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; }
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
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
-----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.
dri-devel@lists.freedesktop.org
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Lv Yunlong -
lyl2019＠mail.ustc.edu.cn
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Michael Kelley -
Wei Liu