[PATCH V2 2/9] staging: vchiq_arm: Clear VLA warning

[Stefan Wahren]

The kernel would like to have all stack VLA usage removed[1]. The array
here is fixed (declared with a const variable) but it appears like a VLA
to the compiler. Also, currently we are putting 768 bytes on the
stack. This function is only called on the error path so performance is
not critical, let's just allocate the memory instead of using the
stack. This saves stack space and removes the VLA build warning.

kmalloc a buffer for dumping state instead of using the stack.

[1]: https://lkml.org/lkml/2018/3/7/621

CC: Kees Cook <keescook at google.com>
Signed-off-by: Tobin C. Harding <me at tobin.cc>
Signed-off-by: Stefan Wahren <stefan.wahren at i2se.com>
---
 .../vc04_services/interface/vchiq_arm/vchiq_arm.c  | 25 ++++++++++++++--------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
index 8575bd8..d46a5b8 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
@@ -3415,13 +3415,18 @@ vchiq_release_service(VCHIQ_SERVICE_HANDLE_T handle)
 	return ret;
 }
 
+struct service_data_struct {
+	int fourcc;
+	int clientid;
+	int use_count;
+};
+
 void
 vchiq_dump_service_use_state(VCHIQ_STATE_T *state)
 {
 	VCHIQ_ARM_STATE_T *arm_state = vchiq_platform_get_arm_state(state);
+	struct service_data_struct *service_data;
 	int i, j = 0;
-	/* Only dump 64 services */
-	static const int local_max_services = 64;
 	/* If there's more than 64 services, only dump ones with
 	 * non-zero counts */
 	int only_nonzero = 0;
@@ -3432,25 +3437,25 @@ vchiq_dump_service_use_state(VCHIQ_STATE_T *state)
 	int peer_count;
 	int vc_use_count;
 	int active_services;
-	struct service_data_struct {
-		int fourcc;
-		int clientid;
-		int use_count;
-	} service_data[local_max_services];
 
 	if (!arm_state)
 		return;
 
+	service_data = kmalloc_array(MAX_SERVICES, sizeof(*service_data),
+				     GFP_KERNEL);
+	if (!service_data)
+		return;
+
 	read_lock_bh(&arm_state->susp_res_lock);
 	vc_suspend_state = arm_state->vc_suspend_state;
 	vc_resume_state  = arm_state->vc_resume_state;
 	peer_count = arm_state->peer_use_count;
 	vc_use_count = arm_state->videocore_use_count;
 	active_services = state->unused_service;
-	if (active_services > local_max_services)
+	if (active_services > MAX_SERVICES)
 		only_nonzero = 1;
 
-	for (i = 0; (i < active_services) && (j < local_max_services); i++) {
+	for (i = 0; (i < active_services) && (j < MAX_SERVICES); i++) {
 		VCHIQ_SERVICE_T *service_ptr = state->services[i];
 
 		if (!service_ptr)
@@ -3494,6 +3499,8 @@ vchiq_dump_service_use_state(VCHIQ_STATE_T *state)
 	vchiq_log_warning(vchiq_susp_log_level,
 		"--- Overall vchiq instance use count %d", vc_use_count);
 
+	kfree(service_data);
+
 	vchiq_dump_platform_use_state(state);
 }
 
-- 
2.7.4