[PATCH] strparser: Use worker disable API instead of cancellation in strp_done()

[Hyunwoo Kim <imv4bel@gmail.com>]

When strp_stop() and strp_done() are called without holding lock_sock(), 
they can race with worker-scheduling paths such as the Delayed ACK handler 
and ksoftirqd.
Specifically, after cancel_delayed_work_sync() and cancel_work_sync() are 
invoked from strp_done(), the workers may still be scheduled.
As a result, the workers may dereference freed objects.

To prevent these races, the cancellation APIs are replaced with 
worker-disabling APIs.

Fixes: 829385f08ae9 ("strparser: Use delayed work instead of timer for msg timeout")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 net/strparser/strparser.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c
index fe0e76fdd1f1..15cd9cadbd1a 100644
--- a/net/strparser/strparser.c
+++ b/net/strparser/strparser.c
@@ -503,8 +503,8 @@ void strp_done(struct strparser *strp)
 {
 	WARN_ON(!strp->stopped);
 
-	cancel_delayed_work_sync(&strp->msg_timer_work);
-	cancel_work_sync(&strp->work);
+	disable_delayed_work_sync(&strp->msg_timer_work);
+	disable_work_sync(&strp->work);
 
 	if (strp->skb_head) {
 		kfree_skb(strp->skb_head);
-- 
2.43.0

---
Dear,

The following is a simplified scenario illustrating how each race can occur. Since espintcp_close() does not hold lock_sock(), the race is possible.
Although cancel_work_sync(&strp->work) does not appear to be easy to trigger in practice here, it still seems better to fix it as well.
```
                 cpu0                                cpu1

espintcp_close()
                                         espintcp_data_ready()
                                           if (unlikely(strp->stopped)) return;
  strp_stop()
    strp->stopped = 1;
  strp_done()
    cancel_delayed_work_sync(&strp->msg_timer_work);
                                           strp_data_ready()
                                             strp_read_sock()
                                               tcp_read_sock()
                                                 __tcp_read_sock()
                                                   strp_recv()
                                                     __strp_recv()
                                                       strp_start_timer()
                                                         mod_delayed_work(strp_wq, &strp->msg_timer_work, timeo);  
```
```
                 cpu0                                cpu1

espintcp_close()
                                          sk->sk_data_ready()
                                            espintcp_data_ready()
                                              if (unlikely(strp->stopped)) return;
  strp_stop()
    strp->stopped = 1;
  strp_done()
    cancel_work_sync(&strp->work);
                                              if (strp_read_sock(strp) == -ENOMEM)
                                              queue_work()
```

Best regards,
Hyunwoo Kim