[PATCH 2/2] misc: fastrpc: fix init ordering race in rpmsg probe

[Vinayak Katoch]

fastrpc_device_register() calls misc_register() which makes the device
node visible to userspace. However, kref_init(), spin_lock_init(),
INIT_LIST_HEAD(), dev_set_drvdata() and fastrpc_cb_devices_create()
were all called after the switch/misc_register block, leaving a window
where userspace can open the device and call fastrpc_device_open() on
a partially initialised channel context.

On a concurrent open(), fastrpc_channel_ctx_get() calls kref_get() on
a kzalloc-zeroed, never kref_init()'d refcount of 0, triggering:

  refcount_t: addition on 0; use-after-free.
  Call trace:
   refcount_warn_saturate+0x120/0x148 (P)
   fastrpc_device_open+0x204/0x258 [fastrpc]
   misc_open+0xd8/0x1a0

Additionally, fastrpc_cb_devices_create() not having run means
sesscount is still 0, so fastrpc_session_alloc() returns NULL and
fastrpc_device_open() hits the error path which calls
fastrpc_channel_ctx_put() on the already-bogus refcount. This
triggers the free callback, kfree()-ing the channel context. A
subsequent IRQ-path fastrpc_rpmsg_callback() then dereferences the
freed spinlock:

  Unable to handle kernel paging request at virtual address ffffcd5841510ca0
  Internal error: Oops: 0000000096000047 [#1] SMP
  Call trace:
   queued_spin_lock_slowpath+0x414/0x5e0 (P)
   _raw_spin_lock_irqsave+0x74/0x90
   fastrpc_rpmsg_callback+0x4c/0xf0 [fastrpc]
   qcom_glink_native_rx+0x6c4/0xf10
   qcom_glink_smem_intr+0x1c/0x38 [qcom_glink_smem]
  Kernel panic - not syncing: Oops: Fatal exception in interrupt

Fix by moving all channel context initialisation (kref_init,
spin_lock_init, INIT_LIST_HEAD, idr_init, dev_set_drvdata) and
fastrpc_cb_devices_create() before fastrpc_device_register(), ensuring
the struct is fully ready before the device node is visible to
userspace.

Add err_depopulate label in the error path since
fastrpc_cb_devices_create() now runs before misc_register(); a
fastrpc_device_register() failure must call fastrpc_cb_devices_destroy()
to clean up the compute-cb children before freeing data.

Fixes: 3abe3ab3cdab ("misc: fastrpc: add secure domain support")
Signed-off-by: Vinayak Katoch <vinayak.katoch@xxxxxxxxxxxxxxxx>
---
 drivers/misc/fastrpc.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 7ab1cbbf19bb..93d07d28a0f1 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -2614,6 +2614,23 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	data->poll_mode_supported = soc_data->poll_mode_supported ||
 		of_machine_get_match(fastrpc_poll_supported_machines);
 
+	kref_init(&data->refcount);
+	atomic_set(&data->ctx_seq, 0);
+
+	rdev->dma_mask = &data->dma_mask;
+	dma_set_mask_and_coherent(rdev, DMA_BIT_MASK(32));
+	INIT_LIST_HEAD(&data->users);
+	INIT_LIST_HEAD(&data->invoke_interrupted_mmaps);
+	spin_lock_init(&data->lock);
+	idr_init(&data->ctx_idr);
+	data->domain_id = domain_id;
+	data->rpdev = rpdev;
+	dev_set_drvdata(&rpdev->dev, data);
+
+	err = fastrpc_cb_devices_create(rpdev);
+	if (err)
+		goto err_free_data;
+
 	switch (domain_id) {
 	case ADSP_DOMAIN_ID:
 	case MDSP_DOMAIN_ID:
@@ -2622,7 +2639,7 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 		data->unsigned_support = false;
 		err = fastrpc_device_register(rdev, data, secure_dsp, domain);
 		if (err)
-			goto err_free_data;
+			goto err_depopulate;
 		break;
 	case CDSP_DOMAIN_ID:
 	case GDSP_DOMAIN_ID:
@@ -2630,7 +2647,7 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 		/* Create both device nodes so that we can allow both Signed and Unsigned PD */
 		err = fastrpc_device_register(rdev, data, true, domain);
 		if (err)
-			goto err_free_data;
+			goto err_depopulate;
 
 		err = fastrpc_device_register(rdev, data, false, domain);
 		if (err)
@@ -2638,26 +2655,9 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 		break;
 	default:
 		err = -EINVAL;
-		goto err_free_data;
+		goto err_depopulate;
 	}
 
-	kref_init(&data->refcount);
-	atomic_set(&data->ctx_seq, 0);
-
-	rdev->dma_mask = &data->dma_mask;
-	dma_set_mask_and_coherent(rdev, DMA_BIT_MASK(32));
-	INIT_LIST_HEAD(&data->users);
-	INIT_LIST_HEAD(&data->invoke_interrupted_mmaps);
-	spin_lock_init(&data->lock);
-	idr_init(&data->ctx_idr);
-	data->domain_id = domain_id;
-	data->rpdev = rpdev;
-	dev_set_drvdata(&rpdev->dev, data);
-
-	err = fastrpc_cb_devices_create(rpdev);
-	if (err)
-		goto err_deregister_fdev;
-
 	if (data->domain_id == ADSP_DOMAIN_ID && data->sesscount > 0) {
 		struct fastrpc_session_ctx *last_sess;
 		struct fastrpc_session_ctx *dup_sess;
@@ -2682,6 +2682,9 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	if (data->secure_fdevice)
 		misc_deregister(&data->secure_fdevice->miscdev);
 
+err_depopulate:
+	fastrpc_cb_devices_destroy(rpdev);
+
 err_free_data:
 	kfree(data);
 	return err;

-- 
2.34.1