[PATCH v2 14/14] firmware: arm_scmi: Publish mailbox cinfo before channel request

[Sudeep Holla <sudeep.holla@kernel.org>]

mailbox_chan_setup() initializes smbox->cinfo only after all mailbox
channels have been requested successfully. That is too late because
mbox_request_channel() binds the client before invoking the controller
startup callback, and startup can enable interrupt delivery.

If a pending or spurious mailbox interrupt fires during that window,
mbox_chan_received_data() can call the SCMI mailbox rx_callback() before
smbox->cinfo is set. The callback dereferences smbox->cinfo on both the
spurious IRQ path and the normal RX path, so this can crash before
channel setup has completed.

Publish cinfo->transport_info and smbox->cinfo, and initialize the
chan_lock, before requesting any mailbox channel. Clear the early
published pointers again on setup failure so later cleanup does not see
a half-initialized transport.

Fixes: 5c8a47a5a91d ("firmware: arm_scmi: Make scmi core independent of the transport type")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>
---
 drivers/firmware/arm_scmi/transports/mailbox.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/arm_scmi/transports/mailbox.c b/drivers/firmware/arm_scmi/transports/mailbox.c
index 07a08ea5d9de..f1bee48ef7dd 100644
--- a/drivers/firmware/arm_scmi/transports/mailbox.c
+++ b/drivers/firmware/arm_scmi/transports/mailbox.c
@@ -211,13 +211,18 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	cl->tx_block = false;
 	cl->knows_txdone = tx;
 
+	cinfo->transport_info = smbox;
+	smbox->cinfo = cinfo;
+	mutex_init(&smbox->chan_lock);
+
 	smbox->chan = mbox_request_channel(cl, tx ? 0 : p2a_chan);
 	if (IS_ERR(smbox->chan)) {
 		ret = PTR_ERR(smbox->chan);
+		smbox->chan = NULL;
 		if (ret != -EPROBE_DEFER)
 			dev_err(cdev,
 				"failed to request SCMI %s mailbox\n", desc);
-		return ret;
+		goto err_clear_cinfo;
 	}
 
 	/* Additional unidirectional channel for TX if needed */
@@ -243,16 +248,15 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 		}
 	}
 
-	cinfo->transport_info = smbox;
-	smbox->cinfo = cinfo;
-	mutex_init(&smbox->chan_lock);
-
 	return 0;
 
 err_free_chan_receiver:
 	mbox_free_channel(smbox->chan_receiver);
 err_free_chan:
 	mbox_free_channel(smbox->chan);
+err_clear_cinfo:
+	cinfo->transport_info = NULL;
+	smbox->cinfo = NULL;
 	return ret;
 }
 

-- 
2.43.0