[PATCH 0/3 RESEND] drm/exynos: vidi: fix various memory corruption bugs

[PATCH 0/3 RESEND] drm/exynos: vidi: fix various memory corruption bugs

[Jeongjun Park]

This is a series of patches that address several memory bugs that occur
in the Exynos Virtual Display driver.

Jeongjun Park (3):
  drm/exynos: vidi: use priv->vidi_dev for ctx lookup in vidi_connection_ioctl()
  drm/exynos: vidi: fix to avoid directly dereferencing user pointer
  drm/exynos: vidi: use ctx->lock to protect struct vidi_context member variables related to memory alloc/free

 drivers/gpu/drm/exynos/exynos_drm_drv.h  |  1 +
 drivers/gpu/drm/exynos/exynos_drm_vidi.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 64 insertions(+), 11 deletions(-)

[PATCH 1/3 RESEND] drm/exynos: vidi: use priv->vidi_dev for ctx lookup in vidi_connection_ioctl()

[Jeongjun Park]

vidi_connection_ioctl() retrieves the driver_data from drm_dev->dev to
obtain a struct vidi_context pointer. However, drm_dev->dev is the
exynos-drm master device, and the driver_data contained therein is not
the vidi component device, but a completely different device.

This can lead to various bugs, ranging from null pointer dereferences and
garbage value accesses to, in unlucky cases, out-of-bounds errors,
use-after-free errors, and more.

To resolve this issue, we need to store/delete the vidi device pointer in
exynos_drm_private->vidi_dev during bind/unbind, and then read this
exynos_drm_private->vidi_dev within ioctl() to obtain the correct
struct vidi_context pointer.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 drivers/gpu/drm/exynos/exynos_drm_drv.h  |  1 +
 drivers/gpu/drm/exynos/exynos_drm_vidi.c | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.h b/drivers/gpu/drm/exynos/exynos_drm_drv.h
index 23646e55f142..06c29ff2aac0 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_drv.h
+++ b/drivers/gpu/drm/exynos/exynos_drm_drv.h
@@ -199,6 +199,7 @@ struct drm_exynos_file_private {
 struct exynos_drm_private {
 	struct device *g2d_dev;
 	struct device *dma_dev;
+	struct device *vidi_dev;
 	void *mapping;
 
 	/* for atomic commit */
diff --git a/drivers/gpu/drm/exynos/exynos_drm_vidi.c b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
index e094b8bbc0f1..1fe297d512e7 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_vidi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
@@ -223,9 +223,14 @@ ATTRIBUTE_GROUPS(vidi);
 int vidi_connection_ioctl(struct drm_device *drm_dev, void *data,
 				struct drm_file *file_priv)
 {
-	struct vidi_context *ctx = dev_get_drvdata(drm_dev->dev);
+	struct exynos_drm_private *priv = drm_dev->dev_private;
+	struct device *dev = priv ? priv->vidi_dev : NULL;
+	struct vidi_context *ctx = dev ? dev_get_drvdata(dev) : NULL;
 	struct drm_exynos_vidi_connection *vidi = data;
 
+	if (!ctx)
+		return -ENODEV;
+
 	if (!vidi) {
 		DRM_DEV_DEBUG_KMS(ctx->dev,
 				  "user data for vidi is null.\n");
@@ -371,6 +376,7 @@ static int vidi_bind(struct device *dev, struct device *master, void *data)
 {
 	struct vidi_context *ctx = dev_get_drvdata(dev);
 	struct drm_device *drm_dev = data;
+	struct exynos_drm_private *priv = drm_dev->dev_private;
 	struct drm_encoder *encoder = &ctx->encoder;
 	struct exynos_drm_plane *exynos_plane;
 	struct exynos_drm_plane_config plane_config = { 0 };
@@ -378,6 +384,8 @@ static int vidi_bind(struct device *dev, struct device *master, void *data)
 	int ret;
 
 	ctx->drm_dev = drm_dev;
+	if (priv)
+		priv->vidi_dev = dev;
 
 	plane_config.pixel_formats = formats;
 	plane_config.num_pixel_formats = ARRAY_SIZE(formats);
@@ -423,8 +431,12 @@ static int vidi_bind(struct device *dev, struct device *master, void *data)
 static void vidi_unbind(struct device *dev, struct device *master, void *data)
 {
 	struct vidi_context *ctx = dev_get_drvdata(dev);
+	struct drm_device *drm_dev = data;
+	struct exynos_drm_private *priv = drm_dev->dev_private;
 
 	timer_delete_sync(&ctx->timer);
+	if (priv)
+		priv->vidi_dev = NULL;
 }
 
 static const struct component_ops vidi_component_ops = {
--

[PATCH 2/3 RESEND] drm/exynos: vidi: fix to avoid directly dereferencing user pointer

[Jeongjun Park]

In vidi_connection_ioctl(), vidi->edid(user pointer) is directly
dereferenced in the kernel.

This allows arbitrary kernel memory access from the user space, so instead
of directly accessing the user pointer in the kernel, we should modify it
to copy edid to kernel memory using copy_from_user() and use it.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 drivers/gpu/drm/exynos/exynos_drm_vidi.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_vidi.c b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
index 1fe297d512e7..601406b640c7 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_vidi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
@@ -251,13 +251,27 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data,
 
 	if (vidi->connection) {
 		const struct drm_edid *drm_edid;
-		const struct edid *raw_edid;
+		const void __user *edid_userptr = u64_to_user_ptr(vidi->edid);
+		void *edid_buf;
+		struct edid hdr;
 		size_t size;
 
-		raw_edid = (const struct edid *)(unsigned long)vidi->edid;
-		size = (raw_edid->extensions + 1) * EDID_LENGTH;
+		if (copy_from_user(&hdr, edid_userptr, sizeof(hdr)))
+			return -EFAULT;
 
-		drm_edid = drm_edid_alloc(raw_edid, size);
+		size = (hdr.extensions + 1) * EDID_LENGTH;
+
+		edid_buf = kmalloc(size, GFP_KERNEL);
+		if (!edid_buf)
+			return -ENOMEM;
+
+		if (copy_from_user(edid_buf, edid_userptr, size)) {
+			kfree(edid_buf);
+			return -EFAULT;
+		}
+
+		drm_edid = drm_edid_alloc(edid_buf, size);
+		kfree(edid_buf);
 		if (!drm_edid)
 			return -ENOMEM;
 
--

[PATCH 3/3 RESEND] drm/exynos: vidi: use ctx->lock to protect struct vidi_context member variables related to memory alloc/free

[Jeongjun Park]

Exynos Virtual Display driver performs memory alloc/free operations
without lock protection, which easily causes concurrency problem.

For example, use-after-free can occur in race scenario like this:
```
	CPU0				CPU1				CPU2
	----				----				----
  vidi_connection_ioctl()
    if (vidi->connection) // true
      drm_edid = drm_edid_alloc(); // alloc drm_edid
      ...
      ctx->raw_edid = drm_edid;
      ...
								drm_mode_getconnector()
								  drm_helper_probe_single_connector_modes()
								    vidi_get_modes()
								      if (ctx->raw_edid) // true
								        drm_edid_dup(ctx->raw_edid);
								          if (!drm_edid) // false
								          ...
				vidi_connection_ioctl()
				  if (vidi->connection) // false
				    drm_edid_free(ctx->raw_edid); // free drm_edid
				    ...
								          drm_edid_alloc(drm_edid->edid)
								            kmemdup(edid); // UAF!!
								            ...
```

To prevent these vulns, at least in vidi_context, member variables related
to memory alloc/free should be protected with ctx->lock.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 drivers/gpu/drm/exynos/exynos_drm_vidi.c | 38 ++++++++++++++++++++----
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_vidi.c b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
index 601406b640c7..37733f2ac0e7 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_vidi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
@@ -186,29 +186,37 @@ static ssize_t vidi_store_connection(struct device *dev,
 				const char *buf, size_t len)
 {
 	struct vidi_context *ctx = dev_get_drvdata(dev);
-	int ret;
+	int ret, new_connected;
 
-	ret = kstrtoint(buf, 0, &ctx->connected);
+	ret = kstrtoint(buf, 0, &new_connected);
 	if (ret)
 		return ret;
-
-	if (ctx->connected > 1)
+	if (new_connected > 1)
 		return -EINVAL;
 
+	mutex_lock(&ctx->lock);
+
 	/*
 	 * Use fake edid data for test. If raw_edid is set then it can't be
 	 * tested.
 	 */
 	if (ctx->raw_edid) {
 		DRM_DEV_DEBUG_KMS(dev, "edid data is not fake data.\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto fail;
 	}
 
+	ctx->connected = new_connected;
+	mutex_unlock(&ctx->lock);
+
 	DRM_DEV_DEBUG_KMS(dev, "requested connection.\n");
 
 	drm_helper_hpd_irq_event(ctx->drm_dev);
 
 	return len;
+fail:
+	mutex_unlock(&ctx->lock);
+	return ret;
 }
 
 static DEVICE_ATTR(connection, 0644, vidi_show_connection,
@@ -243,11 +251,14 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data,
 		return -EINVAL;
 	}
 
+	mutex_lock(&ctx->lock);
 	if (ctx->connected == vidi->connection) {
+		mutex_unlock(&ctx->lock);
 		DRM_DEV_DEBUG_KMS(ctx->dev,
 				  "same connection request.\n");
 		return -EINVAL;
 	}
+	mutex_unlock(&ctx->lock);
 
 	if (vidi->connection) {
 		const struct drm_edid *drm_edid;
@@ -281,14 +292,21 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data,
 					  "edid data is invalid.\n");
 			return -EINVAL;
 		}
+		mutex_lock(&ctx->lock);
 		ctx->raw_edid = drm_edid;
+		mutex_unlock(&ctx->lock);
 	} else {
 		/* with connection = 0, free raw_edid */
+		mutex_lock(&ctx->lock);
 		drm_edid_free(ctx->raw_edid);
 		ctx->raw_edid = NULL;
+		mutex_unlock(&ctx->lock);
 	}
 
+	mutex_lock(&ctx->lock);
 	ctx->connected = vidi->connection;
+	mutex_unlock(&ctx->lock);
+
 	drm_helper_hpd_irq_event(ctx->drm_dev);
 
 	return 0;
@@ -303,7 +321,7 @@ static enum drm_connector_status vidi_detect(struct drm_connector *connector,
 	 * connection request would come from user side
 	 * to do hotplug through specific ioctl.
 	 */
-	return ctx->connected ? connector_status_connected :
+	return READ_ONCE(ctx->connected) ? connector_status_connected :
 			connector_status_disconnected;
 }
 
@@ -326,11 +344,15 @@ static int vidi_get_modes(struct drm_connector *connector)
 	const struct drm_edid *drm_edid;
 	int count;
 
+	mutex_lock(&ctx->lock);
+
 	if (ctx->raw_edid)
 		drm_edid = drm_edid_dup(ctx->raw_edid);
 	else
 		drm_edid = drm_edid_alloc(fake_edid_info, sizeof(fake_edid_info));
 
+	mutex_unlock(&ctx->lock);
+
 	drm_edid_connector_update(connector, drm_edid);
 
 	count = drm_edid_connector_add_modes(connector);
@@ -482,9 +504,13 @@ static void vidi_remove(struct platform_device *pdev)
 {
 	struct vidi_context *ctx = platform_get_drvdata(pdev);
 
+	mutex_lock(&ctx->lock);
+
 	drm_edid_free(ctx->raw_edid);
 	ctx->raw_edid = NULL;
 
+	mutex_unlock(&ctx->lock);
+
 	component_del(&pdev->dev, &vidi_component_ops);
 }
 
--

Re: [PATCH 0/3 RESEND] drm/exynos: vidi: fix various memory corruption bugs

[Jeongjun Park]

Hello Inki,

Inki Dae <daeinki@gmail.com> wrote:
>
> Hello Mr Park,
>
> I'm sorry for being late. I forgot to review the patch you had posted before. I will proceed with the review soon.
>
> Thanks,
> Inki Dae
>

Sorry I checked my email again and realized I forgot to add the Fixes tag.
I'll write a v2 patch and send it to you right away.

Regards,
Jeongjun Park

>
> 2026년 1월 19일 (월) 오후 5:26, Jeongjun Park <aha310510@gmail.com>님이 작성:
>>
>> This is a series of patches that address several memory bugs that occur
>> in the Exynos Virtual Display driver.
>>
>> Jeongjun Park (3):
>>   drm/exynos: vidi: use priv->vidi_dev for ctx lookup in vidi_connection_ioctl()
>>   drm/exynos: vidi: fix to avoid directly dereferencing user pointer
>>   drm/exynos: vidi: use ctx->lock to protect struct vidi_context member variables related to memory alloc/free
>>
>>  drivers/gpu/drm/exynos/exynos_drm_drv.h  |  1 +
>>  drivers/gpu/drm/exynos/exynos_drm_vidi.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------
>>  2 files changed, 64 insertions(+), 11 deletions(-)
>>