fix: bound CODEOWNERS regex match time (#38011) (#38025)

Backport #38011 by @bircni

User-supplied CODEOWNERS patterns were compiled without a match timeout,
so a crafted pattern (e.g. (a+)+) against a crafted file path could
backtrack for tens of seconds inside the PR creation transaction and
exhaust the database connection pool. Set MatchTimeout on each compiled
rule; the caller already treats match errors as non-matches.

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

models/issues/pull.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"time"
 
 	"code.gitea.io/gitea/models/db"
 	git_model "code.gitea.io/gitea/models/git"
@@ -860,6 +861,11 @@ func GetCodeOwnersFromContent(ctx context.Context, data string) ([]*CodeOwnerRul
 	return rules, warnings
 }
 
+// codeOwnerMatchTimeout bounds a single pattern match so a crafted pattern
+// cannot stall via catastrophic backtracking. See also the aggregate budget
+// enforced by the caller across the whole rules×files match loop.
+const codeOwnerMatchTimeout = 150 * time.Millisecond
+
 type CodeOwnerRule struct {
 	Rule     *regexp2.Regexp // it supports negative lookahead, does better for end users
 	Negative bool
@@ -888,6 +894,8 @@ func ParseCodeOwnersLine(ctx context.Context, tokens []string) (*CodeOwnerRule,
 		warnings = append(warnings, fmt.Sprintf("incorrect codeowner regexp: %s", err))
 		return nil, warnings
 	}
+	// Bound matching time so user-supplied patterns cannot stall PR creation via catastrophic backtracking.
+	rule.Rule.MatchTimeout = codeOwnerMatchTimeout
 
 	for _, user := range tokens[1:] {
 		user = strings.TrimPrefix(user, "@")