[PATCH 3/3] media: venus: don't de-reference NULL pointers at IRQ time

[Mauro Carvalho Chehab]

Smatch is warning that:
        drivers/media/platform/qcom/venus/hfi_venus.c:1100 venus_isr() warn: 
variable dereferenced before check 'hdev' (see line 1097)

The logic basically does:
        hdev = to_hfi_priv(core);

with is translated to:
        hdev = core->priv;

If the IRQ code can receive a NULL pointer for hdev, there's
a bug there, as it will first try to de-reference the pointer,
and then check if it is null.

After looking at the code, it seems that this indeed can happen:
Basically, the venus IRQ thread is started with:
        devm_request_threaded_irq()
So, it will only be freed after the driver unbinds.

In order to prevent the IRQ code to work with freed data,
the logic at venus_hfi_destroy() sets core->priv to NULL,
which would make the IRQ code to ignore any pending IRQs.

There is, however a race condition, as core->priv is set
to NULL only after being freed. So, we need also to move the
core->priv = NULL to happen earlier.

Signed-off-by: Mauro Carvalho Chehab <mchehab+hua...@kernel.org>
---
 drivers/media/platform/qcom/venus/hfi_venus.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/qcom/venus/hfi_venus.c 
b/drivers/media/platform/qcom/venus/hfi_venus.c
index cebb20cf371f..ce98c523b3c6 100644
--- a/drivers/media/platform/qcom/venus/hfi_venus.c
+++ b/drivers/media/platform/qcom/venus/hfi_venus.c
@@ -1094,12 +1094,15 @@ static irqreturn_t venus_isr(struct venus_core *core)
 {
        struct venus_hfi_device *hdev = to_hfi_priv(core);
        u32 status;
-       void __iomem *cpu_cs_base = hdev->core->cpu_cs_base;
-       void __iomem *wrapper_base = hdev->core->wrapper_base;
+       void __iomem *cpu_cs_base;
+       void __iomem *wrapper_base;
 
        if (!hdev)
                return IRQ_NONE;
 
+       cpu_cs_base = hdev->core->cpu_cs_base;
+       wrapper_base = hdev->core->wrapper_base;
+
        status = readl(wrapper_base + WRAPPER_INTR_STATUS);
        if (IS_V6(core)) {
                if (status & WRAPPER_INTR_STATUS_A2H_MASK ||
@@ -1650,10 +1653,10 @@ void venus_hfi_destroy(struct venus_core *core)
 {
        struct venus_hfi_device *hdev = to_hfi_priv(core);
 
+       core->priv = NULL;
        venus_interface_queues_release(hdev);
        mutex_destroy(&hdev->lock);
        kfree(hdev);
-       core->priv = NULL;
        core->ops = NULL;
 }
 
-- 
2.30.2