The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 74d6a5d5662975aed7f25952f62efbb6f6dadd29 Mon Sep 17 00:00:00 2001

From: Wang Hai wanghai38@huawei.com Date: Fri, 12 Jun 2020 17:08:33 +0800 Subject: [PATCH] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

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@huawei.com Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function") Cc: stable@vger.kernel.org # v3.12+ Reported-by: syzbot+77a25acfa0382e06ab23@syzkaller.appspotmail.com Signed-off-by: Wang Hai wanghai38@huawei.com Signed-off-by: Dominique Martinet asmadeus@codewreck.org

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index 9c9196d30a59..12ecacf0c55f 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);