[PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

[PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

[Wang Hai]

p9_read_work and p9_fd_cancelled may be called concurrently.
In some cases, req->req_list may be deleted by both p9_read_work
and p9_fd_cancelled.

We can fix it by ignoring replies associated with a cancelled
request and ignoring cancelled request if message has been received
before lock.

Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
Reported-by: syzbot+77a25acfa0382e06ab23@syzkaller.appspotmail.com
Signed-off-by: Wang Hai <wanghai38@huawei.com>
---
v1->v2:
 1. Add ignoring replies associated with a cancelled request.
 2. Improved some descriptions suggested by Dominique.
 net/9p/trans_fd.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 13cd683a658a..3f67803123be 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -362,6 +362,10 @@ static void p9_read_work(struct work_struct *work)
 		if (m->rreq->status == REQ_STATUS_SENT) {
 			list_del(&m->rreq->req_list);
 			p9_client_cb(m->client, m->rreq, REQ_STATUS_RCVD);
+		} else if (m->rreq->status == REQ_STATUS_FLSHD) {
+			/* Ignore replies associated with a cancelled request. */
+			p9_debug(P9_DEBUG_TRANS,
+				 "Ignore replies associated with a cancelled request\n");
 		} else {
 			spin_unlock(&m->client->lock);
 			p9_debug(P9_DEBUG_ERROR,
@@ -703,11 +707,20 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
 {
 	p9_debug(P9_DEBUG_TRANS, "client %p req %p\n", client, req);
 
+	spin_lock(&client->lock);
+	/* Ignore cancelled request if message has been received
+	 * before lock.
+	 */
+	if (req->status == REQ_STATUS_RCVD) {
+		spin_unlock(&client->lock);
+		return 0;
+	}
+
 	/* we haven't received a response for oldreq,
 	 * remove it from the list.
 	 */
-	spin_lock(&client->lock);
 	list_del(&req->req_list);
+	req->status = REQ_STATUS_FLSHD;
 	spin_unlock(&client->lock);
 	p9_req_put(req);
 
-- 
2.17.1

Re: [PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

[Dominique Martinet]

Wang Hai wrote on Fri, Jun 12, 2020:
> p9_read_work and p9_fd_cancelled may be called concurrently.
> In some cases, req->req_list may be deleted by both p9_read_work
> and p9_fd_cancelled.
> 
> We can fix it by ignoring replies associated with a cancelled
> request and ignoring cancelled request if message has been received
> before lock.
> 
> Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
> Reported-by: syzbot+77a25acfa0382e06ab23@syzkaller.appspotmail.com
> Signed-off-by: Wang Hai <wanghai38@huawei.com>

Thanks! looks good to me, I'll queue for 5.9 as well unless you're in a
hurry.
-- 
Dominique

Re: [PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

[wanghai (M)]

在 2020/6/12 17:10, Dominique Martinet 写道:
> Wang Hai wrote on Fri, Jun 12, 2020:
>> p9_read_work and p9_fd_cancelled may be called concurrently.
>> In some cases, req->req_list may be deleted by both p9_read_work
>> and p9_fd_cancelled.
>>
>> We can fix it by ignoring replies associated with a cancelled
>> request and ignoring cancelled request if message has been received
>> before lock.
>>
>> Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
>> Reported-by: syzbot+77a25acfa0382e06ab23@syzkaller.appspotmail.com
>> Signed-off-by: Wang Hai <wanghai38@huawei.com>
> Thanks! looks good to me, I'll queue for 5.9 as well unless you're in a
> hurry.
Ok, thanks.