fix: bound CODEOWNERS regex match time (#38011)

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: wxiaoguang <wxiaoguang@gmail.com>

models/issues/pull.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"time"
 
 	"gitea.dev/models/db"
 	git_model "gitea.dev/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, "@")

models/issues/pull_test.go

@@ -4,7 +4,9 @@
 package issues_test
 
 import (
+	"strings"
 	"testing"
+	"time"
 
 	"gitea.dev/models/db"
 	issues_model "gitea.dev/models/issues"
@@ -39,6 +41,7 @@ func TestPullRequest(t *testing.T) {
 	t.Run("DeleteOrphanedObjects", testDeleteOrphanedObjects)
 	t.Run("ParseCodeOwnersLine", testParseCodeOwnersLine)
 	t.Run("CodeOwnerAbsolutePathPatterns", testCodeOwnerAbsolutePathPatterns)
+	t.Run("CodeOwnerPatternMatchTimeout", testCodeOwnerPatternMatchTimeout)
 	t.Run("GetApprovers", testGetApprovers)
 	t.Run("GetPullRequestByMergedCommit", testGetPullRequestByMergedCommit)
 	t.Run("Migrate_InsertPullRequests", testMigrateInsertPullRequests)
@@ -376,6 +379,22 @@ func testCodeOwnerAbsolutePathPatterns(t *testing.T) {
 	}
 }
 
+// testCodeOwnerPatternMatchTimeout ensures user-supplied CODEOWNERS patterns
+// cannot stall pull request processing through catastrophic regex backtracking:
+// each compiled rule must enforce a bounded match time.
+func testCodeOwnerPatternMatchTimeout(t *testing.T) {
+	rules, _ := issues_model.GetCodeOwnersFromContent(t.Context(), "(a+)+ @user5\n")
+	require.Len(t, rules, 1)
+
+	maliciousInput := strings.Repeat("a", 30) + "X"
+	start := time.Now()
+	_, err := rules[0].Rule.MatchString(maliciousInput)
+	elapsed := time.Since(start)
+
+	require.Error(t, err, "expected MatchTimeout error on pathological input")
+	assert.Less(t, elapsed, time.Second, "match timeout did not bound regex evaluation; took %s", elapsed)
+}
+
 func testGetApprovers(t *testing.T) {
 	pr := unittest.AssertExistsAndLoadBean(t, &issues_model.PullRequest{ID: 5})
 	// Official reviews are already deduplicated. Allow unofficial reviews