On 11/01, Yuan Can wrote:
> A null-ptr-deref is triggered when it tries to destroy the workqueue in
> vkms->output.composer_workq in vkms_release().
>
> KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
> CPU: 5 PID: 17193 Comm: modprobe Not tainted 6.0.0-11331-gd465bff130bf #24
> RIP: 0010:destroy_workqueue+0x2f/0x710
> ...
> Call Trace:
> <TASK>
> ? vkms_config_debugfs_init+0x50/0x50 [vkms]
> __devm_drm_dev_alloc+0x15a/0x1c0 [drm]
> vkms_init+0x245/0x1000 [vkms]
> do_one_initcall+0xd0/0x4f0
> do_init_module+0x1a4/0x680
> load_module+0x6249/0x7110
> __do_sys_finit_module+0x140/0x200
> do_syscall_64+0x35/0x80
> entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> The reason is that an OOM happened which triggers the destroy of the
> workqueue, however, the workqueue is alloced in the later process,
> thus a null-ptr-deref happened. A simple call graph is shown as below:
>
> vkms_init()
> vkms_create()
> devm_drm_dev_alloc()
> __devm_drm_dev_alloc()
> devm_drm_dev_init()
> devm_add_action_or_reset()
> devm_add_action() # an error happened
> devm_drm_dev_init_release()
> drm_dev_put()
> kref_put()
> drm_dev_release()
> vkms_release()
> destroy_workqueue() # null-ptr-deref happened
> vkms_modeset_init()
> vkms_output_init()
> vkms_crtc_init() # where the workqueue get allocated
>
> Fix this by checking if composer_workq is NULL before passing it to
> the destroy_workqueue() in vkms_release().
>
> Fixes: 6c234fe37c57 ("drm/vkms: Implement CRC debugfs API")
> Signed-off-by: Yuan Can <yuancan@xxxxxxxxxx>
> ---
> drivers/gpu/drm/vkms/vkms_drv.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index dfe983eaa07f..f716c5796f5f 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -57,7 +57,8 @@ static void vkms_release(struct drm_device *dev)
> {
> struct vkms_device *vkms = drm_device_to_vkms_device(dev);
>
> - destroy_workqueue(vkms->output.composer_workq);
> + if (vkms->output.composer_workq)
> + destroy_workqueue(vkms->output.composer_workq);
Reviewed-by: Melissa Wen <mwen@xxxxxxxxxx>
> }
>
> static void vkms_atomic_commit_tail(struct drm_atomic_state *old_state)
> --
> 2.17.1
>
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