nvme: Don't use a stack buffer for keep-alive command

In nvme_keep_alive() we pass a request with a pointer to an NVMe command on
the stack into blk_execute_rq_nowait().  However, the block layer doesn't
guarantee that the request is fully queued before blk_execute_rq_nowait()
returns.  If not, and the request is queued after nvme_keep_alive() returns,
then we'll end up using stack memory that might have been overwritten to
form the NVMe command we pass to hardware.

Fix this by keeping a special command struct in the nvme_ctrl struct right
next to the delayed work struct used for keep-alives.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

2 files changed, 4 insertions, 5 deletions

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 2fd8688cfa47..6d0490b477c9 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -796,13 +796,9 @@ static void nvme_keep_alive_end_io(struct request *rq, blk_status_t status)
 
 static int nvme_keep_alive(struct nvme_ctrl *ctrl)
 {
-        struct nvme_command c;
         struct request *rq;
 
-        memset(&c, 0, sizeof(c));
-        c.common.opcode = nvme_admin_keep_alive;
-
-        rq = nvme_alloc_request(ctrl->admin_q, &c, BLK_MQ_REQ_RESERVED,
+        rq = nvme_alloc_request(ctrl->admin_q, &ctrl->ka_cmd, BLK_MQ_REQ_RESERVED,
                         NVME_QID_ANY);
         if (IS_ERR(rq))
                 return PTR_ERR(rq);
@@ -834,6 +830,8 @@ void nvme_start_keep_alive(struct nvme_ctrl *ctrl)
                 return;
 
         INIT_DELAYED_WORK(&ctrl->ka_work, nvme_keep_alive_work);
+        memset(&ctrl->ka_cmd, 0, sizeof(ctrl->ka_cmd));
+        ctrl->ka_cmd.common.opcode = nvme_admin_keep_alive;
         schedule_delayed_work(&ctrl->ka_work, ctrl->kato * HZ);
 }
 EXPORT_SYMBOL_GPL(nvme_start_keep_alive);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 27e31c00b306..0521e4707d1c 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -183,6 +183,7 @@ struct nvme_ctrl {
         struct work_struct scan_work;
         struct work_struct async_event_work;
         struct delayed_work ka_work;
+        struct nvme_command ka_cmd;
         struct work_struct fw_act_work;
 
         /* Power saving configuration */