Linux Kernel ksmbd CVE-2025-68809

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: vfs: fix race on m_flags in vfs_cache

ksmbd maintains delete-on-close and pending-delete state in ksmbd_inode->m_flags. In vfs_cache.c this field is accessed under inconsistent locking: some paths read and modify m_flags under ci->m_lock while others do so without taking the lock at all.

Examples:

• ksmbd_query_inode_status() and __ksmbd_inode_close() use

ci->m_lock when checking or updating m_flags.

• ksmbd_inode_pending_delete(), ksmbd_set_inode_pending_delete(),

ksmbd_clear_inode_pending_delete() and ksmbd_fd_set_delete_on_close() used to read and modify m_flags without ci->m_lock.

This creates a potential data race on m_flags when multiple threads open, close and delete the same file concurrently. In the worst case delete-on-close and pending-delete bits can be lost or observed in an inconsistent state, leading to confusing delete semantics (files that stay on disk after delete-on-close, or files that disappear while still in use).

Fix it by:

• Making ksmbd_query_inode_status() look at m_flags under ci->m_lock

after dropping inode_hash_lock.

• Adding ci->m_lock protection to all helpers that read or modify

m_flags (ksmbd_inode_pending_delete(), ksmbd_set_inode_pending_delete(), ksmbd_clear_inode_pending_delete(), ksmbd_fd_set_delete_on_close()).

• Keeping the existing ci->m_lock protection in __ksmbd_inode_close(),

and moving the actual unlink/xattr removal outside the lock.

This unifies the locking around m_flags and removes the data race while preserving the existing delete-on-close behaviour.

The vulnerability affects the Linux kernel's ksmbd subsystem (vfs_cache) in versions prior to the stable trees carrying the fix commits 5adad9727a815c26013b0d41cfee92ffa7d4037c, 991f8a79db99b14c48d20d2052c82d65b9186cad, ccc78781041589ea383e61d5d7a1e9a31b210b93, and ee63729760f5b61a66f345c54dc4c7514e62383d (git.kernel.org/stable). Only systems that have the CONFIG_SMB_SERVER (ksmbd) module built and actively serving SMB shares are exposed. Ubuntu tracks the issue under USN-8177-1 (https://ubuntu.com/security/notices/USN-8177-1), and VulDB carries advisory https://vuldb.com/?id.340683. Exact vulnerable-to-fixed version boundaries depend on each distribution's kernel, since the fix was backported across multiple stable branches; consult the distro advisory for the precise fixed package version.