Before v4.15 commit 75492a51568b ("s390/scsi: Convert timers to use timer_setup()"), we intentionally only passed zfcp_adapter as context argument to zfcp_fsf_request_timeout_handler(). Since we only trigger adapter recovery, it was unnecessary to sync against races between timeout and (late) completion. Likewise, we only passed zfcp_erp_action as context argument to zfcp_erp_timeout_handler(). Since we only wakeup an ERP action, it was unnecessary to sync against races between timeout and (late) completion.

Meanwhile the timeout handlers get timer_list as context argument and do a timer-specific container-of to zfcp_fsf_req which can have been freed.

Fix it by making sure that any request timeout handlers, that might just have started before del_timer(), are completed by using del_timer_sync() instead. This ensures the request free happens afterwards.

Space time diagram of potential use-after-free:

Basic idea is to have 2 or more pending requests whose timeouts run out at almost the same time.

req 1 timeout ERP thread req 2 timeout ---------------- ---------------- --------------------------------------- zfcp_fsf_request_timeout_handler fsf_req = from_timer(fsf_req, t, timer) adapter = fsf_req->adapter zfcp_qdio_siosl(adapter) zfcp_erp_adapter_reopen(adapter,...) zfcp_erp_strategy ... zfcp_fsf_req_dismiss_all list_for_each_entry_safe zfcp_fsf_req_complete 1 del_timer 1 zfcp_fsf_req_free 1 zfcp_fsf_req_complete 2 zfcp_fsf_request_timeout_handler del_timer 2 fsf_req = from_timer(fsf_req, t, timer) zfcp_fsf_req_free 2 adapter = fsf_req->adapter ^^^^^^^ already freed

Suggested-by: Julian Wiedmann jwi@linux.ibm.com Reviewed-by: Julian Wiedmann jwi@linux.ibm.com Fixes: 75492a51568b ("s390/scsi: Convert timers to use timer_setup()") Cc: stable@vger.kernel.org #4.15+ Signed-off-by: Steffen Maier maier@linux.ibm.com --- drivers/s390/scsi/zfcp_fsf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/scsi/zfcp_fsf.c b/drivers/s390/scsi/zfcp_fsf.c index c795f22249d8..140186fe1d1e 100644 --- a/drivers/s390/scsi/zfcp_fsf.c +++ b/drivers/s390/scsi/zfcp_fsf.c @@ -434,7 +434,7 @@ static void zfcp_fsf_req_complete(struct zfcp_fsf_req *req) return; }

- del_timer(&req->timer); + del_timer_sync(&req->timer); zfcp_fsf_protstatus_eval(req); zfcp_fsf_fsfstatus_eval(req); req->handler(req); @@ -867,7 +867,7 @@ static int zfcp_fsf_req_send(struct zfcp_fsf_req *req) req->qdio_req.qdio_outb_usage = atomic_read(&qdio->req_q_free); req->issued = get_tod_clock(); if (zfcp_qdio_send(qdio, &req->qdio_req)) { - del_timer(&req->timer); + del_timer_sync(&req->timer); /* lookup request again, list might have changed */ zfcp_reqlist_find_rm(adapter->req_list, req_id); zfcp_erp_adapter_reopen(adapter, 0, "fsrs__1");