Linux Kernel NULL Pointer Dereference Vulnerability in 9p File System

A NULL pointer dereference vulnerability has been identified in the Linux kernel's 9p file system implementation. This issue occurs when a 9p tree is mounted with the 'posixacl' option, and the parent directory has a default ACL set for its subdirectories. Under these conditions, creating a subdirectory can cause a crash in the 9p client. The vulnerability arises because the 'v9fs_fid_add()' function, which is called during the directory creation process, sets the 'fid' pointer to NULL. This occurs after a specific commit, and the subsequent 'v9fs_set_create_acl()' function expects a valid, non-NULL 'fid' pointer, leading to a NULL pointer dereference error.

Impact

Exploitation of this vulnerability causes a kernel NULL pointer dereference, resulting in a crash of the 9p client.

Remediation

The vulnerability has been fixed in the official Linux Git repository. Users should upgrade to the latest version.