This is a note to let you know that I've just added the patch titled drm/vkms: Fix null-ptr-deref in vkms_release() to the 6.1-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-vkms-fix-null-ptr-deref-in-vkms_release.patch and it can be found in the queue-6.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit b378d0228c6550514cdf0c4bdd4c3cfea008e696 Author: Yuan Can <yuancan@xxxxxxxxxx> Date: Tue Nov 1 06:51:56 2022 +0000 drm/vkms: Fix null-ptr-deref in vkms_release() [ Upstream commit 2fe2a8f40c21161ffe7653cc234e7934db5b7cc5 ] 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> Reviewed-by: Melissa Wen <mwen@xxxxxxxxxx> Signed-off-by: Melissa Wen <melissa.srw@xxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20221101065156.41584-3-yuancan@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c index dfe983eaa07ff..f716c5796f5fc 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); } static void vkms_atomic_commit_tail(struct drm_atomic_state *old_state)