[PATCH 4.19.y] drm/vkms: call drm_atomic_helper_shutdown before drm_dev_put()

[guomengqi (A)]

在 2024/4/5 17:30, Greg KH 写道:
> On Wed, Apr 03, 2024 at 05:47:16PM +0800, Guo Mengqi wrote:
>> commit 73a82b22963d ("drm/atomic: Fix potential use-after-free
>> in nonblocking commits") introduced drm_dev_get/put() to
>> drm_atomic_helper_shutdown(). And this cause problem in vkms driver exit
>> process.
>>
>> vkms_exit()
>>    drm_dev_put()
>>      vkms_release()
>>        drm_atomic_helper_shutdown()
>>          drm_dev_get()
>>          drm_dev_put()
>>            vkms_release()    ------ null pointer access
>>
>> Using 4.19 stable x86 image on qemu, below stacktrace can be triggered by
>> load and unload vkms.ko.
>>
>> root:~ # insmod vkms.ko
>> [  142.135449] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
>> [  142.138713] [drm] Driver supports precise vblank timestamp query.
>> [  142.142390] [drm] Initialized vkms 1.0.0 20180514 for virtual device on minor 0
>> root:~ # rmmod vkms.ko
>> [  144.093710] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0
>> [  144.097491] PGD 800000023624e067 P4D 800000023624e067 PUD 22ab59067 PMD 0
>> [  144.100802] Oops: 0000 [#1] SMP PTI
>> [  144.102502] CPU: 0 PID: 3615 Comm: rmmod Not tainted 4.19.310 #1
>> [  144.104452] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
>> [  144.107238] RIP: 0010:device_del+0x34/0x3a0
>> ...
>> [  144.131323] Call Trace:
>> [  144.131962]  ? __die+0x7d/0xc0
>> [  144.132711]  ? no_context+0x152/0x3b0
>> [  144.133605]  ? wake_up_q+0x70/0x70
>> [  144.134436]  ? __do_page_fault+0x342/0x4b0
>> [  144.135445]  ? __switch_to_asm+0x41/0x70
>> [  144.136416]  ? __switch_to_asm+0x35/0x70
>> [  144.137366]  ? page_fault+0x1e/0x30
>> [  144.138214]  ? __drm_atomic_state_free+0x51/0x60
>> [  144.139331]  ? device_del+0x34/0x3a0
>> [  144.140197]  platform_device_del.part.14+0x19/0x70
>> [  144.141348]  platform_device_unregister+0xe/0x20
>> [  144.142458]  vkms_release+0x10/0x30 [vkms]
>> [  144.143449]  __drm_atomic_helper_disable_all.constprop.31+0x13b/0x150
>> [  144.144980]  drm_atomic_helper_shutdown+0x4b/0x90
>> [  144.146102]  vkms_release+0x18/0x30 [vkms]
>> [  144.147107]  vkms_exit+0x29/0x8ec [vkms]
>> [  144.148053]  __x64_sys_delete_module+0x155/0x220
>> [  144.149168]  do_syscall_64+0x43/0x100
>> [  144.150056]  entry_SYSCALL_64_after_hwframe+0x5c/0xc1
>>
>> It seems that the proper unload sequence is:
>> 	drm_atomic_helper_shutdown();
>> 	drm_dev_put();
>>
>> Just put drm_atomic_helper_shutdown() before drm_dev_put()
>> should solve the problem.
>>
>> Note that vkms exit code is refactored by 53d77aaa3f76 ("drm/vkms: Use
>> devm_drm_dev_alloc") in tags/v5.10-rc1.
>>
>> So this bug only exists on 4.19 and 5.4.
> Do we also need this for 5.4?  If so, can you send a version for that
> tree with the correct Fixes: information, and I will be glad to queue
> both of these up.

I sent a patch to 5.4.y too. Please check it at 
https://lore.kernel.org/all/20240409022647.1821-1-guomengqi3@huawei.com/T/#u

Thanks,

Mengqi

> thanks,
>
> greg k-h
> .