Add more recover() at goroutine start points

This is a double-edged sword though as blind panic recovery
can lead to consistency issues in program state.

In particular, halting imapsql update push due to panic can lead
to a deadlock in IMAP code.

Panic in MTA-STS cache maintenance routine can lead to degraded
security.

internal/msgpipeline/check_runner.go

@@ -20,6 +20,7 @@ package msgpipeline
 
 import (
 	"context"
+	"runtime/debug"
 	"sync"
 
 	"github.com/emersion/go-message/textproto"
@@ -177,6 +178,14 @@ func (cr *checkRunner) runAndMergeResults(states []module.CheckState, runner fun
 		state := state
 		data.wg.Add(1)
 		go func() {
+			defer func() {
+				data.wg.Done()
+				if err := recover(); err != nil {
+					stack := debug.Stack()
+					log.Printf("panic during check execution: %v\n%s", err, stack)
+				}
+			}()
+
 			subCheckRes := runner(state)
 
 			// We check the length because we don't want to take locks
@@ -213,7 +222,6 @@ func (cr *checkRunner) runAndMergeResults(states []module.CheckState, runner fun
 				cr.log.Error("no check action", subCheckRes.Reason)
 			}
 
-			data.wg.Done()
 		}()
 	}
 

internal/storage/imapsql/imapsql.go

@@ -33,6 +33,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime/debug"
 	"runtime/trace"
 	"strconv"
 	"strings"
@@ -387,6 +388,11 @@ func (store *Storage) EnableUpdatePipe(mode updatepipe.BackendMode) error {
 		defer func() {
 			store.updPushStop <- struct{}{}
 			close(wrapped)
+
+			if err := recover(); err != nil {
+				stack := debug.Stack()
+				log.Printf("panic during imapsql update push: %v\n%s", err, stack)
+			}
 		}()
 
 		for {

internal/target/remote/security.go

@@ -22,6 +22,7 @@ import (
 	"context"
 	"crypto/tls"
 	"os"
+	"runtime/debug"
 	"time"
 
 	"github.com/foxcpp/go-mtasts"
@@ -107,6 +108,15 @@ func (c *mtastsPolicy) StartUpdater() {
 }
 
 func (c *mtastsPolicy) updater() {
+	defer func() {
+		if err := recover(); err != nil {
+			stack := debug.Stack()
+			log.Printf("panic during MTA-STS update: %v\n%s", err, stack)
+			log.Printf("MTA-STS cache refresh disabled due to critical error")
+			c.updaterStop = nil
+		}
+	}()
+
 	// Always update cache on start-up since we may have been down for some
 	// time.
 	c.log.Debugln("updating MTA-STS cache...")
@@ -395,6 +405,13 @@ func (c *daneDelivery) PrepareConn(ctx context.Context, mx string) {
 	c.tlsaFut = future.New()
 
 	go func() {
+		defer func() {
+			if err := recover(); err != nil {
+				stack := debug.Stack()
+				log.Printf("panic during extended resolver lookup: %v\n%s", err, stack)
+			}
+		}()
+
 		ad, recs, err := c.c.extResolver.AuthLookupTLSA(ctx, "25", "tcp", mx)
 		if err != nil {
 			c.tlsaFut.Set([]dns.TLSA{}, err)