Linux Kernel NFS Deadlock Vulnerability in kcompactd Writeback Handling

A deadlock vulnerability has been identified in the Linux kernel's NFS (Network File System) implementation, specifically related to how the kernel's memory compaction daemon, kcompactd, manages writeback operations. When kcompactd initiates writeback, it can inadvertently cause NFS to deadlock, waiting for the writeback to complete. This issue arises because NFS, when blocked, can trigger a writeback to the NFS server daemon (NFSD) via a loopback mount, creating a circular dependency that halts processing. The vulnerability affects several versions of the Linux kernel where this NFS and kcompactd interaction is not properly managed.

Impact

Exploitation of this vulnerability leads to a severe deadlock, with the kcompactd process being blocked for an extended period, over 4,400 seconds in observed cases. This blockage can disrupt memory management operations, potentially causing performance degradation or resource exhaustion.