Linux Kernel NILFS2 Semaphore Deadlock Vulnerability

A semaphore deadlock vulnerability has been identified in the Linux kernel's NILFS2 file system. The issue arises in the nilfs_count_free_blocks() function, where a deadlock can occur if nilfs_get_block() detects metadata corruption while a superblock writeback is in progress. This situation leads to hierarchical lock acquisition conflicts, causing tasks to deadlock when trying to acquire read and write locks on semaphores in a conflicting order. The vulnerability affects several versions of the Linux kernel that include the NILFS2 file system.

Impact

Exploitation of this vulnerability leads to a deadlock condition, where tasks become stuck waiting for each other to release locks, causing a halt in processing that can degrade system performance or availability.

Remediation

The vulnerability has been addressed in the Linux kernel by modifying the nilfs_count_free_blocks() function to avoid unnecessary semaphore acquisition, thereby preventing the deadlock. Users should upgrade to the latest version of the Linux kernel where this fix is applied.