//  \______  /\____/|__|_|  /__|_|  /__||__|
+//         \/             \/      \/
+// ____   ____           .__  _____.__               __  .__
+// \   \ /   /___________|__|/ ____\__| ____ _____ _/  |_|__| ____   ____
+//  \   Y   // __ \_  __ \  \   __\|  |/ ___\\__  \\   __\  |/  _ \ /    \
+//   \     /\  ___/|  | \/  ||  |  |  \  \___ / __ \|  | |  (  <_> )   |  \
+//    \___/  \___  >__|  |__||__|  |__|\___  >____  /__| |__|\____/|___|  /
+//               \/                        \/     \/                    \/
+//
+// This file contains commit verification functions for refs passed across in hooks
+
+func verifyCommits(oldCommitID, newCommitID string, repo *git.Repository, env []string) error {
+	stdoutReader, stdoutWriter, err := os.Pipe()
+	if err != nil {
+		log.Error("Unable to create os.Pipe for %s", repo.Path)
+		return err
+	}
+	defer func() {
+		_ = stdoutReader.Close()
+		_ = stdoutWriter.Close()
+	}()
+
+	// This is safe as force pushes are already forbidden
+	err = git.NewCommand("rev-list", oldCommitID+"..."+newCommitID).
+		RunInDirTimeoutEnvFullPipelineFunc(env, -1, repo.Path,
+			stdoutWriter, nil, nil,
+			func(ctx context.Context, cancel context.CancelFunc) error {
+				_ = stdoutWriter.Close()
+				err := readAndVerifyCommitsFromShaReader(stdoutReader, repo, env)
+				if err != nil {
+					log.Error("%v", err)
+					cancel()
+				}
+				_ = stdoutReader.Close()
+				return err
+			})
+	if err != nil && !isErrUnverifiedCommit(err) {
+		log.Error("Unable to check commits from %s to %s in %s: %v", oldCommitID, newCommitID, repo.Path, err)
+	}
+	return err
+}
+
+func readAndVerifyCommitsFromShaReader(input io.ReadCloser, repo *git.Repository, env []string) error {
+	scanner := bufio.NewScanner(input)
+	for scanner.Scan() {
+		line := scanner.Text()
+		err := readAndVerifyCommit(line, repo, env)
+		if err != nil {
+			log.Error("%v", err)
+			return err
+		}
+	}
+	return scanner.Err()
+}
+
+func readAndVerifyCommit(sha string, repo *git.Repository, env []string) error {
+	stdoutReader, stdoutWriter, err := os.Pipe()
+	if err != nil {
+		log.Error("Unable to create pipe for %s: %v", repo.Path, err)
+		return err
+	}
+	defer func() {
+		_ = stdoutReader.Close()
+		_ = stdoutWriter.Close()
+	}()
+	hash := git.MustIDFromString(sha)
+
+	return git.NewCommand("cat-file", "commit", sha).
+		RunInDirTimeoutEnvFullPipelineFunc(env, -1, repo.Path,
+			stdoutWriter, nil, nil,
+			func(ctx context.Context, cancel context.CancelFunc) error {
+				_ = stdoutWriter.Close()
+				commit, err := git.CommitFromReader(repo, hash, stdoutReader)
+				if err != nil {
+					return err
+				}
+				verification := models.ParseCommitWithSignature(commit)
+				if !verification.Verified {
+					cancel()
+					return &errUnverifiedCommit{
+						commit.ID.String(),
+					}
+				}
+				return nil
+			})
+}
+
+type errUnverifiedCommit struct {
+	sha string
+}
+
+func (e *errUnverifiedCommit) Error() string {
+	return fmt.Sprintf("Unverified commit: %s", e.sha)
+}
+
+func isErrUnverifiedCommit(err error) bool {
+	_, ok := err.(*errUnverifiedCommit)
+	return ok
+}