CVE-2008-4307 in Linux
Summary
by MITRE
Race condition in the do_setlk function in fs/nfs/file.c in the Linux kernel before 2.6.26 allows local users to cause a denial of service (crash) via vectors resulting in an interrupted RPC call that leads to a stray FL_POSIX lock, related to improper handling of a race between fcntl and close in the EINTR case.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/28/2019
The vulnerability described in CVE-2008-4307 represents a critical race condition within the Linux kernel's Network File System implementation that can lead to system crashes and denial of service conditions. This flaw exists in the do_setlk function located in fs/nfs/file.c of the kernel source code and affects all Linux kernel versions prior to 2.6.26. The vulnerability stems from improper handling of concurrent operations between file locking mechanisms and file closure operations, specifically when interrupted RPC calls occur during file locking procedures. The race condition manifests when a file descriptor is closed while an fcntl system call is in progress, creating a scenario where lock structures become orphaned or improperly managed within the kernel's locking subsystem.
The technical execution of this vulnerability relies on the specific timing and interaction between multiple kernel components during NFS file operations. When an RPC call is interrupted by a signal or system event, the kernel's file locking mechanism fails to properly clean up lock structures that were in the process of being established or modified. This creates a stray FL_POSIX lock that remains in an inconsistent state, leading to kernel memory corruption when subsequent operations attempt to access or manipulate this orphaned lock structure. The race condition occurs between the fcntl system call that attempts to set or modify file locks and the close system call that terminates the file descriptor, with the interruption of the RPC call during this window causing the lock management code to lose track of the lock's proper state and associated resources.
From an operational impact perspective, this vulnerability provides local attackers with the ability to induce kernel crashes that result in system-wide denial of service conditions. The crash occurs because the kernel's memory management and lock tracking mechanisms encounter corrupted data structures when attempting to process the stray lock, leading to kernel panics or system reboots. The vulnerability is particularly concerning because it requires only local user access to exploit, making it a significant threat in multi-user environments where privilege escalation is not required. Additionally, the crash can potentially be triggered repeatedly, allowing for sustained denial of service attacks against the targeted system.
The vulnerability aligns with CWE-362, which describes a race condition in the context of concurrent access to shared resources, and demonstrates how improper synchronization mechanisms in kernel code can lead to critical system instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service attacks, and T1068, which involves exploit for privilege escalation, though in this case the escalation is implicit in the ability to cause system crashes. The fix for this vulnerability required modifications to the NFS file locking code to properly handle interrupted RPC calls and ensure that lock structures are consistently cleaned up regardless of whether the original operation completes successfully or is interrupted. This involved implementing proper synchronization mechanisms and ensuring that lock state management accounts for all possible execution paths, particularly those involving system call interruptions. The patch demonstrated the importance of robust error handling in kernel-level code and highlighted the need for comprehensive testing of concurrent operations in network file systems.