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 @@ -377,6 +377,10 @@ 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, @@ -718,11 +722,20 @@ 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);
