[PATCH 6.6.y 3/3] drm/exynos: vidi: use ctx->lock to protect struct vidi_context member variables related to memory alloc/free

[Jeongjun Park <aha310510@gmail.com>]

[ Upstream commit 52b330799e2d6f825ae2bb74662ec1b10eb954bb ]

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 | 43 +++++++++++++++++++-----
 1 file changed, 35 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_vidi.c b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
index 576d79ebe9a8..b7eae2469b31 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_vidi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_vidi.c
@@ -186,15 +186,17 @@ 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 (!ctx->raw_edid)
 		ctx->raw_edid = (struct edid *)fake_edid_info;
@@ -202,14 +204,21 @@ static ssize_t vidi_store_connection(struct device *dev,
 	/* if raw_edid isn't same as fake data then it can't be tested. */
 	if (ctx->raw_edid != (struct edid *)fake_edid_info) {
 		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,
@@ -244,11 +253,14 @@ 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) {
 		struct edid *raw_edid;
@@ -271,20 +283,27 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data,
 					  "failed to allocate raw_edid.\n");
 			return -ENOMEM;
 		}
+		mutex_lock(&ctx->lock);
 		ctx->raw_edid = raw_edid;
+		mutex_unlock(&ctx->lock);
 	} else {
 		/*
 		 * with connection = 0, free raw_edid
 		 * only if raw edid data isn't same as fake data.
 		 */
+		mutex_lock(&ctx->lock);
 		if (ctx->raw_edid && ctx->raw_edid !=
 				(struct edid *)fake_edid_info) {
 			kfree(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;
@@ -299,7 +318,7 @@ 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;
 }
 
@@ -321,22 +340,24 @@ static int vidi_get_modes(struct drm_connector *connector)
 	struct vidi_context *ctx = ctx_from_connector(connector);
 	struct edid *edid;
 	int edid_len;
-	int count;
+	int count = 0;
 
 	/*
 	 * the edid data comes from user side and it would be set
 	 * to ctx->raw_edid through specific ioctl.
 	 */
+
+	mutex_lock(&ctx->lock);
 	if (!ctx->raw_edid) {
 		DRM_DEV_DEBUG_KMS(ctx->dev, "raw_edid is null.\n");
-		return 0;
+		goto fail;
 	}
 
 	edid_len = (1 + ctx->raw_edid->extensions) * EDID_LENGTH;
 	edid = kmemdup(ctx->raw_edid, edid_len, GFP_KERNEL);
 	if (!edid) {
 		DRM_DEV_DEBUG_KMS(ctx->dev, "failed to allocate edid\n");
-		return 0;
+		goto fail;
 	}
 
 	drm_connector_update_edid_property(connector, edid);
@@ -345,6 +366,8 @@ static int vidi_get_modes(struct drm_connector *connector)
 
 	kfree(edid);
 
+fail:
+	mutex_unlock(&ctx->lock);
 	return count;
 }
 
@@ -490,11 +513,15 @@ static int vidi_remove(struct platform_device *pdev)
 {
 	struct vidi_context *ctx = platform_get_drvdata(pdev);
 
+	mutex_lock(&ctx->lock);
+
 	if (ctx->raw_edid != (struct edid *)fake_edid_info) {
 		kfree(ctx->raw_edid);
 		ctx->raw_edid = NULL;
 	}
 
+	mutex_unlock(&ctx->lock);
+
 	component_del(&pdev->dev, &vidi_component_ops);
 
 	return 0;
--