[PATCH v2] video: hyperv_fb: Fix a double free in hvfb_probe

[PATCH v2] video: hyperv_fb: Fix a double free in hvfb_probe

[Lv Yunlong]

In function hvfb_probe in hyperv_fb.c, it calls hvfb_getmem(hdev, info)
and return err when info->apertures is freed.

In the error1 label of hvfb_probe, info->apertures will be freed for the
second time in framebuffer_release(info).

My patch removes all kfree(info->apertures) instead of set info->apertures
to NULL. It is because that let framebuffer_release() handle freeing the
memory flows the fbdev pattern, and less code overall.

Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
---
 drivers/video/fbdev/hyperv_fb.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index c8b0ae676809..4dc9077dd2ac 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -1031,7 +1031,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 			PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
 		if (!pdev) {
 			pr_err("Unable to find PCI Hyper-V video\n");
-			kfree(info->apertures);
 			return -ENODEV;
 		}
 
@@ -1129,7 +1128,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 	} else {
 		pci_dev_put(pdev);
 	}
-	kfree(info->apertures);
 
 	return 0;
 
@@ -1141,7 +1139,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 err1:
 	if (!gen2vm)
 		pci_dev_put(pdev);
-	kfree(info->apertures);
 
 	return -ENOMEM;
 }
-- 
2.25.1

RE: [PATCH v2] video: hyperv_fb: Fix a double free in hvfb_probe

[Michael Kelley]

From: Lv Yunlong <lyl2019@mail.ustc.edu.cn> Sent: Wednesday, March 24, 2021 3:37 AM
> 
> In function hvfb_probe in hyperv_fb.c, it calls hvfb_getmem(hdev, info)
> and return err when info->apertures is freed.
> 
> In the error1 label of hvfb_probe, info->apertures will be freed for the
> second time in framebuffer_release(info).
> 
> My patch removes all kfree(info->apertures) instead of set info->apertures
> to NULL. It is because that let framebuffer_release() handle freeing the
> memory flows the fbdev pattern, and less code overall.

Let me suggest some clarifications in the commit message.  It's probably
better not to reference the initial approach of setting info->apertures to
NULL, since there won't be any record of that approach in the commit
history.  Here's what I would suggest:

Function hvfb_probe() calls hvfb_getmem(), expecting upon return that
info->apertures is either NULL or points to memory that should be freed
by framebuffer_release().  But hvfb_getmem() is freeing the memory and
leaving the pointer non-NULL, resulting in a double free if an error
occurs or later if hvfb_remove() is called.

Fix this by removing all kfree(info->apertures) calls in hvfb_getmem().
This will allow framebuffer_release() to free the memory, which follows
the pattern of other fbdev drivers.

Modulo this revision to the commit message, which Wei Liu can
probably incorporate,

Reviewed-by: Michael Kelley <mikelley@microsoft.com>

> 
> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> ---
>  drivers/video/fbdev/hyperv_fb.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index c8b0ae676809..4dc9077dd2ac 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -1031,7 +1031,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  			PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
>  		if (!pdev) {
>  			pr_err("Unable to find PCI Hyper-V video\n");
> -			kfree(info->apertures);
>  			return -ENODEV;
>  		}
> 
> @@ -1129,7 +1128,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  	} else {
>  		pci_dev_put(pdev);
>  	}
> -	kfree(info->apertures);
> 
>  	return 0;
> 
> @@ -1141,7 +1139,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  err1:
>  	if (!gen2vm)
>  		pci_dev_put(pdev);
> -	kfree(info->apertures);
> 
>  	return -ENOMEM;
>  }
> --
> 2.25.1
> 

Re: [PATCH v2] video: hyperv_fb: Fix a double free in hvfb_probe

[Wei Liu]

On Wed, Mar 24, 2021 at 01:46:39PM +0000, Michael Kelley wrote:
> From: Lv Yunlong <lyl2019@mail.ustc.edu.cn> Sent: Wednesday, March 24, 2021 3:37 AM
> > 
> > In function hvfb_probe in hyperv_fb.c, it calls hvfb_getmem(hdev, info)
> > and return err when info->apertures is freed.
> > 
> > In the error1 label of hvfb_probe, info->apertures will be freed for the
> > second time in framebuffer_release(info).
> > 
> > My patch removes all kfree(info->apertures) instead of set info->apertures
> > to NULL. It is because that let framebuffer_release() handle freeing the
> > memory flows the fbdev pattern, and less code overall.
> 
> Let me suggest some clarifications in the commit message.  It's probably
> better not to reference the initial approach of setting info->apertures to
> NULL, since there won't be any record of that approach in the commit
> history.  Here's what I would suggest:
> 
> Function hvfb_probe() calls hvfb_getmem(), expecting upon return that
> info->apertures is either NULL or points to memory that should be freed
> by framebuffer_release().  But hvfb_getmem() is freeing the memory and
> leaving the pointer non-NULL, resulting in a double free if an error
> occurs or later if hvfb_remove() is called.
> 
> Fix this by removing all kfree(info->apertures) calls in hvfb_getmem().
> This will allow framebuffer_release() to free the memory, which follows
> the pattern of other fbdev drivers.
> 
> Modulo this revision to the commit message, which Wei Liu can
> probably incorporate,
> 

Yes. I surely can incorporate the changes.

I will also add the Fixes tag.

> Reviewed-by: Michael Kelley <mikelley@microsoft.com>