linux-kernel - [PATCH v4] media:exynos4-is: Fix a use after free in isp_video

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Date:   Sun,  9 May 2021 01:12:31 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     s.nawrocki@...sung.com, mchehab@...nel.org, krzk@...nel.org
Cc:     linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH v4] media:exynos4-is: Fix a use after free in isp_video_release

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 uses a variable 'is_singular_file' to avoid the uaf.
v3: https://lore.kernel.org/patchwork/patch/1419058/

Fixes: 34947b8aebe3f ("[media] exynos4-is: Add the FIMC-IS ISP capture DMA driver")
Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
---
 drivers/media/platform/exynos4-is/fimc-isp-video.c | 7 +++++--
 1 file changed, 5 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..3335fec509cb 100644
--- a/drivers/media/platform/exynos4-is/fimc-isp-video.c
+++ b/drivers/media/platform/exynos4-is/fimc-isp-video.c
@@ -306,17 +306,20 @@ 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);
 
-	if (v4l2_fh_is_singular_file(file)) {
+	if (is_singular_file) {
 		fimc_pipeline_call(&ivc->ve, close);
 
 		mutex_lock(&mdev->graph_mutex);
-- 
2.25.1