[PATCH] drm/i915/switcheroo: check for NULL before dereferencing

[Jani Nikula]

On Mon, 18 Aug 2025, Gustavo Sousa <gustavo.sousa at intel.com> wrote:
> Quoting Jani Nikula (2025-08-18 04:16:05-03:00)
>>Both i915_switcheroo_set_state() and i915_switcheroo_can_switch() check
>>for i915 == NULL. Commit d2e184f8e16a ("drm/i915/switcheroo: pass
>>display to HAS_DISPLAY()") started dereferencing it before the NULL
>>check. Fix it.
>
> Hm... Did it? I think i915->display will only give you an invalid
> address when i915 is NULL, but I don't think any dereferencing will
> happen, because of the checks on i915.

What would be the case for &i915->display, but not i915->display?

>
> Anyways, playing it safe here is probably a good idea. I would just
> reword the commit message a bit. With that,
>
> Reviewed-by: Gustavo Sousa <gustavo.sousa at intel.com>

Thanks.

>
>>
>>Fixes: d2e184f8e16a ("drm/i915/switcheroo: pass display to HAS_DISPLAY()")
>>Reported-by: kernel test robot <lkp at intel.com>
>>Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
>>Closes: https://lore.kernel.org/r/202508160035.hmzuKiww-lkp@intel.com/
>>Cc: Gustavo Sousa <gustavo.sousa at intel.com>
>>Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>>---
>> drivers/gpu/drm/i915/i915_switcheroo.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>>diff --git a/drivers/gpu/drm/i915/i915_switcheroo.c b/drivers/gpu/drm/i915/i915_switcheroo.c
>>index 231d27497706..3a95a55b2e87 100644
>>--- a/drivers/gpu/drm/i915/i915_switcheroo.c
>>+++ b/drivers/gpu/drm/i915/i915_switcheroo.c
>>@@ -15,7 +15,7 @@ static void i915_switcheroo_set_state(struct pci_dev *pdev,
>>                                       enum vga_switcheroo_state state)
>> {
>>         struct drm_i915_private *i915 = pdev_to_i915(pdev);
>>-        struct intel_display *display = i915->display;
>>+        struct intel_display *display = i915 ? i915->display : NULL;
>>         pm_message_t pmm = { .event = PM_EVENT_SUSPEND };
>> 
>>         if (!i915) {
>>@@ -45,7 +45,7 @@ static void i915_switcheroo_set_state(struct pci_dev *pdev,
>> static bool i915_switcheroo_can_switch(struct pci_dev *pdev)
>> {
>>         struct drm_i915_private *i915 = pdev_to_i915(pdev);
>>-        struct intel_display *display = i915->display;
>>+        struct intel_display *display = i915 ? i915->display : NULL;
>> 
>>         /*
>>          * FIXME: open_count is protected by drm_global_mutex but that would lead to
>>-- 
>>2.47.2
>>

-- 
Jani Nikula, Intel