-----原始邮件-----
发件人: "Hans Verkuil" [off-list ref]
发送时间: 2021-05-05 17:31:04 (星期三)
收件人: "Lv Yunlong" [off-list ref], s.nawrocki@samsung.com, mchehab@kernel.org, krzk@kernel.org
抄送: linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
主题: Re: [PATCH v3] media:exynos4-is: Fix a use after free in isp_video_release

Hi Lv Yunlong,

On 27/04/2021 15:27, Lv Yunlong wrote:

quoted

In isp_video_release, file->private_data is freed via
_vb2_fop_release()->v4l2_fh_release(). But the freed
file->private_data is still used in v4l2_fh_is_singular_file()
->v4l2_fh_is_singular(file->private_data), which is a use
after free bug.

My patch sets file->private_data to NULL after _vb2_fop_release()
to avoid the use after free, and uses a variable 'is_singular_file'
to keep the original function unchanged.

Actually, it is the use of 'is_singular_file' that fixes the bug,
the 'file->private_data = NULL;' is unnecessary here.

That said, it would be a really good idea if in a separate patch you
make v4l2_fh_release() more robust by setting filp->private_data to
NULL after the kfree(fh).

Regards,

	Hans

quoted

Fixes: 34947b8aebe3f ("[media] exynos4-is: Add the FIMC-IS ISP capture DMA driver")
Signed-off-by: Lv Yunlong <redacted>
---
 drivers/media/platform/exynos4-is/fimc-isp-video.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/exynos4-is/fimc-isp-video.c b/drivers/media/platform/exynos4-is/fimc-isp-video.c
index 612b9872afc8..c07dcb0bccc2 100644
--- a/drivers/media/platform/exynos4-is/fimc-isp-video.c
+++ b/drivers/media/platform/exynos4-is/fimc-isp-video.c

@@ -306,17 +306,21 @@ static int isp_video_release(struct file *file)
 	struct fimc_is_video *ivc = &isp->video_capture;
 	struct media_entity *entity = &ivc->ve.vdev.entity;
 	struct media_device *mdev = entity->graph_obj.mdev;
+	bool is_singular_file;
 
 	mutex_lock(&isp->video_lock);
 
-	if (v4l2_fh_is_singular_file(file) && ivc->streaming) {
+	is_singular_file = v4l2_fh_is_singular_file(file);
+
+	if (is_singular_file && ivc->streaming) {
 		media_pipeline_stop(entity);
 		ivc->streaming = 0;
 	}
 
 	_vb2_fop_release(file, NULL);
+	file->private_data = NULL;
 
-	if (v4l2_fh_is_singular_file(file)) {
+	if (is_singular_file) {
 		fimc_pipeline_call(&ivc->ve, close);
 
 		mutex_lock(&mdev->graph_mutex);

Ok, thanks for your suggestion.

Do you means i need submit a new path to set filp->private_data = NULL
after kfree(fh) in v4l2_fh_release() ?

Lv Yunlong
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