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 <[email protected]>
---
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
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 <[email protected]>
> ---
> 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
>
>
From: Lv Yunlong <[email protected]> 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 <[email protected]>
> ---
> 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
> -----原始邮件-----
> 发件人: "Michael Kelley" <[email protected]>
> 发送时间: 2021-03-24 02:52:07 (星期三)
> 收件人: "Lv Yunlong" <[email protected]>, "KY Srinivasan" <[email protected]>, "Haiyang Zhang" <[email protected]>, "Stephen Hemminger" <[email protected]>, "[email protected]" <[email protected]>
> 抄送: "[email protected]" <[email protected]>, "[email protected]" <[email protected]>, "[email protected]" <[email protected]>, "[email protected]" <[email protected]>
> 主题: RE: [PATCH] video/fbdev: Fix a double free in hvfb_probe
>
> From: Lv Yunlong <[email protected]> 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 <[email protected]>
> > ---
> > 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.