An improper locking issue leading to a race condition vulnerability was found in ksmbd, a high-performance in-kernel SMB server. Quoting ZDI security advisory [1]: "This vulnerability allows remote attackers to execute arbitrary code on affected installations of Linux Kernel. Authentication is not required to exploit this vulnerability, but only systems with ksmbd enabled are vulnerable. The specific flaw exists within the processing of SMB2_LOGOFF and SMB2_CLOSE commands. The issue results from the lack of proper locking when performing operations on an object. An attacker can leverage this vulnerability to execute code in the context of the kernel." [1] https://www.zerodayinitiative.com/advisories/ZDI-CAN-20796/
Upstream fix: https://github.com/torvalds/linux/commit/abcc506a9a71976a8b4c9bf3ee6efd13229c1e19