Re: [PATCH] drm: fix double free for gbo in drm_gem_vram_init and drm_gem_vram_create

From: Jia Yang
Date: Wed Jul 01 2020 - 06:10:32 EST

Thanks for your suggestion, I can make the patch. But the
problem is reported by tool "Hulk Robot" and only happen
one time. No scripts are left, so I have no exact environment
to test.


On 2020/7/1 14:56, Thomas Zimmermann wrote:
> Hi
>
> Thanks for the patch and apologies for being late with the review.
>
> The fix is good, but I'd like to see different approach. I'd rather have
> drm_gem_vram_init() being integrated into drm_gem_vram_create().
>
> Do you prefer to make the patch or shall I type up something? Would you
> be able to test?
>
> I have some comments on the resulting changes below.
>
> Am 01.07.20 um 04:32 schrieb Jia Yang:
>> Ping...
>>
>> On 2020/6/20 14:21, Jia Yang wrote:
>>> I got a use-after-free report when doing some fuzz test:
>>>
>>> If ttm_bo_init() fails, the "gbo" and "gbo->bo.base" will be
>>> freed by ttm_buffer_object_destroy() in ttm_bo_init(). But
>>> then drm_gem_vram_create() and drm_gem_vram_init() will free
>>> "gbo" and "gbo->bo.base" again.
>>>
>>> BUG: KMSAN: use-after-free in drm_vma_offset_remove+0xb3/0x150
>>> CPU: 0 PID: 24282 Comm: syz-executor.1 Tainted: G B W 5.7.0-rc4-msan #2
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
>>> Call Trace:
>>> __dump_stack
>>> dump_stack+0x1c9/0x220
>>> kmsan_report+0xf7/0x1e0
>>> __msan_warning+0x58/0xa0
>>> drm_vma_offset_remove+0xb3/0x150
>>> drm_gem_free_mmap_offset
>>> drm_gem_object_release+0x159/0x180
>>> drm_gem_vram_init
>>> drm_gem_vram_create+0x7c5/0x990
>>> drm_gem_vram_fill_create_dumb
>>> drm_gem_vram_driver_dumb_create+0x238/0x590
>>> drm_mode_create_dumb
>>> drm_mode_create_dumb_ioctl+0x41d/0x450
>>> drm_ioctl_kernel+0x5a4/0x710
>>> drm_ioctl+0xc6f/0x1240
>>> vfs_ioctl
>>> ksys_ioctl
>>> __do_sys_ioctl
>>> __se_sys_ioctl+0x2e9/0x410
>>> __x64_sys_ioctl+0x4a/0x70
>>> do_syscall_64+0xb8/0x160
>>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>> RIP: 0033:0x4689b9
>>> Code: fd e0 fa ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb e0 fa ff c3 66 2e 0f 1f 84 00 00 00 00
>>> RSP: 002b:00007f368fa4dc98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>>> RAX: ffffffffffffffda RBX: 000000000076bf00 RCX: 00000000004689b9
>>> RDX: 0000000020000240 RSI: 00000000c02064b2 RDI: 0000000000000003
>>> RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>>> R13: 00000000004d17e0 R14: 00007f368fa4e6d4 R15: 000000000076bf0c
>>>
>>> Uninit was created at:
>>> kmsan_save_stack_with_flags
>>> kmsan_internal_poison_shadow+0x66/0xd0
>>> kmsan_slab_free+0x6e/0xb0
>>> slab_free_freelist_hook
>>> slab_free
>>> kfree+0x571/0x30a0
>>> drm_gem_vram_destroy
>>> ttm_buffer_object_destroy+0xc8/0x130
>>> ttm_bo_release
>>> kref_put
>>> ttm_bo_put+0x117d/0x23e0
>>> ttm_bo_init_reserved+0x11c0/0x11d0
>>> ttm_bo_init+0x289/0x3f0
>>> drm_gem_vram_init
>>> drm_gem_vram_create+0x775/0x990
>>> drm_gem_vram_fill_create_dumb
>>> drm_gem_vram_driver_dumb_create+0x238/0x590
>>> drm_mode_create_dumb
>>> drm_mode_create_dumb_ioctl+0x41d/0x450
>>> drm_ioctl_kernel+0x5a4/0x710
>>> drm_ioctl+0xc6f/0x1240
>>> vfs_ioctl
>>> ksys_ioctl
>>> __do_sys_ioctl
>>> __se_sys_ioctl+0x2e9/0x410
>>> __x64_sys_ioctl+0x4a/0x70
>>> do_syscall_64+0xb8/0x160
>>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>> If ttm_bo_init() fails, the "gbo" will be freed by
>>> ttm_buffer_object_destroy() in ttm_bo_init(). But then
>>> drm_gem_vram_create() and drm_gem_vram_init() will free
>>> "gbo" again.
>>>
>>> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
>>> Signed-off-by: Jia Yang <jiayang5@xxxxxxxxxx>
>>> ---
>>> drivers/gpu/drm/drm_gem_vram_helper.c | 28 +++++++++++++++------------
>>> 1 file changed, 16 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
>>> index 8b2d5c945c95..1d85af9a481a 100644
>>> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
>>> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
>>> @@ -175,6 +175,10 @@ static void drm_gem_vram_placement(struct drm_gem_vram_object *gbo,
>>> }
>>> }
>>>
>>> +/*
>>> + * Note that on error, drm_gem_vram_init will free the buffer object.
>>> + */
>>> +
>
> This comment could go away.
>
>>> static int drm_gem_vram_init(struct drm_device *dev,
>>> struct drm_gem_vram_object *gbo,
>>> size_t size, unsigned long pg_align)
>>> @@ -184,15 +188,19 @@ static int drm_gem_vram_init(struct drm_device *dev,
>>> int ret;
>>> size_t acc_size;
>>>
>>> - if (WARN_ONCE(!vmm, "VRAM MM not initialized"))
>>> + if (WARN_ONCE(!vmm, "VRAM MM not initialized")) {
>>> + kfree(gbo);
>>> return -EINVAL;
>>> + }
>
> This test can go to the top of drm_gem_vram_create()
>
>>> bdev = &vmm->bdev;
>>>
>>> gbo->bo.base.funcs = &drm_gem_vram_object_funcs;
>>>
>>> ret = drm_gem_object_init(dev, &gbo->bo.base, size);
>>> - if (ret)
>>> + if (ret) {
>>> + kfree(gbo);
>>> return ret;
>>> + }
>>>
>>> acc_size = ttm_bo_dma_acc_size(bdev, size, sizeof(*gbo));
>>>
>>> @@ -203,13 +211,13 @@ static int drm_gem_vram_init(struct drm_device *dev,
>>> &gbo->placement, pg_align, false, acc_size,
>>> NULL, NULL, ttm_buffer_object_destroy);
>>> if (ret)
>>> - goto err_drm_gem_object_release;
>>> + /*
>>> + * A failing ttm_bo_init will call ttm_buffer_object_destroy
>>> + * to release gbo->bo.base and kfree gbo.
>>> + */
>>> + return ret;
>
> The rest of this function would be inlined where the call to
> drm_gem_vram_init() currently happens.
>
>>>
>>> return 0;
>>> -
>>> -err_drm_gem_object_release:
>>> - drm_gem_object_release(&gbo->bo.base);
>>> - return ret;
>>> }
>>>
>>> /**
>>> @@ -243,13 +251,9 @@ struct drm_gem_vram_object *drm_gem_vram_create(struct drm_device *dev,
>>>
>>> ret = drm_gem_vram_init(dev, gbo, size, pg_align);
>>> if (ret < 0)
>>> - goto err_kfree;
>>> + return ERR_PTR(ret);
>>>
>>> return gbo;
>>> -
>>> -err_kfree:
>>> - kfree(gbo);
>>> - return ERR_PTR(ret);
>
> All inlined code up to ttm_bo_init() would jump to error labels on
> errors. ttm_bo_init() would return directly.
>
> Best regards
> Thomas
>
>
>>> }
>>> EXPORT_SYMBOL(drm_gem_vram_create);
>>>
>>>
>