[PATCH v3] staging: vc04_services: Fix RCU dereference check

Padmanabha Srinivasaiah
2021-12-31T19:54:43Z

In service_callback path RCU dereferenced pointer struct vchiq_service
need to be accessed inside rcu read-critical section.

Also userdata/user_service part of vchiq_service is accessed around
different synchronization mechanism, getting an extra reference to a
pointer keeps sematics simpler and avoids prolonged graceperiod.

Accessing vchiq_service with rcu_read_[lock/unlock] fixes below issue.

[ 32.201659] =============================
[ 32.201664] WARNING: suspicious RCU usage
[ 32.201670] 5.15.11-rt24-v8+ #3 Not tainted
[ 32.201680] -----------------------------
[ 32.201685] drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h:529 suspicious rcu_dereference_check() usage!
[ 32.201695]
[ 32.201695] other info that might help us debug this:
[ 32.201695]
[ 32.201700]
[ 32.201700] rcu_scheduler_active = 2, debug_locks = 1
[ 32.201708] no locks held by vchiq-slot/0/98.
[ 32.201715]
[ 32.201715] stack backtrace:
[ 32.201723] CPU: 1 PID: 98 Comm: vchiq-slot/0 Not tainted 5.15.11-rt24-v8+ #3
[ 32.201733] Hardware name: Raspberry Pi 4 Model B Rev 1.4 (DT)
[ 32.201739] Call trace:
[ 32.201742] dump_backtrace+0x0/0x1b8
[ 32.201772] show_stack+0x20/0x30
[ 32.201784] dump_stack_lvl+0x8c/0xb8
[ 32.201799] dump_stack+0x18/0x34
[ 32.201808] lockdep_rcu_suspicious+0xe4/0xf8
[ 32.201817] service_callback+0x124/0x400
[ 32.201830] slot_handler_func+0xf60/0x1e20
[ 32.201839] kthread+0x19c/0x1a8
[ 32.201849] ret_from_fork+0x10/0x20

Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
---
Change in v3:
Taking an extra reference for service pointer to keep semantics
simpler to accesses in different synchronization mechanism.

Changes in v2:
RCU dereferenced pointer need to be accessed inside rcu
read-side critical section.

.../interface/vchiq_arm/vchiq_arm.c | 20 +++++++++++++++++--
1 file changed, 18 insertions(+), 2 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 6759a6261500..3a2e4582db8e 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
@@ -1058,15 +1058,27 @@ service_callback(enum vchiq_reason reason, struct vchiq_header *header,

DEBUG_TRACE(SERVICE_CALLBACK_LINE);

+ rcu_read_lock();
service = handle_to_service(handle);
- if (WARN_ON(!service))
+ if (WARN_ON(!service)) {
+ rcu_read_unlock();
return VCHIQ_SUCCESS;
+ }

user_service = (struct user_service *)service->base.userdata;
instance = user_service->instance;

- if (!instance || instance->closing)
+ if (!instance || instance->closing) {
+ rcu_read_unlock();
return VCHIQ_SUCCESS;
+ }
+
+ /*
+ * As hopping around different synchronization mechanism,
+ * taking an extra reference results in simpler implementation.
+ */
+ vchiq_service_get(service);
+ rcu_read_unlock();

vchiq_log_trace(vchiq_arm_log_level,
"%s - service %lx(%d,%p), reason %d, header %lx, instance %lx, bulk_userdata %lx",
@@ -1097,6 +1109,7 @@ service_callback(enum vchiq_reason reason, struct vchiq_header *header,
bulk_userdata);
if (status != VCHIQ_SUCCESS) {
DEBUG_TRACE(SERVICE_CALLBACK_LINE);
+ vchiq_service_put(service);
return status;
}
}
@@ -1105,10 +1118,12 @@ service_callback(enum vchiq_reason reason, struct vchiq_header *header,
if (wait_for_completion_interruptible(&user_service->remove_event)) {
vchiq_log_info(vchiq_arm_log_level, "%s interrupted", __func__);
DEBUG_TRACE(SERVICE_CALLBACK_LINE);
+ vchiq_service_put(service);
return VCHIQ_RETRY;
} else if (instance->closing) {
vchiq_log_info(vchiq_arm_log_level, "%s closing", __func__);
DEBUG_TRACE(SERVICE_CALLBACK_LINE);
+ vchiq_service_put(service);
return VCHIQ_ERROR;
}
DEBUG_TRACE(SERVICE_CALLBACK_LINE);
@@ -1137,6 +1152,7 @@ service_callback(enum vchiq_reason reason, struct vchiq_header *header,
header = NULL;
}
DEBUG_TRACE(SERVICE_CALLBACK_LINE);
+ vchiq_service_put(service);

if (skip_completion)
return VCHIQ_SUCCESS;
--
2.17.1