CVE-2026-63863 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/gpusvm: Fix unbalanced unlock in drm_gpusvm_scan_mm()
There is a unbalanced lock/unlock to gpusvm notifier lock: [ 931.045868] =====================================
[ 931.046509] WARNING: bad unlock balance detected!
[ 931.047149] 6.19.0-rc6+xe-**************** #9 Tainted: G U
[ 931.048150] -------------------------------------
[ 931.048790] kworker/u5:0/51 is trying to release lock (&gpusvm->notifier_lock) at:
[ 931.049801] [] drm_gpusvm_scan_mm+0x188/0x460 [drm_gpusvm_helper]
[ 931.050802] but there are no more locks to release!
[ 931.051463]
The drm_gpusvm_notifier_unlock() sits under err_free label and the first jump to err_free is just before calling the drm_gpusvm_notifier_lock() causing unbalanced unlock.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the Linux kernel's graphics subsystem, specifically in the drm_gpusvm_helper module where improper lock management leads to a critical synchronization issue. The problem manifests as an unbalanced lock/unlock operation on the gpusvm notifier lock, which represents a fundamental flaw in the kernel's memory management and device driver coordination mechanisms. When the drm_gpusvm_scan_mm() function executes, it attempts to release a lock that was never properly acquired, creating a state where the kernel's locking subsystem becomes corrupted and potentially leads to system instability or security vulnerabilities.
The technical flaw stems from improper control flow within the function implementation where the drm_gpusvm_notifier_unlock() call is positioned under an err_free label. This positioning creates a scenario where execution can jump directly to the error handling path without first acquiring the necessary lock, subsequently attempting to release a lock that was never acquired. The kernel's locking subsystem detects this imbalance and generates a WARNING message indicating that the system is trying to release a lock when no locks are held, which violates fundamental locking principles and can result in undefined behavior.
The operational impact of this vulnerability extends beyond simple kernel panics or system crashes, as it represents a potential attack vector for privilege escalation or denial of service conditions. When the kernel's locking mechanism becomes corrupted, it can affect not only graphics processing but potentially other subsystems that rely on proper synchronization primitives. This flaw could enable malicious actors to exploit the inconsistent lock state to gain elevated privileges or cause system instability, particularly in environments where multiple processes interact with GPU memory management operations.
This vulnerability maps directly to CWE-1210 which describes improper locking scenarios in kernel code, and aligns with ATT&CK technique T1068 which covers privilege escalation through kernel vulnerabilities. The fix requires careful reorganization of the control flow to ensure that lock acquisition and release operations maintain proper balance throughout all execution paths, including error handling branches. Mitigation strategies should include immediate kernel updates from affected distributions, implementation of additional runtime checks for lock consistency, and monitoring for similar patterns in other kernel subsystems.
The root cause analysis reveals that this represents a classic example of improper resource management in kernel space where error handling code paths are not properly synchronized with the main execution flow. The vulnerability demonstrates how seemingly minor control flow issues can have catastrophic effects on system stability and security. Addressing this requires comprehensive code review processes that specifically examine all lock acquisition and release patterns, particularly in error handling sections where developers often make assumptions about program state that may not hold true under all execution conditions.
Security implications extend to potential denial of service attacks where an attacker could trigger the unbalanced unlock condition repeatedly, causing system instability or complete system crashes. The vulnerability also represents a risk for privilege escalation scenarios where inconsistent lock states might allow attackers to manipulate kernel data structures in unexpected ways. System administrators should monitor kernel logs for similar lock balance warnings and ensure that all graphics drivers are updated to versions containing the fix for this specific locking imbalance issue.
The resolution of this vulnerability requires careful attention to proper lock lifecycle management throughout the drm_gpusvm_scan_mm() function implementation. Modern kernel development practices emphasize the importance of maintaining lock balance through comprehensive testing, static analysis tools, and thorough code review processes that specifically examine error handling paths. This particular issue highlights the critical need for automated verification tools that can detect such subtle but dangerous synchronization problems in kernel code before they can be exploited in production environments.