CVE-2021-47490 in Linux
Summary
by MITRE • 05/22/2024
In the Linux kernel, the following vulnerability has been resolved:
drm/ttm: fix memleak in ttm_transfered_destroy
We need to cleanup the fences for ghost objects as well.
Bug: https://bugzilla.kernel.org/show_bug.cgi?id=214029 Bug: https://bugzilla.kernel.org/show_bug.cgi?id=214447
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Analysis
by VulDB Data Team • 01/07/2025
The vulnerability CVE-2021-47490 represents a memory leak issue within the Linux kernel's graphics subsystem, specifically affecting the Direct Rendering Manager (DRM) and the Transferable Memory Manager (TTM) component. This flaw exists in the ttm_transfered_destroy function where the kernel fails to properly clean up fence objects associated with ghost objects during memory management operations. The issue manifests when the kernel attempts to destroy transferred objects, leaving behind fence references that consume system memory without proper deallocation. Such memory leaks can accumulate over time, particularly in systems with intensive graphics workloads or frequent memory allocation/deallocation cycles, leading to gradual memory exhaustion and potential system instability.
The technical root cause of this vulnerability stems from incomplete resource cleanup within the TTM subsystem's object destruction mechanism. When ghost objects are transferred and subsequently destroyed, the kernel properly handles the primary object cleanup but neglects to release the associated fence synchronization primitives. This creates a memory leak pattern where fence objects remain allocated in kernel memory space, preventing the garbage collection mechanism from reclaiming the associated resources. The vulnerability aligns with CWE-401: Improper Release of Memory and represents a classic case of resource management failure in kernel space operations. The flaw specifically impacts the DRM subsystem's memory management pathways where TTM handles object transfers between different memory domains, creating a persistent memory consumption issue that grows with system usage.
The operational impact of CVE-2021-47490 extends beyond simple memory consumption, potentially affecting system stability and performance in graphics-intensive environments. Systems running graphics applications, virtualization platforms, or any workload that frequently utilizes DRM TTM memory management will experience gradual memory degradation, which could eventually lead to system slowdowns, application crashes, or even complete system hangs. The vulnerability is particularly concerning in server environments or embedded systems where long-running processes and continuous graphics operations are common. Attackers could potentially exploit this memory leak to cause denial of service conditions by forcing repeated memory allocation cycles that eventually exhaust available system memory, though the direct exploitation requires specific usage patterns that trigger the affected code path.
Mitigation strategies for this vulnerability primarily involve applying the official kernel patch that ensures proper fence cleanup during ghost object destruction. System administrators should prioritize updating to kernel versions containing the fix, typically kernel versions 5.14 and later, which include the necessary code modifications to address the memory leak. Additionally, monitoring system memory usage and implementing automated alerting for unusual memory consumption patterns can help detect potential exploitation attempts. The fix implemented addresses the specific code path in ttm_transfered_destroy by ensuring that fence objects are properly destroyed alongside ghost objects, preventing the accumulation of unreleased memory references. Organizations should also consider implementing memory monitoring tools that track kernel memory usage patterns to identify potential memory leak issues before they cause system instability, as this vulnerability operates at the kernel level where traditional user-space monitoring tools may not detect the problem effectively.