[PATCH 5.7 013/120] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

From: Greg Kroah-Hartman
Date: Mon Aug 03 2020 - 08:57:29 EST


From: Wang Hai <wanghai38@xxxxxxxxxx>

commit 74d6a5d5662975aed7f25952f62efbb6f6dadd29 upstream.

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.

Link: http://lkml.kernel.org/r/20200612090833.36149-1-wanghai38@xxxxxxxxxx
Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.12+
Reported-by: syzbot+77a25acfa0382e06ab23@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
Signed-off-by: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
net/9p/trans_fd.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -362,6 +362,10 @@ static void p9_read_work(struct work_str
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_cli
{
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);