[PATCH] video/fbdev: Fix a double free in hvfb_probe

[PATCH] video/fbdev: 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 twice
by framebuffer_release(info).

My patch sets info->apertures to NULL after it was freed to avoid
double free.

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

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index c8b0ae676809..2fc9b507e73a 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -1032,6 +1032,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 		if (!pdev) {
 			pr_err("Unable to find PCI Hyper-V video\n");
 			kfree(info->apertures);
+			info->apertures = NULL;
 			return -ENODEV;
 		}
 
@@ -1130,6 +1131,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 		pci_dev_put(pdev);
 	}
 	kfree(info->apertures);
+	info->apertures = NULL;
 
 	return 0;
 
@@ -1142,6 +1144,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 	if (!gen2vm)
 		pci_dev_put(pdev);
 	kfree(info->apertures);
+	info->apertures = NULL;
 
 	return -ENOMEM;
 }
-- 
2.25.1


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Re: [PATCH] video/fbdev: Fix a double free in hvfb_probe

[Wei Liu]

Thanks for your patch.

I would like to change the prefix to "video: hyperv_fb:" to be more
specific.

On Tue, Mar 23, 2021 at 12:33:50AM -0700, Lv Yunlong wrote:
> 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 twice
> by framebuffer_release(info).
> 

I would say "freed for the second time" here. What you wrote reads to me
fraembuffer_release frees the buffer twice all by itself.

> My patch sets info->apertures to NULL after it was freed to avoid
> double free.
> 

I think this approach works. I would like to give other people a chance
to comment though.

Fixes: 3a6fb6c4255c ("video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.")

> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> ---
>  drivers/video/fbdev/hyperv_fb.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index c8b0ae676809..2fc9b507e73a 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -1032,6 +1032,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>  		if (!pdev) {
>  			pr_err("Unable to find PCI Hyper-V video\n");
>  			kfree(info->apertures);
> +			info->apertures = NULL;
>  			return -ENODEV;
>  		}
>  
> @@ -1130,6 +1131,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>  		pci_dev_put(pdev);
>  	}
>  	kfree(info->apertures);
> +	info->apertures = NULL;
>  
>  	return 0;
>  
> @@ -1142,6 +1144,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>  	if (!gen2vm)
>  		pci_dev_put(pdev);
>  	kfree(info->apertures);
> +	info->apertures = NULL;
>  
>  	return -ENOMEM;
>  }
> -- 
> 2.25.1
> 
> 
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RE: [PATCH] video/fbdev: Fix a double free in hvfb_probe

[Michael Kelley]

From: Lv Yunlong <lyl2019@mail.ustc.edu.cn> Sent: Tuesday, March 23, 2021 12:34 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 twice
> by framebuffer_release(info).
> 
> My patch sets info->apertures to NULL after it was freed to avoid
> double free.
> 
> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> ---
>  drivers/video/fbdev/hyperv_fb.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index c8b0ae676809..2fc9b507e73a 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -1032,6 +1032,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  		if (!pdev) {
>  			pr_err("Unable to find PCI Hyper-V video\n");
>  			kfree(info->apertures);
> +			info->apertures = NULL;
>  			return -ENODEV;
>  		}
> 
> @@ -1130,6 +1131,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  		pci_dev_put(pdev);
>  	}
>  	kfree(info->apertures);
> +	info->apertures = NULL;
> 
>  	return 0;
> 
> @@ -1142,6 +1144,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
>  	if (!gen2vm)
>  		pci_dev_put(pdev);
>  	kfree(info->apertures);
> +	info->apertures = NULL;
> 
>  	return -ENOMEM;
>  }
> --
> 2.25.1
> 

While I think this works, a slightly better solution might be to remove
all calls to kfree(info->apertures) in hvfb_getmem(),  and just let
framebuffer_release() handle freeing the memory.  That's what is
done in other drivers that follow the fbdev pattern, and it's less
code overall.  

Michael
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Re: RE: [PATCH] video/fbdev: Fix a double free in hvfb_probe

[lyl2019]

> -----原始邮件-----
> 发件人: "Michael Kelley" <mikelley@microsoft.com>
> 发送时间: 2021-03-24 02:52:07 (星期三)
> 收件人: "Lv Yunlong" <lyl2019@mail.ustc.edu.cn>, "KY Srinivasan" <kys@microsoft.com>, "Haiyang Zhang" <haiyangz@microsoft.com>, "Stephen Hemminger" <sthemmin@microsoft.com>, "wei.liu@kernel.org" <wei.liu@kernel.org>
> 抄送: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>, "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>, "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
> 主题: RE: [PATCH] video/fbdev: Fix a double free in hvfb_probe
> 
> From: Lv Yunlong <lyl2019@mail.ustc.edu.cn> Sent: Tuesday, March 23, 2021 12:34 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 twice
> > by framebuffer_release(info).
> > 
> > My patch sets info->apertures to NULL after it was freed to avoid
> > double free.
> > 
> > Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> > ---
> >  drivers/video/fbdev/hyperv_fb.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> > index c8b0ae676809..2fc9b507e73a 100644
> > --- a/drivers/video/fbdev/hyperv_fb.c
> > +++ b/drivers/video/fbdev/hyperv_fb.c
> > @@ -1032,6 +1032,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> > *info)
> >  		if (!pdev) {
> >  			pr_err("Unable to find PCI Hyper-V video\n");
> >  			kfree(info->apertures);
> > +			info->apertures = NULL;
> >  			return -ENODEV;
> >  		}
> > 
> > @@ -1130,6 +1131,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> > *info)
> >  		pci_dev_put(pdev);
> >  	}
> >  	kfree(info->apertures);
> > +	info->apertures = NULL;
> > 
> >  	return 0;
> > 
> > @@ -1142,6 +1144,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> > *info)
> >  	if (!gen2vm)
> >  		pci_dev_put(pdev);
> >  	kfree(info->apertures);
> > +	info->apertures = NULL;
> > 
> >  	return -ENOMEM;
> >  }
> > --
> > 2.25.1
> > 
> 
> While I think this works, a slightly better solution might be to remove
> all calls to kfree(info->apertures) in hvfb_getmem(),  and just let
> framebuffer_release() handle freeing the memory.  That's what is
> done in other drivers that follow the fbdev pattern, and it's less
> code overall.  
> 
> Michael

Ok, i agree with you. Remove all calls to kfree(info->apertures)
in hvfb_getmem() is a better solution.

I will subimt a PATCH v2 for you to review. Thanks.
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