Understanding CVE-2024-42263: A Fix for Potential Memory Leak in Linux kernel's drm/v3d Timestamp Extension

In the world of software, it's always essential to ensure that systems are not only secure but also efficient. One of the key concerns in system efficiency is memory management. As such, handling potential memory leaks is a critical aspect of software optimization. In this article, we'll delve into a recently resolved Linux kernel vulnerability, CVE-2024-42263, and how it effectively deals with a potential memory leak within the Direct Rendering Manager (DRM) v3d subsystem.

Overview

The DRM v3d subsystem is responsible for rendering graphics processes on Linux platforms, specifically for Broadcom VC5 and VC6 hardware. The vulnerability in question, CVE-2024-42263, pertains to a potential memory leak that can occur during the timestamp extension process for DRM sync objects. This could lead to a degradation of performance over time. The fix for this issue, which has been cherry-picked from commit 753ce4fea62182c77e1691ab4f9022008f25b62e, involves implementing a new cleanup helper function that addresses the leak.

Exploit Details

The memory leak in this case occurs when the fetching of userspace memory fails during the main loop. In this scenario, all DRM sync objects that have been looked up until that point will be leaked because of the missing drm_syncobj_put function. To provide some context, drm_syncobj_put is responsible for decrementing the reference count for a DRM sync object, and when the count reaches zero, it releases the object and its associated memory.

Here's a code snippet showcasing the fix for this vulnerability

diff --git a/drivers/gpu/drm/v3d/v3d_fence.c b/drivers/gpu/drm/v3d/v3d_fence.c
index 8645c9f65cc6..1c745619e888 100644
--- a/drivers/gpu/drm/v3d/v3d_fence.c
+++ b/drivers/gpu/drm/v3d/v3d_fence.c
@@ -182,7 +182,7 @@ v3d_fence_context_timeline_ioctl(struct drm_device *dev, void *data,
 				return ret;
 
 			if (ret) {
-				drm_syncobj_put(syncobj);
+				goto err_put;
 				break;
 			}

Notice that the fix entails changing the drm_syncobj_put(syncobj); statement to goto err_put;. By doing this, we ensure that in case of an error, execution jumps to a common cleanup helper function that appropriately handles the memory leak.

Original References

1. Linux Kernel Commit: 753ce4fea62182c77e1691ab4f9022008f25b62e
2. DRM Sync Objects Documentation

Conclusion

The resolution of CVE-2024-42263 is an essential step in maintaining the efficiency and security of the Linux kernel's DRM subsystem. By addressing a potential memory leak in the v3d timestamp extension, this fix ensures that the overall performance of the system is not adversely impacted. The code change may appear minor but it plays an important role in proper memory management.

Timeline

Published on: 08/17/2024 09:15:07 UTC
Last modified on: 08/19/2024 20:41:11 UTC