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Subject: Re: [PATCH] drm: fix double free for gbo in drm_gem_vram_init and
 drm_gem_vram_create
To:     <maarten.lankhorst@linux.intel.com>, <mripard@kernel.org>,
        <tzimmermann@suse.de>, <airlied@linux.ie>, <daniel@ffwll.ch>
References: <20200620062134.82961-1-jiayang5@huawei.com>
CC:     <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>
From:   Jia Yang <jiayang5@huawei.com>
Message-ID: <b6410a5e-2649-ba17-b4fe-eb24dab45253@huawei.com>
Date:   Wed, 1 Jul 2020 10:32:57 +0800
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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@huawei.com>
> Signed-off-by: Jia Yang <jiayang5@huawei.com>
> ---
>  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.
> + */
> +
>  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;
> +	}
>  	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;
>  
>  	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);
>  }
>  EXPORT_SYMBOL(drm_gem_vram_create);
>  
>