ksmbd: vfs: fix race on m_flags in vfs_cache

Overview

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.

Affected

• Linux >= f44158485826c076335d6860d35872271a83791d < a4fd1fdf505facfae26b5654c9eff321f4cbc1a7
• Linux >= f44158485826c076335d6860d35872271a83791d < 5adad9727a815c26013b0d41cfee92ffa7d4037c
• Linux >= f44158485826c076335d6860d35872271a83791d < ccc78781041589ea383e61d5d7a1e9a31b210b93
• Linux >= f44158485826c076335d6860d35872271a83791d < ee63729760f5b61a66f345c54dc4c7514e62383d
• Linux >= f44158485826c076335d6860d35872271a83791d < 991f8a79db99b14c48d20d2052c82d65b9186cad
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.